smz-1 is a suppressor of memi-1(sb41) implicated in spermatogenesis and embryonic viability 
Creators: Daher, Rim
Publisher: name: University of Alberta Library
Year: 2024

<p>In most sexually reproducing organisms, gametic cells fuse via a process known as fertilization. However, in many organisms, the female gamete does not complete the final meiotic cell division until after fertilization. It is still unclear how fertilization triggers the completion of female meiosis, and how the subsequent transition to embryonic development is orchestrated. In Caenorhabditis elegans, fertilization is required for completion of the female meiosis I (MI) division, and entry into meiosis II (MII). The Srayko lab discovered three paralogous genes, memi-1/2/3 (meiosis-to-mitosis) that are, together, required for completion of MI and entry into MII. The memi genes encode oocyte proteins that are likely involved in the sperm-derived signal required for MII, but they are normally degraded soon after the fertilized oocyte enters MII. A hypermorphic, gain-of-function mutation, memi-1(sb41) results in the persistence of MEMI-1 protein, which causes severe MII delays that eventually result in embryonic death. This suggests that MEMI must also be degraded to allow the transition from MII to embryonic mitosis. Previously, gsp-4 and gskl-1/2 were identified as suppressors of memi-1(sb41) using genome-wide RNAi and EMS-based suppressor screens. Interestingly, these genes encode sperm proteins that are essential for processes pertaining to male meiosis, spermatogenesis, and sperm motility.<br>
In this study, I report the identification of smz-1 as a suppressor of memi-1(sb41). smz-1 (sperm meiosis PDZ domain containing protein) and its paralog, smz-2, encode proteins previously reported to play a role in spermatogenesis (Chu et al., 2006). However, little is known about their mechanism of action. The suppressor mutation, smz-1(abc53) is predicted to cause a I32N change to the amino acid sequence.<br>
Work presented in this thesis provides evidence that smz-1-based suppression of memi-1(sb41) acts in a hermaphrodite-sperm-specific manner. This result is different from known sperm-specific suppressors identified thus far, which all suppressed memi-1(sb41) by outcrossing to males mutant for the suppressor. This suggests that smz-1-based suppression is part of a novel mechanism. Interestingly, the I32N mutation suppresses memi-1(sb41) much better than either smz-1 or smz-2 deletion mutants, which reveals that the I32N mutation might not be a simple loss-of-function allele. I observed that smz-1; smz-2 double-deletion hermaphrodites are self-sterile, indicating that smz-1 and smz-2 genes are essential for sperm production, similar to previous reports based on RNA-mediated interference experiments. This phenotype was rescued by outcrossing to wild-type males, suggesting that smz-1/2 functions are restricted to the sperm. Genetic combinations between smz-1 and other sperm-specific suppressors of memi-1(sb41), gskl-1 or its paralog gskl-2, revealed a synthetic enhancement whereby the double and triple mutant strains exhibit decreasing brood sizes and a higher percentage of embryonic lethality. This result indicated that smz-1 likely acts within the same pathway as gskl-1/2 for both sperm and embryonic functions. Similar experiments with gsp-4 did not show enhancement, revealing a possible separation of function for smz-1 with respect to these genes. All together, these results identified smz-1 and smz-2 as new sperm components involved in the MEMI pathway.</p>