Changes in plasma membrane glycoproteins of rat spermatozoa during maturation in the epididymis.

Abstract

Glycoproteins on the plasma membrane of testicular and cauda epididymidal spermatozoa have been labeled with galactose oxidase/NaB [aH]4 and sodium metaperiodate/ NaB[3H]4, followed by analysis on SDS polyacrylamide gels. The major glycoprotein labeling on testicular spermatozoa has a molecular weight 110,000 whereas on cauda epididymidal spermatozoa >90% of the radio-label is incorporated into proteins of molecular weight 32,000. These 32,000-mol wt proteins are homologous with proteins of similar molecular weight purified from the epididymal secretion and which have been shown previously to be synthesized in the caput epididymidis under hormonal control. Immunofluorescence revealed that the 32,000-mol wt proteins are present on the flagellum of mature but not immature spermatozoa and that they have a patchy distribution suggesting that they are mobile within the plane of the membrane. The membrane-bound 32,000-mol wt proteins possess hydrophobic domains as revealed by charge-shift electrophoresis and they also label with a lipophilic photoaffinity probe suggesting that they are in contact with the lipid bilayer. The evidence indicates that there is a considerable reorganization of the molecular structure of the plasma membrane of spermatozoa during maturation in the epididymis and that some of the changes are brought about by a direct interaction with epididymal secretory proteins.The acquisition of motility and fertilizing capacity by mammalian spermatozoa as they pass through the epididymis is accompanied by a number of distinct, albeit in some cases subtle, changes in their morphology, composition, and metabohc activity (reviewed in references 2 and 42). That the epididymis plays a significant role in regulating sperm maturation is not in doubt, but relatively little is known about the processes mediating or controlling these changes, the sequence in which they take place, and their relative importance to the ultimate ability of the sperm to fertilize an egg. Recently, interest has focussed on maturation changes in the plasma membrane as the initial events during fertilization involve cellular recognition and membrane fusion. The concept that the plasma membrane of mature spermatozoa is a mosaic of heterogeneous protein and lipid domains has arisen from studies on the binding of lectins (31), distribution of antigens (1, 11,15,16,25,28,30,33), surface charge (21,37,50), and the arrangement ofintramembrane particles (12,29,32). However, it is not altogether clear from these studies whether this heterogeneity is already expressed on spermatozoa in the testis or if it arises by modification of the plasma membrane during maturation in the epididymis.As a preliminary step towards investigating the role of the epididymis in regulating sperm maturation we have examined the synthesis and secretion of proteins and glycoproteins in the rat epididymis (8,26). Several androgen-dependent proteins and one testicular fluid-dependent protein were identified and characterized from the luminal secretions. In this c...

Altered molecular dynamics and antioxidant status in the spermatozoa in testosterone-induced oligospermia in mouse

“…Many modifications of the sperm membrane surface such as masking or unmasking surface molecules and/or addition of certain molecules result from interaction between the spermatozoa and surrounding epididymal epithelium (Brown et al, 1983;Eddy et al, 1985). The activity of epididymis is regulated by androgens.…”

Oviduct binding ability of porcine spermatozoa develops in the epididymis and can be advanced by incubation with caudal fluid

“…Considerable reorganization of sperm plasma membrane glycoproteins does occur during maturation in the epididymis, which can be mediated by a direct interaction with epididymal proteins [38,39]. Moreover, incubation of bovine spermatozoa in caudal fluid facilitates acquisition of a low molecular weight protein capable of stimulating calcium uptake, particularly with caput spermatozoa [40].…”

New Insights into the Origin, Structure and Role of CD52: A Major Component of the Mammalian Sperm Glycocalyx

“…Despite the apparent complexity of the sperm glycocalyx, surface carbohydrate labelling experiments on rat spermatozoa by the galactose oxidase/NaB 3 H 4 -labelling technique show a very high selectivity: the only accessible molecule is an approximately 26-kD glycoprotein [Olson and Hamilton, 1978;Brown et al, 1983;Hamilton et al, 1986;Jones, 1989;Eccleston et al, 1994] which thus would form the major component of the outer rat sperm glycocalyx. The molecule is not detectable in the testis but represents the principal surface glycopeptide on cauda epididymidal sperm.…”