Spermatid Cyst Polarization in Drosophila Depends upon apkc and the CPEB Family Translational Regulator orb2
Schedl P (2014) Spermatid Cyst Polarization in Drosophila Depends upon apkc and the CPEB Family Translational Regulator orb2. PLoS
Genet 10(5): e1004380. doi:10.1371/journal.pgen.1004380
Spermatid Cyst Polarization in Drosophila Depends upon apkc and the CPEB Family Translational Regulator orb2
Shuwa Xu 0
Sanjay Tyagi 0
Paul Schedl 0
Eli Arama, Weizmann Institute of Science, Israel
0 1 Department of Molecular Biology, Princeton University , Princeton , New Jersey, United States of America, 2 Public Health Research Institute, New Jersey Medical School, Rutgers University , Newark , New Jersey, United States of America, 3 Institute of Gene Biology, RAS , Moscow , Russia
Mature Drosophila sperm are highly polarized cells-on one side is a nearly 2 mm long flagellar tail that comprises most of the cell, while on the other is the sperm head, which carries the gamete's genetic information. The polarization of the sperm cells commences after meiosis is complete and the 64-cell spermatid cyst begins the process of differentiation. The spermatid nuclei cluster to one side of the cyst, while the flagellar axonemes grows from the other. The elongating spermatid bundles are also polarized with respect to the main axis of the testis; the sperm heads are always oriented basally, while the growing tails extend apically. This orientation within the testes is important for transferring the mature sperm into the seminal vesicles. We show here that orienting cyst polarization with respect to the main axis of the testis depends upon atypical Protein Kinase C (aPKC), a factor implicated in polarity decisions in many different biological contexts. When apkc activity is compromised in the male germline, the direction of cyst polarization within this organ is randomized. Significantly, the mechanisms used to spatially restrict apkc activity to the apical side of the spermatid cyst are different from the canonical cross-regulatory interactions between this kinase and other cell polarity proteins that normally orchestrate polarization. We show that the asymmetric accumulation of aPKC protein in the cyst depends on an mRNA localization pathway that is regulated by the Drosophila CPEB protein Orb2. orb2 is required to properly localize and activate the translation of apkc mRNAs in polarizing spermatid cysts. We also show that orb2 functions not only in orienting cyst polarization with respect to the apical-basal axis of the testis, but also in the process of polarization itself. One of the orb2 targets in this process is its own mRNA. Moreover, the proper execution of this orb2 autoregulatory pathway depends upon apkc.
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Funding: PS would like to acknowledge support by NIH grant GM043432. PS would also like to acknowledge support from a grant to the Gene Biology Institute
by the Russian Federation Ministry of Education and Science (14.B25.31.0022). ST would like to acknowledge support from the NIH grant AI106036. The funders
had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
Polarity plays a central role in a diverse array of biological
contexts in organisms ranging from single cell bacteria to complex
multicellular eukaryotes. In multicellular eukaryotes, the steps
involved in establishing, maintaining, and transmitting polarity are
typically controlled by an interacting set of evolutionarily
conserved atypical protein kinase C-partitioning defective proteins
(aPKC-PAR proteins). The classic model for polarity
determination by the aPKC-PAR machinery is the establishment of the
anterior-posterior axis in the C. elegans embryo [1]. Prior to
fertilization, anterior determinants, the worm aPKC ortholog
PKC-3, PAR-3 and PAR-6, are distributed in a complex around
the entire cortex of the egg [24], while the posterior factors,
PAR1 and PAR-2, are cytoplasmic. PAR-2 is kept off the cortex by
PKC-3 dependent phosphorylation, and a similar mechanism may
apply to PAR-1 [5,6]. Sperm entry induces a cytoplasmic flux that
relocalizes the PKC-3/PAR-3/PAR-6 complex in the posterior to
the anterior cortex. Following the removal of PKC-3 activity from
the posterior, PAR-1 and PAR-2 are able to associate with the
cortex. Cortical PAR-2 in turn prevents re-association of anterior
determinants with the posterior cortex (for review: [7]). This
generates a polarized cell in which the PKC-3/PAR-3/PAR-6
complex is distributed along the anterior cortex, while PAR-1/
PAR-2 are localized on the posterior cortex. This process also
serves to orient the mitotic spindle: the first cell division in the
embryo is parallel to the anterior-posterior axes and as a
consequence the two daughter cells receive different sets of
embryonic determinants [1]. The aPKC-PAR machinery defines
polarity in many other contexts besides the establishment of the
anterior-posterior axis of the C.elegans embryo. Moreover, as in
C.elegans, a (...truncated)