The specificity of epididymal secretory proteins

Early studies in which the electrophoretic profiles of fluid from different regions of the epididymis were compared with other body fluids, such as blood serum, suggested that many proteins present in epididymal fluid were not found in other secretions and thus might be tissue specific. Comparative studies of epididymal fluid from different species further emphasized differences so that some epididymal proteins are considered both tissue and species specific. Such proteins are the putative molecular agents responsible for the array of changes undergone by spermatozoa during maturation. Thus a complete characterization of all the specific proteins secreted by the epididymis would yield important information for understanding the molecular events of maturation. Comparison of these proteins across species would determine whether the proteins and mechanisms at the centre of changes such as acquisition of fertilizing ability are conserved during evolution. This review critically examines the evidence for both tissue and species specificity of epididymal secreted proteins, describes how advances in molecular biology can be used to clarify this issue and concludes with a description of some preliminary work with different lagomorph species involving the REP 52 protein, an epididymal secretory protein that binds specifically to spermatozoa in New Zealand white rabbits.