Meiosis is the specialized form of cell division that generates haploid gametes from diploid precursors. It is essential for the life-cycles of almost all eukaryotic organisms. Understanding meiotic regulatory mechanisms is relevant to human health since defects in meiosis cause infertility, cancer, and birth defects. Baker's yeast is an outstanding model system to study meiotic development. In response to starvation, diploid cells enter meiotic development and generate four haploid cells within the mother cell. Early events include meiotic DNA replication, homolog pairing, and genetic recombination. After the completion of genetic recombination, cells undergo 2 rounds of chromosome segregation without an intervening S-phase. After the second meiotic division (MII), the haploid products are encased in spore walls that protect the haploids from environmental insults. Although yeast has taught us much about meiotic S-phase, prophase, and the meiotic divisions, much less is known about the processes that occur after MII has taken place. One reason we know so little about the post-meiotic phase of this program is that the spore walls are experimentally impenetrable; extracting macromolecules under native conditions or monitoring molecules using immunofluorescence methods has until recently been nearly impossible. Previous work in the sponsor's laboratory has identified a meiosis-specific MAPK named Smk1 that controls the post-meiotic program of spore formation. This led to the discovery that Smk1 activates the expression of late meiosis-specific genes, which are uniquely expressed after the spore wall has assembled. This proposal takes advantage of engineered yeast strains that produce permeable spore walls so that the intracellular and nuclear events that occur during the late stages of meiotic development can be studied. The proposal also takes advantage of engineered forms of Smk1 that are sensitive to cell-permeable purine analogs (smk1-as) that can be used to turn Smk1 on and off. Mutations that permeabilize the spore wall with smk1-as are combined in a genetic background that undergoes meiosis in a highly synchronous manner, and this will be used to define the complete set of late meiosis-specific genes that are regulated by Smk1 (aim 1). We will also test the hypothesis that Smk1 is recruited to late meiosis-specific transcriptional promoters (aim 2). Preliminary data suggests that Smk1 phosphorylates the C terminal domain of RNA polymerase, and we will also test this hypothesis and whether these modifications take place at late meiosis specific genes as they are being transcribed (aim 3). Studies of how meiotic events are regulated in yeast may provide insights into human gametogenesis, which have clinical implications in solving infertility, miscarriages, and developmental disorders. The principal investigator (Julia Lee-Soety) intends to conduct this work during her sabbatical leave in Dr. Edward Winter's laboratory at the Thomas Jefferson University in Philadelphia. Beyond the project period, the PI plans to continue follow-up studies with undergraduate research students at her home institution (Saint Joseph's University).
Meiosis is a multi-step, highly ordered process in which diploid cells form haploid cells. Understanding meiotic development is relevant to solving human infertility, spontaneous abortions, and developmental disorders. The work proposed in this application will uncover new regulatory mechanisms that control meiosis and provide training to pursue independent research on meiotic development using the well-established yeast model system.
