Chromatin and the Control of Late Meiotic Gene Expression

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Gametogenesis requires cells to exit from mitosis and undergo the modified cell division program of meiosis to produce differentiated gametes. The shift from mitosis to meiosis and differentiation requires the rewiring of important regulatory circuits in the cell. Sporulation in yeast is a tractable model system in which to study these events. As yeast cells complete meiosis and form spores (gametes) specific histone modifications occur and similar modifications have been reported during gametogenesis in metazoans. Using chromatin immunoprecipitation in combination with tiling microarrays, the distribution of these modified histiones in the chromatin will be defined. Also, the function of these changes with respect to the will be analyzed by phenotypic characterization of spores lacking the modifications and by use of a microscopic assay to assess chromatin condensation in wild-type and mutant spores. Transcription of genes late in sporulation must take place in this altered chromatin context. The interplay between chromatin and a transcription factor necessary for late gene expression will be explored. Meiosis and sporulation occur in response to environmental cues, similar to differentiation in higher cells. Also similar to higher cells, as yeast enter meiosis they pass a commitment point after which, even if the inducing signals are lost or reversed, they nevertheless complete sporulation. As part of this commitment process, the expression of a set of genes important for spore formation becomes insulated from changes in external signals. We will test the hypothesis that these insulated genes represent an autoregulatory gene set and investigate the molecular basis for the insulation of these genes. Whether insulation occurs at the level of transcription or RNA stability will be determined, the cis-acting sequences responsible for insulation will be defined and the protein(s) binding to these seqeunces will be identified.