Expression and cellular localization of contraception-associated protein 1

Treatment of male rats with ornidazole results in reversible infertility, w hich is associated with the detection of the contraception-associated prote in 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 be en classified as a novel oncogene. Reverse transcription of total ribonucle ic acid (RNA) from various species indicated that a gene similar to CAP1 wa s also expressed in the testes of hamsters, mice, cynomolgus monkeys, and h umans. Detection of RNA expression in rats at the cellular level by in situ hybridization revealed a stage-specific CAP1 expression in the cytoplasm o f pachytene spermatocytes (stages IX-XIII), secondary spermatocytes (stage XIV), and round spermatids (stages I-VII). Immunolocalization of CAP1 in ra t 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 exhibite d on the equatorial segment of the sperm head and cytoplasmic droplets. Flo w cytometric analysis of sperm from omidazole-fed rats revealed a significa nt decline (of 22%-24%) in the amount of sperm surface CAP1 compared with c ontrols, which is associated with an altered location on the sperm head. Th ese observations support a putative role of the protein in the fertilizatio n process.