The sperm that initially emerge from the mammalian testis cannot swim or fertilize an egg. Passage through a specialized organ - termed the epididymis - is required to complete the maturation process, but exactly how this occurs remains unclear. Now research in the May issue of Nature Cell Biology from Chang Chan and colleagues shows that a protein important for defence against pathogens may also be required for sperm maturation, suggesting a possible common basis for some sexually transmitted diseases (STDs) and infertility.
b-defensins are short proteins known for their protective action against microbes. The researchers now show that a rat b-defensin, Bin1b, binds to sperm and is critical for normal sperm maturation in rats. In the absence of Bin1b, the movement of sperm from the epididymis is severely impaired.
This work demonstrates that the function of defensin molecules is probably not restricted to host defence, but might also be required for sperm maturation. As these defensins are also present in the epididymis of humans, they might present a potential new therapeutic target in the treatment of both STDs and infertility.
Hsiao Chang Chan (The Chinese University of Hong Kong, China)
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