SummaryIn all mammalian species, the final differentiation of the male germ cell occurs in the epididymal duct where the spermatozoa develop the ability to be motile and fertilize an ovum. Understanding of these biological processes is the key to understanding and controlling male fertility. Comparative studies between several mammals could be an informative approach to finding common sperm modifications which are not species-20 specific. The new global biological approaches such the transcriptomes and proteomes provide considerable information which can be used for such comparative approaches. This report summarizes our proteomic studies of the epididymis of several mammals, including humans.Introduction:

The acrosomal matrix (AM) is an insoluble structure within the sperm acrosome that serves as a scaffold controlling the release of AM-associated proteins during the sperm acrosome reaction. The AM also interacts with the zona pellucida (ZP) that surrounds the oocyte, suggesting a remarkable stability that allows its survival despite being surrounded by proteolytic and hydrolytic enzymes released during the acrosome reaction. To date, the mechanism responsible for the stability of the AM is not known. Our studies demonstrate that amyloids are present within the sperm AM and contribute to the formation of an SDS-and formic-acid-resistant core. The AM core contained several known amyloidogenic proteins, as well as many proteins predicted to form amyloid, including several ZP binding proteins, suggesting a functional role for the amyloid core in sperm-ZP interactions. While stable at pH 3, at pH 7, the sperm AM rapidly destabilized. The pH-dependent dispersion of the AM correlated with a change in amyloid structure leading to a loss of mature forms and a gain of immature forms, suggesting that the reversal of amyloid is integral to AM dispersion.A n essential step during fertilization is the sperm acrosome reaction (AR) in which the acrosome, an exocytotic vesicle overlying the sperm head, releases its contents, allowing the spermatozoon to penetrate the investments surrounding the oocyte. Point fusions between the outer acrosomal and plasma membranes result in membrane vesiculation, allowing the soluble contents to be released. The acrosome also includes an insoluble fraction called the acrosomal matrix (AM), which is defined as a membrane-free, electron-dense material that remains after spermatozoa are extracted with Triton X-100 (1). Functionally, the AM is thought to provide a stable scaffold that allows the controlled and sequential release of matrix-associated proteins during the AR, as well as to facilitate interactions between the sperm and oocyte (2, 3). While the mechanisms for the assembly and disassembly of the AM are not known, the self-assembly of proteins into a large complex has been proposed for its formation and disassembly is thought to be due to active proteases (1).The site of the AR has been controversial and was previously thought not to occur in the mouse until spermatozoa encounter the zona pellucida, the thick coat surrounding the oocyte (4, 5). However, recent studies with video imaging microscopy to follow individual mouse spermatozoa with enhanced green fluorescent protein expressed in their acrosomes showed that, in fact, the fertilizing spermatozoa underwent the AR much earlier during transit through the cumulus cells prior to encountering the zona pellucida (6). Further studies indicated that these acrosome-reacted spermatozoa remained capable of binding and penetrating the zona pellucida (7). Together, these studies suggest that the AM, instead of the soluble components of the acrosome, is required for binding and penetration of the zona pellucida. The presence of several zona pelluc...

The acquisition of the ability of the male gamete to fertilize an ovum is the result of numerous and sequential steps of differentiation of spermatozoa that occur as they transit from the testis to the end of the epididymal tubule. The post gonadal sperm modifications are mostly related to motility, egg binding, and penetration processes. As the activity of the epididymis and its luminal fluid composition are believed to be directly related to 'sperm maturation', a review on epididymal proteins is presented. Comparative studies have shown that the epididymal activities are species specific. Nevertheless, for all mammalian species studied, similarities exist in the sequential proteomic changes of the luminal composition of the epididymal tubule and proteins on the sperm surface. The potential roles of these modifications are discussed.