Sequence of sperm cell surface differentiation and its relationship to exogenous fluid proteins in the ram epididymis

To study successive surface changes of maturing ram spermatozoa, we determined the 125I-labeling patterns of testicular spermatozoa and of spermatozoa from 10 consecutive regions of the epididymis. Overall, three phases of cell surface transformations are distinguishable: Phase I occurs in the caput epididymidis and it is characterized by a series of rapid surface changes. The most striking surface transformations occur during transport of spermatozoa from the testis into the proximal caput epididymidis. All major surface components in the zones 78 to 115 kd disappear or are lost from the surface of testicular spermatozoa. Concurrently, several low molecular weight components (17 to 65 kd) appear or become increasingly accessible to 125I. Phase II represents a period of relative quiescence which is confined to the corpus epididymidis. Phase III takes place in the cauda epididymidis where several existing (97, 65 and 41 kd) and new (24 kd) proteins become the predominant features of the sperm cell surface. Electrophoretic analyses of luminal fluid proteins from corresponding regions of the testis and epididymis also show that the most striking changes occur between the rete testis and the proximal caput epididymidis. No rete testis fluid (RTF) components are detectable in luminal fluid of the proximal caput epididymidis. In the epididymis, however, fluid proteins are more persistent than sperm surface components. Several major fluid components (i.e., 95, 76, 21.5, 19.5 and 16 kd) persist throughout the epididymis. Other fluid proteins are of a more transient nature as, for example, a 25 kd molecular weight component (regions E1 through E6) or the 180, 62, 37 and 32 kd components in regions E4 to E10, the 270, 115 and 105 kd proteins in regions E6 to E10 and the 360, 145, 125 and 62 kd molecular weight components in regions E7 to E10. No direct relationships could be established between intrinsic surface components and exogenous fluid proteins from corresponding regions of the testis and epididymis. These results demonstrate a much greater complexity of sequential surface transformation in maturing epididymal spermatozoa than was predictable from our earlier studies of testicular and ejaculated spermatozoa. Apparently, ram spermatozoa must undergo extensive surface renovations in the caput epididymidis before the surface protein pattern typical of mature spermatozoa slowly develops.