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.