Comparative genomic and evolutionary analysis of sperm proteomes

Abstract

While the central role of spermatozoa in sexual reproduction and fertilization is well understood, many functional attributes of sperm have yet to be elucidated at the molecular level. One key to ultimately understand the molecular basis of sperm function is to comprehensively characterize its biochemical composition. This crucial information has been lacking, as molecular characterization of the sperm cell cannot be assessed by classic gene expression assays since mature spermatozoa are transcriptionaly inert. Whole-cell shotgun proteomic approaches have revolutionized the molecular analysis of sperm form and function. We have utilized improved methodologies to re-analyze the D. melanogaster sperm proteome and characterize five additional Drosophila species sperm proteomes. This methodology, which included a 1D SDS-PAGE prefractionation step, resulted in good reproducibility between biological replicates and high quality sperm proteomes. An interspecific analysis of the sperm proteomes revealed that despite variation in protein composition, Drosophila sperm proteomes have a consistent functional profile and 519 proteins were identified a being conserved across the melanogaster subgroup within a phylogenetic framework.Evolution of the sperm proteome was explored in Mus musculus through the utilization of targeted proteomic datasets completed, which provided subcellular localizations for sperm components. This study resulted in several novel findings, including evidence for accelerated evolution as well as an enrichment of positive selection on genes found in the cell membrane and acrosome. This may be a result of the selective pressures encountered by these membrane proteins during sperm development, maturation and transit through the female reproductive tract where the sperm cell membrane, and eventually the acrosome, are exposed to the extracellular milieu and are available for direct cell-cell interactions. These findings not only reveal the varying evolutionary pressures acting on a single cell type but also highlights the utility of the proteomics technique in clarifying protein interaction and evolutionary history.

Date of Award	1 Apr 2011
Original language	English
Awarding Institution	University of Bath
Supervisor	Stephen Dorus (Supervisor) & Timothy Karr (Supervisor)