Regulation of sperm activation in C. elegans - 1 Cell differentiation is accompanied by morphological changes and driven by differential
2 gene expression through transcriptional and post-transcriptional mechanisms. In the post-
3 meiotic spermatids, however, transcription is repressed, and yet the spermatids need to
4 undergo morphological changes to gain motility and fertilization competence. This process,
5 called spermiogenesis, depends on post-transcriptional mechanisms. As an extreme example,
6 spermiogenesis in the nematode C. elegans (also called sperm activation), takes place rapidly
7 and is independent of both transcription and new protein synthesis. This process transforms
8 spherical spermatids into polarized and motile spermatozoa with pseudopods and allows the
9 sperm to be fertilization competent. How the spermatids sense and process the signals to
10 initiate spermiogenesis is not well understood. The nematode C. elegans exist primarily as self-
11 fertilizing hermaphrodites, and males that can mate with hermaphrodites. Sperm activation is
12 initiated by independent but converging signaling pathways in hermaphrodites versus males.
13 These pathways involve secreted proteases, transmembrane proteins, kinases, iron
14 transporters, and other effector proteins. Not all the genetic regulators are known; how these
15 regulators work together to induce cellular changes during activation is not well understood. The
16 long-term goal of this application is to understand the genetic regulation of gamete development
17 and gamete functions. The proposed work here takes advantages of unique mutant alleles
18 isolated in a forward mutant screening for genes that regulate gamete function during
19 fertilization. Two temperature-sensitive mutant alleles, as47 and as48, both show a sharp drop
20 in fertility and defects in sperm activation in vitro. The allele as47 affects a gene encoding a
21 Ser/Thr protein phosphatase. The objective of this application is to investigate the molecular
22 mechanism of the regulation of sperm activation by phosphatases and to identify additional
23 regulators. This objective will be broken down to three aims: 1), investigate the mechanisms by
24 which the affected phosphatase in as47 regulates sperm activation. 2), investigate the role of a
25 related Ser/Thr phosphatase in sperm activation. In both aim 1 and 2, genetic analyses and a
26 cellular biological approach will be used to dissect the relationship between these phosphatases
27 and known pathways of sperm activation. 3), identify and explore the function of the gene
28 affected in as48. This proposed work will lead to a better understanding of the genetic regulation
29 of sperm development/differentiation. The knowledge gained from this application will be
30 applicable to other developmental contexts and to high-order organisms.
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