CAREER: Investigating Mechanisms of Histone Variant Function and Regulation that Affect Transcriptional Control and fertility in C. Elegans

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Investigating mechanisms of a sperm-specific histone variant in transcriptional regulation important for fertility in C. elegans sperm are formed during a period where extreme changes in chromatin architecture are coupled with dynamic shifts in gene expression. Differentiation of pluripotent germ cells into mobile sperm requires transcriptional regulation of specific genes. Simultaneously, sperm nuclear basic proteins, such as histone variants, replace somatic histones to achieve tightly compacted sperm DNA. In preliminary studies, the first known C. elegans sperm nuclear basic protein, a histone H2A variant called HTAS-1, was identified and found to be required for optimal fertility. Preliminary data from DNA microarray analyses identified both activated and repressed genes in htas-1 mutants compared with wild-type animals. Strikingly, genes that are activated in htas-1 mutants function in forming germ cells via gamete formation progression, oocyte maturation, ovulation, sperm signaling, and sperm migratory behavior. Therefore, the central hypothesis of this project is that HTAS-1 incorporation modulates the expression of genes that work in concert for optimal fertility in sperm. To test this, germ cell progression, oocyte development, and sperm behavior will be assessed to determine how each contributes to reduced fertility in htas-1 mutants. To identify direct targets of HTAS-1 transcriptional regulation, Dr. Chu and her colleagues will define sites of HTAS-1 incorporation during sperm development using chromatin immunoprecipitation and DNA microarray analysis. To elucidate how HTAS-1 both activates and represses transcription, characterization of PTMs on HTAS-1 will be initiated using mass spectrometry to understand how HTAS-1 function is regulated at gene targets. The research in this CAREER project is significant because it elucidates mechanisms of transcriptional regulation through incorporation of a sperm-specific histone variant that functions in a conserved developmental process, sperm production.The project will define evolutionarily conserved mechanisms that regulate how changes in DNA packaging alter the expression of genes important for sperm formation. It has important and broad impact because it contributes to the career development of underrepresented minority and female students at San Francisco State University, an undergraduate minority-serving institution. To boost both basic and scientific writing skills in multicultural students, Dr. Chu will develop a graduate course in scientific proposal writing that is coordinated with tutoring in basic writing skills through collaboration with the English Department and Learning Assistance Center at SFSU. Thus the project integrates the participation of students into basic research on chromatin biology and reproduction and also provides resources to help promote their long-term professional development in science.