Two Rat Middle-Piece Coating Antigens Are Lost upon in vitro Capacitation

Abstract

The rat sperm-binding antigen, CFS, contains two subunits, RSV IV and RSV V. Sperm-bound RSV IV was previously detected using anti-RSV IV antibodies, while the presence of RSV V on the cell surface was doubtful. The RSV V subunit was purified from rat seminal vesicle secretion by gel filtration and ionic exchange chromatography. Rabbit polyclonal mono-specific antibodies against either RSV IV or RSV V were used to monitor the binding of the CFS complex onto the rat spermatozoa in indirect immunofluorescence experiments with FITC-conjugated goat anti-rabbit antibodies. Caudal epididymal spermatozoa were incubated in vitro with CFS and evidence of the presence of both subunits on the cell surface was obtained as the heterodimeric sperm-coating antigen was detected on the whole tail. Restriction of the CFS binding sites to the middle-piece surface domain of ejaculated spermatozoa was observed. In addition, release of CFS from this plasma membrane region was observed after in vitro capacitation. The localization of CFS before capacitation and its absence from the sperm surface after capacitation are compatible with a role of this factor as an inhibitor of motility in rat decapacitation.

Localisation and capacitation-dependent loss of buffalo sperm-coating antigens shared with rat sperm

“…Binding of the rat CFS antigen to the tail region of buffalo epididymal spermatozoa and the identification of buffalo CFS-like antigens on the same region of ejaculated spermatozoa suggest that the sperm-protein interaction has been mantained, during evolution, in the two species. As already mentioned, the CFS antigen was suggested to inhibit motility of rat sperm (Bergamo et al, 1993). In fact, addition of a protein fraction containing the CFS subunits decreased the motility of rat epididymal spermatozoa (Pietz & Mabee, 1990).…”

“…The rat seminal vesicle secretory protein CFS, so called because it is a Complex constituted by the subunits RSV IV and RSV V (also known as proteins F and S, respectively) (Manco et al, 1989), was found capable of binding in vitro to epididymal spermatozoa and was extracted from ejaculated spermatozoa . This sperm-coating antigen was localised on the tail of decapacitated cells and was lost upon capacitation (Bergamo et al, 1993). In rat, previous data on sperm motility inhibition by a CFS-containing protein fraction from seminal vesicle fluid (Peitz & Mabee, 1990) suggest that CFS might play a role in regulating flagellar movement.…”

“…The CFS protein was previously shown to be capable of binding in vitro to rat cauda epididymal spermatozoa (Bergamo et al, 1993). The rat sperm-coating antigen might bind in vitro also to buffalo spermatozoa.…”