Genomic structure and tissue-specific expression of human and mouse genes encoding homologues of the major bovine seminal plasma proteins.

Sperm capacitation is a maturation event that takes place in the female reproductive tract and is essential for fertilization. A family of phospholipid-binding proteins present in bovine seminal plasma (BSP proteins) binds the sperm membrane at ejaculation and promotes bovine sperm capacitation. Homologues of these proteins have also been isolated from boar, ram, goat, bison and stallion seminal fluid, suggesting that BSP proteins and their homologues are conserved among mammals. However, there have been no reports on BSP-homologous proteins in mice and humans to date. A search of the mouse and human genomes, using the nucleic acid sequences of BSP proteins, revealed the presence of three BSP-like sequences in the mouse genome, named mouse BSP Homologue 1 (mBSPH1), mBSPH2 and mBSPH3, and one sequence in the human genome (hBSPH1). Mouse epididymal expressed sequence tags corresponding to partial sequences of mBSPH1 and mBSPH2 were identified. The entire complementary DNA (cDNA) sequences of mBSPH1 and mBSPH2 from mouse epididymis and hBSPH1 from human epididymis were obtained by 5'-/3'-rapid amplification of cDNA ends (RACE) and encode predicted proteins containing two tandemly repeated fibronectin type II domains, which is the signature of the BSP family of proteins. Using RT-PCR, it was revealed that mBSPH1, mBSPH2 and hBSPH1 mRNA are expressed only in the epididymis. Expression of mBSPH3 was not detected in any tissue and probably represents a pseudogene. This work shows, for the first time, that BSP homologues are expressed in mouse and human and may be involved in sperm capacitation in these species.