A novel role for ribonuclease 9 in suppressing sperm capacitation and acrosome reaction

Ribonuclease 9 (RNase 9) is a member of the ribonuclease A superfamily, which is mainly expressed in the epididymis. However, it has no ribonucleolytic activity and its function remains unclear. Immunofluorescence experiments showed that the localization of RNase 9 protein on the sperm surface has moved from the neck to the acrosome cap during capacitation and acrosome reaction. Chlortetracycline staining was used to assay the role of RNase 9 on capacitation and acrosome reaction. The spontaneous acrosome reaction induced by progesterone could be suppressed by RNase 9 protein and the acrosome reaction ratio was 6.5 +/- 1.2%. Furthermore, exposure of spermatozoa to RNase 9 protein reduced the level of cyclic AMP significantly during the acrosome reaction. Taken together, we confirmed that RNase 9 protein could impair sperm function, including capacitation and acrosome reaction, and had potential role in male reproductive toxicity.