Fine Mapping of a Degenerated Abdominal Legs Mutant (Edl) in Silkworm, Bombyx mori
January
Fine Mapping of a Degenerated Abdominal Legs Mutant (Edl) in Silkworm, Bombyx mori
Honglei Wang☯ 0 1 2
Xiaoling Tong☯ 0 1 2
Meijing Liu 0 1 2
Hai Hu 0 1 2
Zhiquan Li 0 1 2
Zhonghuai Xiang 0 1 2
Fangyin Dai 0 1 2
Cheng Lu 0 1 2
☯ These authors contributed equally to this work. 0 1 2
0 1 2
0 1 2
0 State Key Laboratory of Silkworm Genome Biology, Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University , Chongqing , China
1 Research and Development 863 Program of China Grant (No. 2013AA102507) , National Natural Science Foundation of China (No. 31472153, No. 30901053 and No. 31372379) , Fundamental Research Funds for the Central Universities in
2 Editor: Erjun Ling, Institute of Plant Physiology and Ecology Shanghai Institutes for Biological Sciences , CHINA
In insects, abdominal appendages, also called prolegs, vary due to adaptive evolution. Mutations on prolegs within species provide insights to better understand the mechanisms underlying appendage development and diversity. In silkworm Bombyx mori, extra-crescents and degenerated abdominal legs (Edl) mutant, belonging to the E pseudoallele group, is a spontaneous mutation that adds crescents and degenerates prolegs on the third abdominal segment (A3). This mutation may be a homeotic transformation of A3 to A2. In this study, the Edl locus was mapped within approximately a 211 Kb region that is 10 Kb upstream of Bmabdominal-A (Bmabd-A). RT-quantitative PCR (RT-qPCR) and Western blot analysis of Bmabd-A expression showed a slight but significant decrease, while the expression of BmUltrabithorax (BmUbx) was up-regulated in the Edl mutant compared to wildtype (Dazao). Moreover, we also found that BmDistal-less (BmDll), which regulated the development of distal proleg structures, was missing at the tips of the A3 prolegs in the Edl mutant compared to BmDll expression in normally developed prolegs in both the wildtype and mutant. Collectively, we identified approximately a 211 Kb region in the Edl locus that regulates BmUbx and Bmabd-A expression and found that changes in BmUbx and BmabdA expression may lead to the loss of distal proleg structures in B. mori.
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Copyright: © 2017 Wang et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which
permits unrestricted use, distribution, and
reproduction in any medium, provided the original
author and source are credited.
Data Availability Statement: Most relevant data
are within the paper and its Supporting Information
files, and other relevant data are available from the
NCBI database (accession numbers
KX344456KX344459).
Introduction
Morphological characteristics of insects are surprisingly variable. Particularly, the appendage
number, morphology and position vary largely within and between species. Studies on the
mechanisms underlying appendage development and diversity provide insights into the
evolutionary process of arthropods [1±3].
Each thoracic segment, on the ventral side of an insects' trunk, contains appendages called
thoracic legs. The appendages on the abdominal segments are known as prolegs and their
numbers vary markedly [
4
]. Segmental identities of these legs are determined by several
Homeotic genes [
5
], which consist of a tandem gene cluster where the order of genes is
co-linear with their expression pattern on the body axis [
6
]. The development of prolegs is mainly
China (No. XDJK2013A001), and Chongqing Youth
Science and Technology Talent Training Project
(cstc2014kjrc-qnrc80001). The funders had no role
in study design, data collection and analysis,
decision to publish, or preparation of the
manuscript.
regulated by Ultrabithorax (Ubx) and abdominal-A (abd-A). For example, in the dipteran,
Drosophila melanogaster, abdominal-B (abd-B), abd-A and Ubx repress proleg development [7±9]; in
the flour beetle, Tribolium castaneum, Ubx does not repress but modifies the morphology of
prolegs on abdomen 1 (A1), abd-A represses the development of proleg on the posterior abdominal
segments [
10
]; in the lepidopteran, Manduca sexta, Ubx represses the development of prolegs on
the anterior abdomen, but abd-A does not repress the development of prolegs because robust
expression of abd-A is found in proleg primordia of A3-A6, which develop into prolegs [
11
].
Finally, in the lepidopteran, Bombyx mori, BmUbx and Bmabd-B repress the development of
prolegs on the anterior and posterior abdominal segments, respectively; Bmabd-A, on the other
hand, is known to play an important role in the development of prolegs on the intermediate
abdominal segments, and RNAi of Bmabd-A results in the deletion of prolegs [12±17].
Studies in Drosophila have shown that the bithorax complex (BX-C) contains many
cis-regulatory elements and some non-protein coding transcripts, which work together to control
neighboring Hox gene expression [18±20]. The cis-regulatory elements are organized (...truncated)