Localization of intrinsic and extrinsic SVS II immunoreactivity in rat spermatozoa.

A glycoprotein, designated SVS II, is secreted in an androgen-dependent manner from lateral prostate and seminal vesicles of the rat. The pI of the protein is 10.5 and it has a molecular mass of 49 kDa. F-actin isolated from skeletal and heart muscle is precipitated at a ratio of 2:1 by SVS II. Using a polyclonal rabbit antibody against SVS II, we found an immunoreaction at the head region of rat spermatozoa removed from the vas deferens. In addition, immunoreactive material was observed in the principal piece of the sperm tail in those spermatozoa. We have studied the distribution of SVS II-immunoreactive material in spermatozoa isolated from seminiferous tubules, proximal (efferent ductules), and distal (caudal epididymal duct) epididymis, both in sexually active and inactive rats and found a differential reactivity pattern. Immunoreactivity observed in the principal piece of the sperm tail develops only immediately before spermiation and does not change during the epididymal transit of the spermatozoa. Immunolabelling seen in the head portion is first observed in spermatozoa from proximal epididymis. Simultaneous with its appearance, rhodamine-labelled phalloidin, indicating the presence of F-actin, no longer binds to that region. While the immunoreaction of the sperm head is attributed to extrinsic SVS II, added to the sperm head in proximal epididymis, the immunoreactivity of the sperm tail seems to result from a cross reactive intrinsic sperm tail protein that achieves its final structure briefly prior to the onset of spermiation.(ABSTRACT TRUNCATED AT 250 WORDS)