Expression and cellular localization of contraception-associated protein.

Treatment of male rats with ornidazole results in reversible infertility, which is associated with the detection of the contraception-associated protein 1 (CAP1) in epididymal fluid. The protein, which is present in sperm but not detectable in epididymal fluid of fertile rats, seems to be shed from sperm during ornidazole administration. Cloning and characterization of the gene revealed a high degree of similarity between CAP1 and DJ-1 (Wagenfeld et al, 1998b) a protein that was recently found in humans and which has been classified as a novel oncogene. Reverse transcription of total ribonucleic acid (RNA) from various species indicated that a gene similar to CAP1 was also expressed in the testes of hamsters, mice, cynomolgus monkeys, and humans. Detection of RNA expression in rats at the cellular level by in situ hybridization revealed a stage-specific CAP1 expression in the cytoplasm of pachytene spermatocytes (stages IX-XIII), secondary spermatocytes (stage XIV), and round spermatids (stages I-VII). Immunolocalization of CAP1 in rat testis showed a strong staining of elongating spermatids (stages VI-VIII), indicating a translational delay of CAP1 expression. The location of CAP1 on sperm depended on the method of fixation used, with CAP1 being exhibited on the equatorial segment of the sperm head and cytoplasmic droplets. Flow cytometric analysis of sperm from ornidazole-fed rats revealed a significant decline (of 22%-24%) in the amount of sperm surface CAP1 compared with controls, which is associated with an altered location on the sperm head. These observations support a putative role of the protein in the fertilization process.