Exit from meiotic prophase into the division phase must be precisely timed and coordinated. If it is either too early or too late, with inappropriate resolution of recombination events, it is likely to result in failure of homologs to separate (nondisjunction). The resulting gametic aneuploidy leads to infertility, pregnancy loss, or birth defects, all serious consequences of getting this crucial step of meiosis wrong. This project will focus on the mechanisms ensuring a timely exit from meiotic prophase. Successfully exiting meiotic prophase and executing this transition requires a set of coordinated responses to signals indicating that chromosome synapsis and genetic recombination have been completed. Evidence suggests these signals are integrated at the level of the synaptonemal complex (SC). Our work 1) shows that competency for meiotic prophase exit arises after assembly of the SC, 2) provides evidence for interactions among the proteins we will investigate in this project, and 3) reveals the importance of events at the SC in initiating transition from prophase to the divisio phase. Based on our findings, we propose a regulatory network whereby SC-associated proteins SMC5/6 and HSPA2 are essential components in an exiting mechanism activating PLK1, an effector kinase that initiates desynapsis. We will test this model using both genetic and cellular approaches to answer two critical questions: What proteins at the SC are involved in signaling onset of meiotic exit? What prompts desynapsis, the initial and key event of meiotic exit? In Aim 1, we will determine the meiotic role of the structural maintenance of chromosomes SMC5/6 complex by creating null mutations in genes encoding testis-specific kleisin subunit of the SMC5/6 complex, EID3, and SMC5, and by determining protein interactions.
In Aim 2, we will delineate mechanisms by which the SC-localized chaperone protein HSPA2 coordinates desynapsis and meiotic exit by determining its interacting kinase and SC protein partners. And in Aim 3, we will determine the genetic requirement for and interactions of the polo-like kinase PLK1, which our preliminary evidence suggests is a desynapsis kinase. These experimental strategies will test the signal transduction pathway by which the SC coordinates meiotic exit and identify mechanisms that ensure production of chromosomally normal gametes. Furthermore, two of the aims address proteins that are of broad significance in mitosis and cancer cell biology, the SMC5/6 complex and PLK1; thus these results will impact on mechanisms that regulate mitosis in the face of genomic damage.
Meiosis is a defining event of gametogenesis, the production of eggs and sperm, and ensures that each gamete has the right chromosome constitution. When this process fails in any way, the consequences are likely to be infertility, or production of aneuploid gametes possessing the wrong number of chromosomes, with resulting birth defects or failure of pregnancy. This project directly tests the function of key proteins that mitigate DNA damage and meiotic errors that cause aneuploidy. The results will help us determine mechanisms that ensure genomic integrity and the causes for some cases of human male meiotic 'maturation arrest' infertility.
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