To explore how chromosomes prepare for the meiotic divisions, we are examining the function of the C. elegans Myt1 ortholog. Myt1 belongs to the Wee1 family of kinases and is thought to down regulate Cdk1 during the cell cycle. RNAi studies with the Myt1 ortholog, wee-1.3, result in infertility. Mothers injected with dsRNA quickly become infertile;the oocyte chromosomes are no longer paused in diakinesis of meiosis I. These chromosomes have many hallmarks of being mitotic;they stain with a number of mitotic marker antibodies. Oocyte maturation also appears to be precocious. We propose that WEE-1.3 normally functions to keep maternal CDK-1 inactive during oogenesis, and that upon fertilization, CDK-1 becomes activated to allow for the meiotic and mitotic divisions of the embryo. In the absence of WEE-1.3, CDK-1 becomes precociously active and drives oocyte maturation and chromosome maturation in immature oocytes that are not fully differentiated. These oocytes fail to be fertilized presumably because they have not synthesized all the proper oocyte/embryo products they need for further development or because they have precociously triggered their block to polyspermy. We have recently constructed and expressed transgenes coding for WEE-1.3::GFP fusion proteins. These transgenes are expressed in the germline and nuclear envelope and will be useful for identifying mutants that perturb this expression pattern. These GFP transgenes also rescue a wee-1.3 deletion mutant. To determine genes that interact with wee-1.3, we performed an RNAi suppressor screen utilizing 1874 embryonic lethal clones from the OpenBiosystems RNAi library. From this screen we identified 149 genes that when co-depleted with wee-1.3 result in a restoration of fertility. We have confirmed the identity of these suppressor genes and begun to characterize the mechanisms through which they suppress the sterility of wee-1.3 RNAi utilizing both RNAi approaches and available mutants. The strength of this approach is its potentiality for identifying novel components of both the cell cycle and oocyte meiotic maturation. We are currently focusing on the characterization of two specific genes that have been implicated in human disease, but that have not been previously known to function during oocyte maturation or germline development.
