Heterogeneity of epididymal spermatozoa of the hamster

Epididymal transit is involved in the acquisition of fertilizing ability by mammalian spermatozoa. The epididymis is implicated in the addition and/or modification of sperm surface proteins functionally involved in the processes leading to fertilization. In order to characterize these sperm components, we have studied the modifications of sperm membrane proteins during epididymal maturation. Hamster spermatozoa were collected from the caput, corpus, and proximal and distal cauda of the epididymis and submitted to a continuous Percoll gradient centrifugation. Independently of their epididymal origin, the spermatozoa were distributed into two bands of buoyant densities of 1,045 and 1,088 on the gradient. However, the proportion of more dense spermatozoa increased progressively along the epididymis. This proportion is 87-fold higher in the distal cauda compared to the caput. SDS-PAGE electrophoresis demonstrated that although they originate from different regions of the epididymis, spermatozoa of the same density exhibited similar membrane protein patterns. In contrast, the electrophoretic patterns of spermatozoa with densities of 1,045 and 1,088 were very different. One of these differences involves a 26 kD protein that is implicated in zona pellucida recognition (Sullivan and Bleau, Gamete Res 12:101-116, 1985). This protein is present in dense sperm obtained from all regions of the epididymis but is absent in spermatozoa of low density. If we consider that this 26 kD protein is a "marker" of surface changes occurring during sperm maturation, we can hypothesize that in the proximal segments of the epididymis a certain proportion of spermatozoa are indeed mature but that this proportion increases considerably along the epididymis.