COMPARATIVE EPIDIDYMAL PROTEOME OF MONOTREMES AND OTHER MAMMALS INCLUDING HUMANS

Abstract

The two epididymal functions preserved across mammalian species are the maturation of the testicular sperm in the proximal epididymis and the maintenance of their viability in the distal part of this organ. There is a division of labour along the epididymis to carry out these functions involving sequential modification of the composition of the luminal milieu in numerous regions by the secretion and absorption of specific proteins. We are examining the protein composition of the epididymal fluids in order to identify which proteins have been conserved during mammalian evolution. This report presents an analysis of the epididymal proteome and secretome on several domestic mammals, monotreme and human. Using a microcannulation technique, the proteins present and secreted in the lumen fluid by the epithelium from various epididymal regions were analysed and identified by 2D gel electrophoresis and LC MS/MS from all these different species. Several hundred epididymal proteins were identified and for several of them, their luminal concentrations along the epididymal tube were quantified. Among these most distant species in mammalian evolution, several proteins or protein functionalities have been conserved, although their abundance in the epididymal luminal fluid varies considerably between species. Further, the variation among species in the secretory activity and luminal protein composition along the epididymis indicates that the regionalisation of the epididymides is specific to species, although it is small among the monotremes. The monotreme and human epididymides show the least regionalization in the luminal composition and the secretion of protein. This comparative approach illustrates that evolution has produced different strategies of providing a protein environment for sperm maturation and storage in the epididymis.