An antimicrobial peptide gene found in the male reproductive system of rats

Little is known about the innate defense mechanisms of the male reproductiv e tract. We cloned a 385-base pair complementary DNA and its genomic DNA na med Bin1b that is exclusively expressed in the caput region of the rat epid idymis and that is responsible for sperm maturation, storage, and protectio n. Bin1b exhibits structural characteristics and antimicrobial activity sim ilar to that of cationic antimicrobial peptides, beta -defensins. Bin1b is maximally expressed when the rats are sexually mature and can be up-regulat ed by inflammation. Bin1b appears to be a natural epididymis-specific antim icrobial peptide that plays a role in reproductive tract host defense and m ale fertility.