WNK Signaling Is Involved in Neural Development via Lhx8/Awh Expression
Citation: Sato A, Shibuya H (
WNK Signaling Is Involved in Neural Development via Lhx8/Awh Expression
Atsushi Sato 0
Hiroshi Shibuya 0
Esther Marianna Verheyen, Simon Fraser University, Canada
0 Department of Molecular Cell Biology, Medical Research Institute, Tokyo Medical and Dental University , Bunkyo-ku, Tokyo , Japan
WNK kinase family is conserved among many species and regulates SPAK/OSR1 and ion co-transporters. Some mutations in human WNK1 or WNK4 are associated with Pseudohypoaldosteronism type II, a form of hypertension. WNK is also involved in developmental and cellular processes, but the molecular mechanisms underlying its regulation in these processes remain unknown. Here, we identify a new target gene in WNK signaling, Arrowhead and Lhx8, which is a mammalian homologue of Drosophila Arrowhead. In Drosophila, WNK was shown to genetically interact with Arrowhead. In Wnk1 knockout mice, levels of Lhx8 expression were reduced. Ectopic expression of WNK1, WNK4 or Osr1 in mammalian cells induced the expression of the Lhx8. Moreover, neural specification was inhibited by the knockdown of both Wnk1 and Wnk4 or Lhx8. Drosophila WNK mutant caused defects in axon guidance during embryogenesis. These results suggest that WNK signaling is involved in the morphological and neural development via Lhx8/Arrowhead.
WNK (with no lysine (K)) is a family of serine/threonine protein
kinases that are characterized by an atypical location of the
catalytic lysine and are conserved among many species, such as
plants, nematode, fly, rat, mouse and human . There are four
mammalian WNK family members, and positional cloning has
identified two of them, WNK1 and WNK4, as genes linked to a
hereditary form of human hypertension known as
Pseudohypoaldosteronism type II (PHAII) . Several groups including our
group previously discovered that WNK1 and WNK4 could
phosphorylate and activate SPAK or OSR1 kinases, which in
turn regulates various ion co-transporters, such as NKCC1,
NKCC2 and NCC . We also found that dysregulation of
WNK1 and WNK4 in mouse kidney caused phenotypes similar to
those of PHAII . These results suggest that the dysregulation of
sodium and potassium transport by WNK1 and WNK4 contribute
to the pathogenesis of hypertension in PHAII patients.
WNK family members have also been identified in screens of
cultured cells for enhanced cell survival and proliferation .
WNK1 is required for cell division in cultured cells , and
proliferation, migration and differentiation of neural progenitor
cells . In addition, Wnk1 is ubiquitously expressed in mice, and
knockout of the gene is lethal before embryonic day 13
(Zambrowicz et al. and in this report) , with the developing
mice displaying defects in cardiac development . Furthermore,
PHAII patients exhibit other clinical problems in addition to
hypertension, such as an intellectual impairment, dental
abnormalities and impaired growth . The Drosophila genome
contains a single WNK gene (called as CG7177 in Flybase
(http://flybase.org)), which was identified in screens for genes
involved in cell cycle or neural development [10,16]. These
observations suggest that WNK1 plays unknown roles in
developmental processes, in addition to its control of ion
cotransporters in the kidney.
Here, we demonstrate that the functions of the WNK signaling
pathway are conserved between mammals and flies. Mutation of
Drosophila WNK (DWNK) caused several morphological defects.
Our functional analysis of DWNK identified a new target gene,
Arrowhead (Awh), and we found that the mammalian homologue
of Awh, Lhx8, is also a target gene of the WNK signaling pathway
in mammalian cells. Furthermore, we demonstrated that the
WNK signaling pathway modulates Drosophila development via
Awh, and modulates neural specification in mammalian cells via
Lhx8. These results reveal a novel role for WNK signaling via
Lhx8 or Awh in the regulation of morphological and neural
Materials and Methods
All animal experiments were performed under the ethical
guidelines of Tokyo Medical and Dental University, and animal
protocols were reviewed and approved by the animal welfare
committee of the Tokyo Medical and Dental University.
Fly stocks and genetics
Fly strains used in this study were; Canton-S, yw, EY10165
(UAS-DWNK; Bloomington Stock Center), fray07551, Awh63Ea-E12,
hh-Gal4, sd-Gal4, da-Gal4 and 1407-Gal4 (Bloomington Stock
Center). Flies with UAS-DWNK, UAS-DWNKD420A, UAS-hWNK1,
UAS-mOsr1, UAS-fray, UAS-frayS347D and UAS-Awh were
generated by P-mediated germline transformation (injected by BestGene
DWNKEY18, a null mutation of DWNK, is a derivative of
EY10165. DWNKEY18 has a 1712 bp deletion from the EY10165
insertion point to the middle of exon 3, which includes the
translation start site (red line in Fig. S1). However, the 59 region of
the P element of EY10165 was retained (1365 bp). We confirmed
by RT-PCR analysis that DWNKEY18 produced truncated
transcripts, by the presence of several poly-A signal sequences in the
retained P element sequences (* in Fig. S1; data not shown).
Genotypes of all fly lines we used in this study were in figure
legends. We used yellow transgene for the clonal marker; the wild
type body color represents heterozygous tissue, and yellow body
color represents mutant tissue. The mutant tissues were judged by
discrimination of the light color compared with the background of
wild type color, and the clonal borders were shown by thin black
Based on the predicted amino acid sequence of CG7177, we
confirmed the intron-exon junctions of DWNK by RT-PCR. Lhx8
cDNA for in situ probe was obtained by RT-PCR. fray (RE53265)
and Awh (RE24382) cDNA clones were obtained from Drosophila
Genomics Resource Center (Indiana, USA). Lhx8, Lhx6 and Isl1
cDNAs for the rescue experiments were obtained by RT-PCR. To
construct the kinase-dead form of DWNK and fray, and the
constitutive active of fray, we performed site-directed mutagenesis,
using the following primers: for DWNKD420A,
59GTTAAAATCGGCGCCTTGGGCCTGG -39 and
59CCAGGCCCAAGGCGCCGATTTTAAC -39; for frayK67M
59GAAGTGCGCCATTATGCGCATCAACCTGG -39 and
59CCAGGTTGATGCGCATAATGGCGCACTTC -39; for
frayS347D 59- CCAACCAGGAGCCGACGGCCGTTTGCATC
-39 and 59- GATGCAAACGGCCGTCGGCTCCTGGTTGG
In vitro kinase assay
HEK293T cells were transfected with Flag-DWNK,
FlagDWNKD420A, Flag-Fray, Flag-FrayK67M or Flag-FrayS347D expression
plasmids. The lysates were prepared from transfected cells and
immunoprecipitated with anti-Flag M2 antibody (Sigma).
Immunoprecipitates were incubated with bacterially expressed GST
fusion proteins (GST-FrayK67M or GST-NCC) in kinase buffer
containing 10 mM HEPES (pH 7.4), 1 mM DTT, 5 mM MgCl2,
and 5 mCi of [c-32P]-ATP at 30uC. Phosphorylated substrates
were subjected to SDS-PAGE, detected by an image analyzer
FLA3000 (Fujifilm) and quantified by Multi Gauge software (GE).
Antibodies used in this report were; mouse anti-Flag M2
(Sigma), rabbit anti-Flag (Sigma), mouse anti-HA (Cell signaling),
rat anti-HA (Roche), mouse anti-T7 (Merck), rabbit anti-T7
(MBL), rabbit anti-OSR1 , rabbit anti-phospho-OSR1 ,
anti-mouse HRP conjugated (GE), anti-rabbit HRP conjugated
(GE), anti-rat HRP conjugated (GE), anti-digoxigenin alkaline
phosphatase conjugated (Roche), mouse monoclonal antibody
22C10 (DSHB), rabbit anti-LacZ (Cappel; used for the selection of
Balancer chromosomes), rabbit anti-GFP (MBL), anti-rabbit IgG
AlexaFluor 488 conjugated (Invitrogen) and anti-mouse IgG Cy3
conjugated (Jackson) antibodies.
Histology and staining
All wings were mounted in GMM . Antibody staining, In
situ hybridization to fly and mouse embryos were carried out as
described previously [18,19]. For in situ hybridization,
digoxigeninlabeled RNA probes were prepared by in vitro transcription using
Awh and Lhx8 cDNA as a template. Images were obtained using
SteREO Discovery, Axioscope and Axio Observer (Carl Zeiss),
and processed using Axiovision with extended focus (Carl Zeiss)
and Photoshop (Adobe).
Wnk1 knockout mouse and microarray
The Wnk1 knockout mouse was generated by a gene-trap
insertion. The primers for genotyping of Wnk1 knockout mice
were the following: OYC4-WT 59-
AAAATACTCTGTCAGGCTTAAGTGT -39 for wild-type, LTR2
59AAATGGCGTTACTTAAGCTAGCTTGC -39 for the Wnk1
mutant and OYC4-39 59- TGAAGCCAGGCATTAAGCACTC
39 was used as a common primer.
We isolated total RNA using RNeasy kit (Qiagen). Microarray
was performed by Takara-Bio using GeneChip (Affymetrix).
Culture cell lines
Cell lines used in this study were; HEK293T, NIH3T3 and
Neuro2A . The growth medium for HEK293T cells and
NIH3T3 cells was DMEM with 10% FBS, and for Neuro2A cells,
DMEM with 20% FBS. For transfection, we used Lipofectamine
2000 (Invitrogen) or polyethylenimine (Polysciences) for plasmids
and Lipofectamine RNAiMax (Invitrogen) for siRNA. The target
sequence of siRNA against mouse WNK1 was 59-
GAUAGGGUGUCCUUAAUUA -39, against mouse WNK4 was 59-
GAAAUCGAGGACUUAUACA -39, and against mouse Lhx8 was
59AGAAUAAGCCAUUUCUUCC -39. For the hypertonic
treatments, we used serum-free DMEM with 500 mM Sorbitol for long
incubation and hypertonic buffer for short incubation. Hypertonic
buffer contained 130 mM NaCl, 2 mM KCl, 2 mM CaCl2,
2 mM MgCl2, 1 mM KH2PO4, 10 mM Glucose, 10 mM Sodium
HEPES (pH 7.4) and 520 mM Sorbitol. For the differentiation of
Neuro2A cells, we used serum-free DMEM with 10 mM retinoic
acid for 24 hours induction or DMEM with 1% FBS and 10 mM
retinoic acid for 48 hours induction.
Total RNA was isolated by TRIzol (Invitrogen). cDNA
synthesis was carried out using Moloney murine leukemia virus
reverse transcriptase (Invitrogen). The reaction mixture were
denatured at 94 degree for 5 minutes and then cycled at 98
degree/15 seconds and 72 degree/30 seconds, then followed by a
final 3 minutes extension at 72 degree (for mouse Wnk1, mouse
Wnk4, human WNK1, human WNK4, mouse Osr1, mouse Choline
acetyltransferase (ChAT), mouse Glutamic acid decarboxylase 1 (Gad1),
mouse Lhx6 and mouse Glyceraldehyde-3-phosphate dehydrogenase
(GAPDH)), or at 94 degree for 5 minutes and then cycled at 98
degree/15 seconds, 58 degree/15 seconds and 72 degree/30
seconds, then followed by a final 3 minutes extension at 72 degree
(for mouse Lhx8 and mouse Islet-1 (Isl1)). Numbers of cycles are
depending on samples (see below, number of cycles are shown
after primer sequences). GAPDH was used for normalization of
cDNA samples. The sequences of the primer pairs for PCR were
as follows: mouse Wnk1, 59-
AGAGGATGGCTCAGGTAGTCCACAC -39 and 59- AACACACAGCTGCCCAGGAGCAGAG
-39 (29 cycles), mouse Wnk4, 59-
AAGCTCTGGCTGCGCATGGAGGATG -39 and 59-
GGATCGAGGTCTCCGTCGAAGAGTC -39 (32 cycles), human WNK1, 59-
AAGTTAGAGCTGCGACGACTACGAG -39 and 59-
GGTGCAGAGAACTTCCTTGCCATTC -39 (25 cycles), human WNK4,
59CCAAGTGACTTCATCCAAGGAACCG -39 and 59-
TCAGAGAGTTCCTTCGCATGATGCC -39 (25 cycles), mouse Osr1,
59- TGGCCGTCTCCATAAGACAGAGGAC -39 and
59TATCCGAGCCTTCAACACCAGATGC -39 (24 cycles), mouse
Lhx8, 59- GACCCAGCTGCCAATAAGTCATACC -39 and
59GACACACACTCGAGCCAACTATCTC -39 (35 cycles), mouse
ChAT, 59- CAGTGCATGCAACACCTGGTACCTG -39 and
59GAACAGATCACCCTCACTGAGACGG -39 (45 cycles), mouse
Gad1, 59- CATCTTCCACTCCTTCGCCTGCAAC -39 and
59CAGTCAACCAGGATCTGCTCCAGAG -39 (40 cycles), mouse
Lhx6, 59- CACTCTGCGCCTCTCTTCGCACTGC -39 and
59ATGTGCGACACACGGAGCACTCGAG -39 (36 cycles),
mouse Isl1, 59- ACATCGAGTGTTTCCGCTGTGTAGC -39
and 59- CTACTGGGTTAGCCTGTAAACCACC -39 (28 cycles)
and mouse GAPDH, 59-
GCCATCACTGCCACCCAGAAGACTG -39, and 59- CATGAGGTCCACCACCCTGTTGCTG
-39 (21 cycles). The whole gel images of all PCR results are shown
in Fig. S9.
Quantification and statistical analysis
All results from Western blotting were quantified using Multi
Gauge software (GE). Quantitative PCR was performed with an
Applied Biosystems 7300 Real-Time PCR Cycler (ABI) using
THUNDERBIRD SYBR qPCR Mix (TOYOBO). The sequences
of the primer pairs for Lhx8, ChAT, Gad1 and GAPDH were
described previously . GAPDH was used for normalization
of cDNA samples. Data are computed using Microsoft Exel
(Microsoft). Values and error bar represent the mean and SD and
are representative of at least 3 independent experiments.
WNK- SPAK/OSR1 pathway is conserved between
mammals and flies
The Drosophila genome contains only one WNK homologue
CG7177, which we hereafter refer to as Drosophila WNK (DWNK;
Fig. S1). In contrast, there are four WNK family genes in
mammals. Among the mammalian WNK proteins, DWNK was
most homologous to WNK1 (Fig. S1). Recent studies have shown
that mammalian WNK14 interact with and phosphorylate the
STE20 kinases, SPAK and OSR1 . As Drosophila Fray is a
homologue of SPAK and OSR1 , we investigated whether the
biochemical interaction between DWNK and Fray is conserved in
Drosophila. We transiently expressed HA-DWNK together with
T7-Fray in human embryonic kidney (HEK) 293T cells. When cell
extracts were subjected to immunoprecipitation with the HA
antibody, followed by immunoblotting, we found that DWNK
interacted with Fray (Fig. 1A, lane 3). We next investigated
phosphorylation of Fray by DWNK. We produced a glutathione
S-transferase (GST)-tagged kinase-negative form of FrayK67M in
bacteria and tested its ability to be phosphorylated in vitro. We
observed that DWNK phosphorylated Fray in a kinase-dependent
manner (Fig. 1B, lanes 4, 8). We attempted to generate a
constitutively activate form of Fray by mutating Ser to Asp at
amino acid 347, which corresponds to the site of WNK
phosphorylation in mouse Osr1 [5,6]. Fray kinase activity was
assayed using an amino-terminal fragment of NCC, GST-NCC, as
a substrate . This mutant, FrayS347D, exhibited increased
phosphorylation of GST-NCC, relative to wild-type Fray (Fig. 1C
lane 4,12), indicating that the mutation of Ser-347 to Asp causes
constitutive activation of Fray.
To examine the functional conservation of human and
Drosophila WNK, we used the UAS-Gal4 system to express human
WNK in Drosophila. We made an expression construct of human
WNK1 (hWNK1) and generated UAS-transgenic flies
(UAShWNK1). As a UAS-DWNK line, we used the EY10165 line, in
which the pEY construct has been inserted into the 1st exon of the
DWNK gene (Fig. S1B). Although any wing phenotypes were not
obtained from either the heterozygous UAS-DWNK or hedgehog
(hh)-Gal4 driver line (Fig. 2BC compared with Fig. 2A, and see
also Fig. S2), we observed that the phenotypes of DWNK
overexpression using hh-Gal4 driver were similar to those of
hWNK1 overexpression (Fig. 2DE compared with Fig. 2A; extra
veins around vein 5 and delta phenotypes at vein 4 in the wing; see
also Fig. S2). We also generated UAS-transgenic flies of mouse
Osr1 (mOsr1; UAS-mOSR1) and its fly homologue, fray (UAS-fray)
. Wing phenotypes of the flies overexpressing mOsr1 were
similar to those overexpressing fray (Fig. 2FG and Fig. S2). To
analyze the genetic interaction between DWNK and Fray, we
examined the phenotypes of DWNK overexpression in a
heterozygous fray mutant (fray07551) background. Heterozygous fray07551
has a normal-looking wing. The penetrance of wing phenotypes
induced by DWNK overexpression were partially rescued in a
heterozygous fray07551 mutant background (Fig. 2H and Fig. S2).
Moreover, the wing phenotypes induced by frayS347D, the
constitutively active form of Fray driven by hh-Gal4, were more
frequent, but similar phenotypes to those seen in flies
overexpressing mOsr1or fray (Fig. 2I and Fig. S2). We also generated an
inactive mutant of DWNK, DWNKEY18, by imprecise P element
excision (Fig. S1; see also Materials and Methods for detail
characterization of DWNK mutant). Heterozygous DWNKEY18
mutant did not cause any phenotype in wing. The penetrance of
the phenotypes of frayS347D overexpression could not be rescued in
a heterozygous DWNKEY18 background (Fig. 2J and Fig. S2).
Taken together, these results suggest that Fray functions
downstream of DWNK, and that the WNK-SPAK/OSR1/Fray
pathway is conserved among many species.
DWNK-Fray pathway functions in abdominal
To investigate the developmental function of DWNK, we
generated UAS system constructs for the expression of the
kinasedead form of DWNK (UAS-DWNKD420A). As the expression of
DWNKD420A by hh-Gal4 caused lethal, we switched to sd-Gal4
driver. The expression of DWNKD420A by sd-Gal4 driver induced
the loss of wing margin (Fig. S3). In addition, the expression of
DWNKD420A by sd-Gal4 driver caused the complete disruption of
abdominal differentiation in the pharate adults (compared Fig. 3B
with Fig. 3A). To confirm that these phenotypes were caused by
the loss of DWNK, we examined the adult phenotypes of
DWNKEY18. We employed a mosaic analysis since homozygous
DWNKEY18 flies die between late embryonic stage and early 2nd
instar larva. Various phenotypes, such as extra veins in the wing
and loss of macrocheate or microcheate bristles in the notum, were
observed in the large DWNKEY18 clones generated by Minute
methods (Fig. S3). Moreover, the defects in abdominal
development were observed in the mosaic clones (Fig. 3C). We also
observed that the abdominal phenotypes were almost rescued by
the overexpression of DWNK (Fig. S4), suggesting that the
abdominal phenotypes were the results of DWNK deficiency.
These observations indicate that phenotypes induced by the
kinase-dead form of DWNK, DWNKD420A, were indeed caused
by loss of DWNK function, suggesting that DWNKD420A worked
as a dominant negative.
Next, we examined whether Fray also worked at the
downstream of WNK in abdominal development. While the
expression of the constitutively active form of fray, frayS347D, did not
cause any phenotype in abdomen (Fig. 3D), the abdominal defects
caused by DWNKD420A could be rescued by the expression of
frayS347D (Fig. 3E). We also confirmed that this rescue was not due
to the titration of Gal4 expression by adding another UAS
construct (Fig. S5). Thus, these results suggest that DWNK-Fray
pathway plays important roles in Drosophila abdominal
Genetic interaction of DWNK with Awh
Both the DWNK minute clones and flies expressing the
dominant-negative form of DWNK exhibited defects in abdominal
development (Fig. 3BC). Similar abdominal phenotypes have
been previously described for the Arrowhead (Awh) mutant (Fig. 3F)
, a transcription factor of the Lim homeobox type. We
therefore investigated whether DWNK genetically interacts with
Awh. We generated UAS-Awh lines and induced Awh expression by
sd-Gal4 driver, together with or without DWNKD420A expression.
Overexpression of Awh did not affect the abdominal development
(Fig. 3G). However, the defect in abdominal development caused
by expression of DWNKD420A was rescued in flies co-expressing
Awh (Fig. 3H and 3B). We also tested whether expression of Awh
rescued the abdominal phenotype of DWNK minute clones. Using
a combination of the FLP/FRT mosaic system and Gal80
suppression, we could express Awh locally in DWNK minute
clones. As shown in Fig. 3I, overexpression of Awh partially
rescued the abdominal phenotype of DWNK minute clones. These
results indicate that DWNK genetically interacts with Awh.
WNK regulates the expression of the Awh/Lhx8 gene
The mammalian homologue of Awh is Lhx8 (also called L3 or
Lhx7) . To analyze how Lhx8 functions in the WNK
signaling pathway, we first examined whether WNK1 binds to
Lhx8 or regulates expression of the Lhx8 gene. We were unable to
detect an interaction between ectopically expressed WNK1 and
Lhx8 in cultured cells (data not shown). We performed microarray
analyses using embryos of wild-type or Wnk1 knockout mice at
embryonic day 9. These microarray data revealed that Lhx8
expression was reduced in Wnk1 knockout mice (Fig. 4A). We also
examined Lhx8 expression in developing mice embryos by in situ
hybridization. As previously reported , Lhx8 was expressed in
the craniofacial region of wild-type embryos at embryonic day
10.5 (Fig. 4B). In contrast, Lhx8 expression was very weak in the
similar region of Wnk1 knockout mice embryos (Fig. 4C).
Moreover, we examined whether DWNK controls Awh expression
in Drosophila embryos. Awh was expressed in a striped pattern at
stages 11 and 13 (Fig. 4DE), and in the histoblast nest (which is
the primordia of abdominal tissue) at stage 16 (arrows in Fig. 4F).
We could not detect expression of Awh in the histoblast nests of
embryos homozygous for DWNKEY18 at stage 16 (Fig. 4I).
However, expression of Awh in embryos homozygous for
DWNKEY18 at stages 11 and 13 was not changed (data not shown).
We expected that the zygotic mutant embryos of DWNKEY18
would be rescued by maternal transcripts of DWNK, since DWNK
is maternally expressed according to the High Throughput
Expression Data in Flybase (http://flybase.org). Instead, we found
that expression of Awh at stages 11 and 13 was reduced in the
embryos overexpressing DWNKD420A driven by da-Gal4 (Fig. 4G
H). Together, these results suggest that the expression of the Awh/
Lhx8 gene is regulated by WNK.
The WNK-SPAK/OSR1 pathway induces expression of the
We further attempted to examine Lhx8 gene expression in the
WNK-SPAK/OSR1 pathway. A previous study has reported that
WNKs are activated by hypertonic stimulation . We first
performed Western blotting analysis using anti-phospho OSR1
antibody, which recognizes Ser325 of mOsr1 phosphorylated by
WNK kinases5, whether WNKs are activated by hypertonic
stimulation in NIH3T3 cells. We found that WNKs were
immediately activated by hypertonic stimulation in NIH3T3 cells
(Fig. 5A lanes 15). On the other hand, knockdown of either Wnk1
or Wnk4 using siRNA significantly reduced the phophorylation
level of mOsr1 (Fig. 5A lanes 610 or 1115). Moreover, the
knockdown of both Wnk1 and Wnk4 synergistically caused the loss
of the phosphorylation of mOsr1 (Fig. 5A lanes 1620). Next, we
performed RT-PCR analysis to ask whether the expression of Lhx8
gene is activated under hypertonic conditions. We found that Lhx8
expression was induced in NIH3T3 cells by hypertonic stimulation
for 8 hours (Fig. 5B lanes 14). Knockdown of either Wnk1 or
Wnk4 using siRNA resulted in significantly reduced induction of
Lhx8 (Fig. 5B lanes 58 or 912). In addition, Lhx8 activation was
completely suppressed by knockdown of both Wnk1 and Wnk4
(Fig. 5B lanes 1316). Conversely, Lhx8 expression was induced by
the expression of hWNK1 or hWNK4 (Fig. 5C lanes 2 and 4).
Although expression of a kinase-dead form of either hWNK1 or
hWNK4 (hWNK1D368A or hWNK4K186M) also weakly activated
Lhx8 expression (Fig. 5C lanes 3 and 5), co-expression of both
hWNK1D368A and hWNK4K186M did not activate Lhx8 expression
(Fig. 5C lane 6). Phosphorylation of Osr1 was also confirmed to
correlate with the expression of Lhx8 (Fig. 5C bottom two rows).
Moreover, expression of wild-type mOsr1 also induced Lhx8
expression (Fig. 5D lane 2). The expression of mOsr1K46M, the
kinase-dead form of mOsr1, did not induce Lhx8 expression
(Fig. 5D lane 3). Furthermore, expression of mOsr1S325D, the
constitutively active form of mOsr1, strongly induced Lhx8
expression (Fig. 5D lane 4). On the other hand, induction of
Lhx8 induced by expression of WNK1 was completely suppressed
when Osr1 was knocked down using siRNA (Fig. 5E lane 4). In
addition, the prior treatment of cycloheximide (CHX), an inhibitor
of protein biosynthesis, did not inhibit Lhx8 expression by
hypertonic stimulation (Fig. 5F), indicating that Lhx8 is a direct
target gene in WNK activation through hypertonic stimulation.
These results suggest that the WNK-OSR1 pathway regulates
Lhx8 expression, and that Lhx8 is a downstream target gene in the
WNK signaling pathway.
The WNK signaling pathway is involved in neural
It is known that Lhx8 is involved in the determination of
cholinergic neural fate in the forebrain [30,31], and the
specification of neural fate in Neuro2A cells that are able to
differentiate into cholinergic or GABAergic neurons .
Moreover, WNK1 is known to play an important role in the
proliferation, migration and differentiation of neural progenitor
cells . Thus, we speculated that the WNK signaling pathway
might be involved in neural differentiation via expression of the
Lhx8 gene. Since retinoic acid (RA) is known to induce
differentiation of Neuro2A cells, we investigated whether RA is
able to activate WNK signaling. We performed Western blotting
analysis using anti-phospho OSR1 antibody. We found that
phosphorylation of mOsr1 increased at around 2 to 4 hours after
RA stimulation (Fig. 6A), indicating that WNK kinases were
activated by RA in Neuro2A cells. We also found that expression
of the Lhx8 gene was induced by RA in Neuro2A cells (Fig. 6B).
After treatment with RA for 24 hours, Neuro2A cells were clearly
differentiated and had generated several elongated neurites
(Fig. 6C; see also Fig. S6). RA-induced neurite elongation was
not suppressed by siRNA knockdown of either Wnk1 or Wnk4
alone in Neuro2A cells (Fig. 6DE), but was inhibited by the
combined knockdown of both Wnk1 and Wnk4 (compare Fig. 6F
with Fig. 6C). Moreover, knockdown of Lhx8 also inhibited neurite
elongation (Fig. S6). These results suggest that the WNK signaling
pathway is involved in the elongation of neurites.
To confirm the neural fate of the differentiated Neuro2A cells,
we examined the expression of marker genes by RT-PCR analysis.
Choline acetyltransferase (ChAT) or Glutamic acid decarboxylase 1 (Gad1)
was used as a marker for cholinergic or GABAergic neurons,
respectively. After treatment of RA for 24 hours, Neuro2A cells
differentiated into neurons and expressed the marker genes, ChAT
and Gad1 (Fig. 6G lane 3). As previously reported , we
confirmed that knockdown of Lhx8 expression caused a decrease in
ChAT expression and increase in Gad1 expression (Fig. 6G lane 4).
Knockdown of Wnk1 or Wnk4 caused a decrease in ChAT and
increase in Gad1 expression, compared to cells treated with control
siRNA (Fig. 6H lanes 9,11,13 and 6I lanes 9,11,13). In addition,
knockdown of both Wnk1 and Wnk4 completely reduced ChAT
expression (Fig. 6H lane 15 and 6I lane 15). These results suggest
that the WNK kinases are involved in the specification of neural
set to 100. (HI) Neuro2A cells were transfected with various combinations of siRNAs and expression plasmids and gene expressions by RT-PCR or
quantitative RT-PCR analysis were examined. Cells were treated with control siRNA (Control) in lanes 1,2,9,10, with siWnk1in lanes 3,4,11,12, with
siWnk4 in lanes 5,6,13,14, and with both siWnk1 and siWnk4 in lanes 7,8,15,16. Cells were also transfected with control expression vector pRK5 in lanes
1,3,5,7,9,11,13,15 and with mOsr1S325D (H) or Lhx8 (I) overexpression vector in lanes 2,4,6,8,10,12,14,16. Cells were left undifferentiated in lanes 18
and differentiated cells by RA for 24 hours (H) or 48 hours (I) in lanes 916. The value obtained from each samples was normalized to the level of
GAPDH. The value of Lhx8, ChAT or Gad1 from differentiated cells under the treatment of control siRNA (lane 9 in both H and I) was set to 100.
These results indicate that Lhx8 expression correlates with the
activities of the WNK kinases. Thus, we first examined whether
expression of the constitutively active form of mOsr1 (mOsr1S325D)
rescues the neural specification phenotype induced by knockdown
of both Wnk1 and Wnk4. While the expression of mOsr1S325D did
not affect and could rescue the elongation of neurite (Fig. S6),
mOsr1S325D overexpression significantly induced Lhx8 expression
even in undifferentiated Neuro2A cells (Fig. 6H lane 2,4,6,8) and
also affected an enhancement in ChAT expression and a reduction
in Gad1 expression with RA treatment in Neuro2A cells (Fig. 6H
lane 910). Under the condition of the knockdown of both Wnk1
and Wnk4, mOsr1S325D overexpression could rescue Lhx8
expression, the decreasing of ChAT and increasing of Gad1 (Fig. 6H lane
1516). On the other hand, Lhx8 overexpression did not affect the
elongation of neurites (Fig. S6), but could not rescue the elongation
of neurites caused by the knockdown of both Wnk1 and Wnk4 (Fig.
S6). Lhx8 overexpression also caused an enhancement in ChAT
expression and a reduction in Gad1 expression (Fig. 6I lane 910).
However, Lhx8 overexpression could not rescue the decrease in
ChAT or increase in Gad1 expression caused by knockdown of both
Wnk1 and Wnk4 (Fig. 6I lane 1516). These results suggest that
WNK-OSR pathway is involved in the neural development, and
that Lhx8 is necessary but not sufficient for the specification of the
The WNK signaling pathway is involved in neural
development in Drosophila
Since Fray was required for axonal ensheathment  and Awh
was expressed in neuroblasts in stage 9 embryos in Drosophila ,
we wondered whether the WNK signaling pathway was also
involved in neural development during Drosophila development. To
analyze this possibility, we examined the formation of the
peripheral nervous system in fly embryos by staining with
22C10 monoclonal antibodies, which can visualize neuronal
morphology and axonal projections [33,34] (Fig. 7A). We could
find only a few DWNKEY18 embryos exhibiting minor defects of
axon guidance (arrows in Fig. 7B). These are expected that the
zygotic mutant embryos of DWNKEY18 would be rescued by
maternal transcripts of DWNK, as explained above. Therefore to
better confirm this result, we examined the effects of a dominant
negative form of DWNK. We found that the expression of a
dominant negative form of DWNK (DWNKD420A) driven by the
1407-Gal4 driver, which expressed in neuroblast and nervous
system , also caused severe defects in the peripheral nervous
system (Fig. 7C). We next tested whether Fray or Awh could rescue
the phenotypes. While overexpression of the constitutively active
form of fray (frayS347D) did not cause any phenotypes (Fig. 7D), the
constitutively active form of fray could rescue the effects of the
dominant negative form of DWNK (Fig. 7E). On the other hand,
overexpression of Awh did not cause any defects of axon guidance
(Fig. 7F), and could not rescue the phenotypes by overexpression
of DWNKD420A (Fig. 7G). We also confirmed that the rescue by the
co-expression of frayS347D was not due to the titration of Gal4
expression (Fig. S5). These results suggest that DWNK-Fray
pathway plays an important role in neural development in
Drosophila, but that Awh is not sufficient for determinant in neural
The WNK-SPAK/OSR1 pathway is known to regulate various
ion co-transporters and is widely conserved among many species
[1,2]. Wnk1 knockout mice die before embryonic day 13
(Zambrowics et al. and in this report) , and display defects
in cardiac development . WNK1 is also required for cell
division in cultured cells , and proliferation, migration and
differentiation of neural progenitor cells . Furthermore, PHAII
patients display a number of other clinical features, such as an
intellectual impairment, dental abnormalities and impaired growth
in addition to hypertension . Accordingly, the new role of the
WNK signaling pathway described here may provide further
insight into the development and pathogenesis of PHAII. In this
study, we have identified Lhx8/Awh as a new downstream
molecule in the WNK-SPAK/OSR1 pathway and discovered a
novel function for the WNK-Lhx8 pathway in neural
There are four mammalian WNK family members, and WNK1
and WNK4 genes are linked to a hereditary form of human
hypertension known as Pseudohypoaldosteronism type II (PHAII)
. In Drosophila, only one WNK gene, DWNK, has been
identified. We found that both the wild-type and kinase-dead
forms of WNK1 or WNK4 caused the up-regulation of Lhx8 gene
expression in NIH3T3 cells (Fig. 5D lanes 25). Similarly, our
previous study showed that SPAK, a substrate of WNK1, was
weakly phosphorylated by the kinase-dead form of WNK1
following a long incubation . These results are inconsistent
with the idea that the kinase-dead form of DWNK functions as a
dominant-negative mutant in Drosophila. Studies of WNK1 and
WNK4 suggest that these molecules phosphorylate each other and
coordinated to regulate NaCl cotransport . Therefore, these
results raised the possibility that the kinase-dead forms of WNK1
and WNK4 coordinate with their respective endogenous WNK1
and WNK4 counterparts in mammalian cells. In fact, we found
that co-expression of both kinase-dead forms of WNK1 and
WNK4 did not cause either induction of Lhx8 gene expression or
phosphorylation of mOsr1 (Fig. 5D lane 6). These results suggest
that the kinase activity of WNKs is required for induction of Lhx8
gene expression and the activation of SPAK/OSR1, and that the
kinase-dead form of WNK acts as an actual dominant-negative
form in the signaling pathway. Furthermore, the expression of
Lhx8 by either hypertonic or RA stimulation was required for the
expression of both WNK1 and WNK4 (Fig. 5B lanes 1316, 6I
lane 15 and 6J lane 15). Taken together, these results suggest that
WNK1 and WNK4 function coordinately and redundantly in
A previous report demonstrated that WNK1 might control the
formation of microtubules in developing neurons . On the
other hand, other studies suggested that Lhx8 plays an important
role in the development of basal forebrain cholinergic neurons
[30,31,37], that Fray is required for axonal ensheathment ,
and that Awh is expressed in neuroblasts in stage 9 embryos in
Drosophila . In this study, we showed that the WNK-OSR1
pathway regulates Lhx8 gene expression, that knockdown of both
Wnk1 and Wnk4 in Neuro2A cells caused a shortening of neurites,
as well as reduced Lhx8 expression (Fig. 6GJ and Fig. S6), and
that the expression of the constitutively active form of mOsr1,
mOsr1S325D, could rescue the phenotype caused by the
knockdown of both Wnk1 and Wnk4 (Fig. 6I and Fig. S6). In addition,
mutation of DWNK or expression of a dominant-negative form of
DWNK in fly embryos caused defects in axon guidance in the
peripheral nervous system (Fig. 7B,C), and the constitutively active
form of fray, frayS347D, expression could rescue the phenotypes by
the expression of the dominant negative form of DWNK (Fig. 7E).
Furthermore, ubiquitous expression of Awh by da-Gal4 showed
severe defects of axon guidance as similar to DWNKD420A
expression by da-Gal4 (Fig. S7), although neural specific expression
of Awh did not showed any phenotype (Fig. 7F). Taken together,
these findings clearly indicate that the WNK-OSR1/Fray-Lhx8/
Awh pathway is involved in neural development. However, the
phenotypes caused by knockdown of both Wnk1 and Wnk4, such as
the shortening of neurites and the reduction in ChAT expression,
were not rescued by the expression of Lhx8 in Neuro2A cells
(Fig. 6J and Fig. S6). In addition, the expression of Awh could not
rescue the defects in the peripheral nervous system by the
expression of the dominant-negative form of DWNK (Fig. 7G).
Previous reports showed that Lhx8 might work with other factors,
such as Lhx6 or Isl1 [27,37,38]. However, we also found that the
expression of Lhx6 and/or Isl1 with Lhx8 could not rescue the
defects by knockdown of both Wnk1 and Wnk4 in Neuro2A cells
(Fig. S8). These results suggest that other molecule(s) are involved
in neural differentiation induced by WNK signaling. Our studies
may provide the first evidence identifying a target gene that acts
downstream in the WNK-SPAK/OSR1 pathway, and
demonstrate the significance of the WNK-OSR1-Lhx8 pathway in neural
development. However, the details of how other unknown
molecules controlled by WNK signaling specifically contribute to
neural developmental remain to be determined and will require
Genetic mutations of WNK1 or WNK4 in PHAII patients result in
abnormal expression of the WNK1 gene or WNK4 kinase activity,
respectively . Abnormal activation of the WNK signaling
pathway caused by these mutations result in the misregulation of
NCCs in the kidney, which in turn causes hypertension [59,39].
However, PHAII patients display other clinical features, such as an
intellectual impairment, dental abnormalities and impaired growth
. Although these features are also thought to be caused by
WNK1 or WNK4 mutations, the details of how these pathologies
occur are unknown except for hypertension. In this study, we
identified Lhx8 as a downstream target of the WNK signaling
pathway (Fig. 5). We also found evidence that the WNK-Lhx8
pathway is involved in neural development (Fig. 6). Previous studies
have shown that knockdown of Lhx8 using antisense
oligodeoxynucleotides caused the loss of tooth germ , and Lhx8 and Lhx6
are key regulators of mammalian dentition . Furthermore, Lhx8
knockout mice show a reduction in the number of cholinergic
neurons in the ventral forebrain [30,31,37] and exhibit a severe
deficit in spatial learning and memory . These observations
indicate that Lhx8 has essential functions in the formation of the
tooth development, the specification of the cholinergic neurons and
the processing of the spatial information in mice. Therefore, the
similarities between the clinical features of PHAII and the
phenotypes of Lhx8 knockdown or knockout mice strongly suggest
that the WNK-Lhx8 pathway is involved in the pathogenesis of
PHAII, aside from hypertension. Further investigation will be
needed to prove this hypothesis.
Figure S1 WNK family proteins in human and fly, and
the genetic map of DWNK locus. (A) The homology among
WNKs in humans and Drosophila. Red boxes indicate kinase
domains. The percentages under the red boxes are the %
homology to human WNK1. Green boxes indicate auto-inhibitory
domains. Sky blue boxes are coiled-coil domains. Yellow boxes are
acidic regions. (B) Genomic locus of the Drosophila WNK gene. pEY
construct inserted into 1st exon in EY10165 line, and the
translational start site was deleted in DWNKEY18 mutant. White
boxes are untranslated regions. Black boxes are coding regions.
Red line indicates the region deficient in the DWNKEY18 mutant.
Figure S3 The phenotypes of DWNKD420A
overexpression or DWNKEY18 minute mosaic clones in wing or
notum. (A) Wing from DWNKD420A overexpressing flies driven by
sd-Gal4 showed the loss of wing margins. Arrowhead shows the loss
of wing margin. Note that DWNKD420A overexpressing flies are
raised at 20uC. Dorsal is up. Distal is right. (BC) Wings with
minute mosaic clones of DWNKEY18 mutant showed the loss of
wing margin or the extra vein. Arrowhead shows the loss of wing
margin (B) and arrow shows the extra vein (C). Dorsal is up. Distal
is right. Note that we didnt observe wing, which had both the loss
of wing margin and the extra vein. The numbers of wings showing
phenotypes and of total observed wings were indicated. (D) Dorsal
view of adult notum with minute mosaic clones of DWNKEY18
mutant showed the loss of both macro- and microchaetes. Thin
black lines indicate the clone border. White arrows indicate the
loss of microchaetes. White arrowheads indicate the loss of
dorsocentral bristles. Anterior is up. The number of notums showing
phenotypes and of total observed notums were indicated, but we
could not estimate a penetrance, since clones were randomly
induced by heat shock. The detail genotypes in this figure were
followings: (A) w sd-Gal4/+; UAS-DWNKD420A/+: (BD) y w hsflp;
DWNKEY18 FRT2A/hsGFP hsCD2(y+) M(3)i55 ri FRT2A.
Figure S4 The rescue of the abdominal phenotypes by
DWNK mutant clones. (A) Abdomen from adult with
DWNKEY18 minute clones and DWNK overexpression. DWNK
was expressed only in DWNKEY18 minute clones using the Gal80
suppression technique. Thin black lines indicate the clone border
(also DWNK expression area). Black arrows or black arrowheads
show rescued abdominal cuticles or bristles, respectively. Dorsal
views. Anterior is up. The detail genotype in this figure was
followings: y w UAS-DWNK/y w hsflp; arm-Gal4/+; DWNKEY18
FRT2A/hsGFP hsCD2(y+) M(3)i55 Tub.Gal80 FRT2A.
Figure S5 The titration of Gal4 lines. (AA9) Abdomen
from pharate adult co-overexpressing DWNKD420A and GFP
driven by sd-Gal4. Dorsal views. Anterior is up. (BB0) Lateral
views of Drosophila embryos co-overexpressing DWNKD420A and
GFP driven by 1407-Gal4 at stage 16 stained by 22C10
monoclonal antibodies (pink) and anti-GFP antibodies (green).
Anterior is left. Dorsal is up. The detail genotypes in this figure
were followings: (A) w sd-Gal4/+; UAS-DWNKD420A/+;
UASGFP/+: (B) y w hsflp/w; UAS-DWNKD420A/1407-Gal4; UAS-GFP/
Figure S6 The phenotypes of the knockdown of Lhx8 or
the knockdown of Wnk1 and/or Wnk4 with or without
concomitant mOsr1S325D or Lhx8 overexpression in
Neuro2A cells. (AB) The knockdown of Lhx8 caused the
shortening of neurites. Differentiation of siRNA-treated Neuro2A
cells induced by retinoic acid (RA) for 24 hrs; (A) Control siRNA
or (B) siLhx8. (CN) mOsr1S325D overexpression could, but Lhx8
overexpression could not rescue the shortening phenotype of
neurites by the knockdown of both Wnk1 and Wnk4.
Differentiation of siRNA-treated Neuro2A cells induced by RA for 24 hours
(mOsr1S325D) or 48 hours (Lhx8) with or without concomitant
mOsr1S325D or Lhx8 overexpression; (C,G,K) Control siRNA,
(D,H,L) siRNA against mWnk1 (siWnk1), (E,I,M) siRNA against
mWnk4 (siWnk4), (F,J,N) both siWnk1 and siWnk4 (siWnk1+siWnk4),
Figure S7 The neural defects by da-Gal4. (AB) Lateral
views of Drosophila embryos at stage 16 stained by 22C10
monoclonal antibodies. Dorsal views. Anterior is up. (A) Embryos
overexpressing DWNKD420A driven by da-Gal4. (B) Embryos
overexpressing Awh driven by da-Gal4. The numbers of embryos
showing phenotypes and of total observed embryos were indicated.
Anterior is left. Dorsal is up. The detail genotypes in this figure
were followings: (A) y w hsflp; UAS-DWNKD420A/+; da-Gal4/+: (B) y
w hsflp; UAS-Awh/+; da-Gal4/+.
Figure S8 Expression of Lhx6 and/or Isl1 with Lhx8
could not rescue the phenotypes by the knockdown of
both mWnk1 and mWnk4 in Neuro2A cells. (AL) Lhx6
and/or Isl1 expression with Lhx8 expression could not rescue the
shortening phenotype of neurites by the knockdown of both Wnk1
and Wnk4. Differentiation of siRNA-treated Neuro2A cells
induced by RA for 24 hours with or without concomitant Lhx6,
Isl1 and/or Lhx8 expression; (AF) Control siRNA, (GL) both
siWnk1 and siWnk4 (siWnks), (A,G) with control vector (pRK5),
(B,H) with Lhx6 expression vector, (C,I) with Isl1 expression
vector, (D,J) with Lhx8 and Lhx6 expression vectors, (E,K) with
Lhx8 and Isl1 expression vectors or (F,L) with Lhx8, Lhx6 and Isl1
expression vectors. (M) Gene expressions by RT-PCR or
quantitative RT-PCR analysis were examined in Neuro2A. Cells
treated with siRNA against both mWnk1 and mWnk4; Cells were
treated with control siRNA (Control) in lanes 16 and 1318, with
both siWnk1 and siWnk4 (siWnks) in lanes 712 and 1924. Cells
were also transfected with control expression vector pRK5 in lanes
1,7,13,19, with Lhx6 expression vector in lanes 2,8,14,20, with Isl1
expression vector in lanes 3,9,15,21, with Lhx8 and Lhx6
expression vectors in lanes 4,10,16,22, with Lhx8 and Isl1
expression vectors in lanes 5,11,17,23, or with Lhx8, Lhx6 and
Isl1 expression vectors in lanes 6,12,18,24. (lanes 112)
undifferentiated cells, (lanes 1324) cells differentiated by RA for 24 hours.
The value obtained from each samples was normalized to the level
of GAPDH. The value of ChAT and Gad1 from differentiated cells
under the treatment of control siRNA (lane 13) was set to 100.
The gel images of all PCR results.
We thank Andrew Tomlinson, Takahiro Chihara and the Bloomington
stock center for fly stocks, Drosophila Genomics Resource Center for
cDNA clones, Tetsuo Moriguchi for materials and helpful discussion,
Tomoko Yamanaka and Yoko Mitsutomo for technical assistance, and
Marc Lamphier for critical reading of the manuscript. We also thank
BestGene Inc. for the germ-line transformation of flies.
Conceived and designed the experiments: HS AS. Performed the
experiments: AS. Analyzed the data: AS HS. Contributed reagents/
materials/analysis tools: AS HS. Wrote the paper: AS HS.
1. Moniz S , Jordan P ( 2010 ) Emerging roles for WNK kinases in cancer . Cell Mol Life Sci 67 : 1265 - 1276 .
2. Verssimo F , Jordan P ( 2001 ) WNK kinases, a novel protein kinase subfamily in multi-cellular organisms . Oncogene 20 : 5562 - 5569 .
3. Xu B , English JM , Wilsbacher JL , Stippec S , Goldsmith EJ , et al. ( 2000 ) WNK1, a novel mammalian serine/threonine protein kinase lacking the catalytic lysine in subdomain II . J Biol Chem 275 : 16795 - 16801 .
4. Wilson FH , Disse-Nicode`me S , Choate KA , Ishikawa K , Nelson-Williams C , et al. ( 2001 ) Human hypertension caused by mutations in WNK kinases . Science 293 : 1107 - 1112 .
5. Moriguchi T , Urushiyama S , Hisamoto N , Iemura S , Uchida S , et al. ( 2005 ) WNK1 regulates phosphorylation of cation-chloride-coupled cotransporters via the STE20-related kinases, SPAK and OSR1 . J Biol Chem 280 : 42685 - 42693 .
6. Vitari AC , Deak M , Morrice NA , Alessi DR ( 2005 ) The WNK1 and WNK4 protein kinases that are mutated in Gordon's hypertension syndrome phosphorylate and activate SPAK and OSR1 protein kinases . Biochem J 391 : 17 - 24 .
7. Gagnon KB , England R , Delpire E ( 2006 ) Volume sensitivity of cation-Clcotransporters is modulated by the interaction of two kinases: Ste20-related proline-alanine-rich kinase and WNK4 . Am J Physiol Cell Physiol 290 : C134 - 142 .
8. Piechotta K , Lu J , Delpire E ( 2002 ) Cation chloride cotransporters interact with the stress-related kinases Ste20-related proline-alanine-rich kinase (SPAK) and oxidative stress response 1 (OSR1) . J Biol Chem 277 : 50812 - 50819 .
9. Yang SS , Morimoto T , Rai T , Chiga M , Sohara E , et al. ( 2007 ) Molecular pathogenesis of pseudohypoaldosteronism type II: generation and analysis of a Wnk4(D561A/+) knockin mouse model . Cell Metab 5 : 331 - 344 .
10. Bjorklund M , Taipale M , Varjosalo M , Saharinen J , Lahdenpera J , et al. ( 2006 ) Identification of pathways regulating cell size and cell-cycle progression by RNAi . Nature 439 : 1009 - 1013 .
11. Tu SW , Bugde A , Luby-Phelps K , Cobb MH ( 2011 ) WNK1 is required for mitosis and abscission . Proc Natl Acad Sci U S A 108 : 1385 - 1390 .
12. Sun X , Gao L , Yu RK , Zeng G ( 2006 ) Down-regulation of WNK1 protein kinase in neural progenitor cells suppresses cell proliferation and migration . J Neurochem 99 : 1114 - 1121 .
13. Zambrowicz BP , Abuin A , Ramirez-Solis R , Richter LJ , Piggott J , et al. ( 2003 ) Wnk1 kinase deficiency lowers blood pressure in mice: a gene-trap screen to identify potential targets for therapeutic intervention . Proc Natl Acad Sci U S A 100 : 14109 - 14114 .
14. Xie J , Wu T , Xu K , Huang IK , Cleaver O , et al. ( 2009 ) Endothelial-specific expression of WNK1 kinase is essential for angiogenesis and heart development in mice . Am J Pathol 175 : 1315 - 1327 .
15. Gordon RD ( 1986 ) Syndrome of hypertension and hyperkalemia with normal glomerular filtration rate . Hypertension 8 : 93 - 102 .
16. Berger J , Senti KA , Senti G , Newsome TP , Asling B , et al. ( 2008 ) Systematic identification of genes that regulate neuronal wiring in the Drosophila visual system . PLoS Genet 4 : e1000085 .
17. Lawrence PA , Johnston P ( 1986 ) Methods of marking cells . In: Roberts DB, editor. Drosophila: A Practical Approach . Oxford: IRL Press. pp. 229 - 242 .
18. Sato A , Kojima T , Ui-Tei K , Miyata Y , Saigo K ( 1999 ) Dfrizzled-3, a new Drosophila Wnt receptor, acting as an attenuator of Wingless signaling in wingless hypomorphic mutants . Development 126 : 4421 - 4430 .
19. Fowles LF , Bennetts JS , Berkman JL , Williams E , Koopman P , et al. ( 2003 ) Genomic screen for genes involved in mammalian craniofacial development . Genesis 35 : 73 - 87 .
20. Ohnishi E , Goto T , Sato A , Kim MS , Iemura S , et al. ( 2010 ) Nemo-like kinase, an essential effector of anterior formation, functions downstream of p38 mitogen-activated protein kinase . Mol Cell Biol 30 : 675 - 683 .
21. Huang HS , Matevossian A , Whittle C , Kim SY , Schumacher A , et al. ( 2007 ) Prefrontal dysfunction in schizophrenia involves mixed-lineage leukemia 1- regulated histone methylation at GABAergic gene promoters . J Neurosci 27 : 11254 - 11262 .
22. Zhang Y , Cardell LO , Adner M ( 2007 ) IL-1beta induces murine airway 5- HT2A receptor hyperresponsiveness via a non-transcriptional MAPK-dependent mechanism . Respir Res 8 : 29 .
23. Xu B , Hua J , Zhang Y , Jiang X , Zhang H , et al. ( 2011 ) Proliferating cell nuclear antigen (PCNA) regulates primordial follicle assembly by promoting apoptosis of oocytes in fetal and neonatal mouse ovaries . PLoS One 6 : e16046 .
24. Leiserson WM , Harkins EW , Keshishian H ( 2000 ) Fray, a Drosophila serine/ threonine kinase homologous to mammalian PASK, is required for axonal ensheathment . Neuron 28 : 793 - 806 .
25. Curtiss J , Heilig JS ( 1995 ) Establishment of Drosophila imaginal precursor cells is controlled by the Arrowhead gene . Development 121 : 3819 - 3828 .
26. Curtiss J , Heilig JS ( 1997 ) Arrowhead encodes a LIM homeodomain protein that distinguishes subsets of Drosophila imaginal cells . Dev Biol 190 : 129 - 141 .
27. Grigoriou M , Tucker AS , Sharpe PT , Pachnis V ( 1998 ) Expression and regulation of Lhx6 and Lhx7, a novel subfamily of LIM homeodomain encoding genes, suggests a role in mammalian head development . Development 125 : 2063 - 2074 .
28. Matsumoto K , Tanaka T , Furuyama T , Kashihara Y , Mori T , et al. ( 1996 ) L3, a novel murine LIM-homeodomain transcription factor expressed in the ventral telencephalon and the mesenchyme surrounding the oral cavity . Neurosci Lett 204 : 113 - 116 .
29. Zagorska A , Pozo-Guisado E , Boudeau J , Vitari AC , Rafiqi FH , et al. ( 2007 ) Regulation of activity and localization of the WNK1 protein kinase by hyperosmotic stress . J Cell Biol 176 : 89 - 100 .
30. Zhao Y , Marn O , Hermesz E , Powell A , Flames N , et al. ( 2003 ) The LIMhomeobox gene Lhx8 is required for the development of many cholinergic neurons in the mouse forebrain . Proc Natl Acad Sci U S A 100 : 9005 - 9010 .
31. Mori T , Yuxing Z , Takaki H , Takeuchi M , Iseki K , et al. ( 2004 ) The LIM homeobox gene, L3/Lhx8, is necessary for proper development of basal forebrain cholinergic neurons . Eur J Neurosci 19 : 3129 - 3141 .
32. Manabe T , Tatsumi K , Inoue M , Matsuyoshi H , Makinodan M , et al. ( 2005 ) L3/Lhx8 is involved in the determination of cholinergic or GABAergic cell fate . J Neurochem 94 : 723 - 730 .
33. Fujita SC , Zipursky SL , Benzer S , Ferrus A, Shotwell SL ( 1982 ) Monoclonal antibodies against the Drosophila nervous system . Proc Natl Acad Sci U S A 79 : 7929 - 7933 .
34. Zipursky SL , Venkatesh TR , Teplow DB , Benzer S ( 1984 ) Neuronal development in the Drosophila retina: monoclonal antibodies as molecular probes . Cell 36 : 15 - 26 .
35. Luo L , Liao YJ , Jan LY , Jan YN ( 1994 ) Distinct morphogenetic functions of similar small GTPases: Drosophila Drac1 is involved in axonal outgrowth and myoblast fusion . Genes Dev 8 : 1787 - 1802 .
36. Lenertz LY , Lee BH , Min X , Xu BE , Wedin K , et al. ( 2005 ) Properties of WNK1 and implications for other family members . J Biol Chem 280 : 26653 - 26658 .
37. Fragkouli A , van Wijk NV , Lopes R , Kessaris N , Pachnis V ( 2009 ) LIM homeodomain transcription factor-dependent specification of bipotential MGE progenitors into cholinergic and GABAergic striatal interneurons . Development 136 : 3841 - 3851 .
38. Flandin P , Zhao Y , Vogt D , Jeong J , Long J , et al. ( 2011 ) Lhx6 and Lhx8 coordinately induce neuronal expression of Shh that controls the generation of interneuron progenitors . Neuron 70 : 939 - 950 .
39. Kahle KT , Wilson FH , Lalioti M , Toka H , Qin H , et al. ( 2004 ) WNK kinases: molecular regulators of integrated epithelial ion transport . Curr Opin Nephrol Hypertens 13 : 557 - 562 .
40. Shibaguchi T , Kato J , Abe M , Tamamura Y , Tabata MJ , et al. ( 2003 ) Expression and role of Lhx8 in murine tooth development . Arch Histol Cytol 66 : 95 - 108 .
41. Denaxa M , Sharpe PT , Pachnis V ( 2009 ) The LIM homeodomain transcription factors Lhx6 and Lhx7 are key regulators of mammalian dentition . Dev Biol 333 : 324 - 336 .
42. Fragkouli A , Hearn C , Errington M , Cooke S , Grigoriou M , et al. ( 2005 ) Loss of forebrain cholinergic neurons and impairment in spatial learning and memory in LHX7-deficient mice . Eur J Neurosci 21 : 2923 - 2938 .