Identification of RS as a flagellar and head sperm protein

RS is 20-kDa microtubule-associated protein found in several human tissues. Sequence analysis showed that the polypeptide is highly related to a rat p rotein whose level has been previously reported to be correlated with sperm fertility. The present study examines the intracellular distribution of RS in spermatozoa from both humans and rats employing a specific antibody to the polypeptide and immunofluorescence microscopy. We demonstrate that in h umans, RS is mainly a flagellum protein, but in rats, it is also abundant i n the sperm head. In the sperm tail, RS was found to be co-localized with b eta-tubulin, a major component of the axoneme, suggesting that RS is also a ssociated with the flagellum axoneme. Contrary to a previous report, incuba tion of isolated spermatozoa from both humans and rats in the presence of o rnidazole, a reported male contraceptive drug in rats, did not result in mo dulation in the level of RS, suggesting that the drug does not act directly on sperm RS. (C) 2000 Wiley-Liss, Inc.