Analysis of surface proteins of rat spermatozoa during epididymal transit and identification of antigens common to spermatozoa, rete testis fluid and cauda epididymal plasma

Abstract

Summary. Spermatozoa from the testis and cauda epididymidis of the rat were surface labelled with radioactive iodide, extracted with detergent, and the radioactive proteins separated by two-dimensional polyacrylamide gel electrophoresis. In some instances spermatozoa were also surface labelled with tritiated borohydride in the presence of galactose oxidase. Soluble proteins in blood serum, rete testis fluid and cauda epididymal plasma were also iodinated and separated by gel electrophoresis. In addition, aliquants of the radioactive sperm extracts, blood serum and reproductive tract fluids were each immunoprecipitated with polyspecific antisera directed against either testicular sperm membranes, caudal sperm membranes, blood serum, rete testis fluid or cauda epididymal plasma before gel electrophoresis. From the patterns of radioactive proteins detected on the resultant gels, a two-dimensional map was created for each of the sperm extracts and for the various fluids. Proteins which were nonhomologous between testicular and caudal spermatozoa were identified, as well as proteins which were common to spermatozoa and reproductive tract fluids. Epididymal transit was characterized by the loss of certain proteins from the sperm surface, including three borohydride-labelled proteins of M_r 130 000, and by the addition of others, most notably a highly abundant protein of M_r 42 000. Several of the proteins lost from spermatozoa accumulated in the epididymal plasma whilst some of those added to the sperm surface could be identified as direct secretory products of the epididymis. Rete testis fluid contained blood proteins in addition to others presumed to be testis-specific, whilst the composition of cauda epididymal plasma was markedly different from blood serum or rete testis fluid. Proteins that occurred in reproductivetract fluids and also on spermatozoa, but did not show a marked change in abundance on spermatozoa during epididymal transit, included transferrin, albumin and two closely related proteins of M_r 22 000.