25 April 2000
by George Atkinson
The discovery of a distinct family of proteins (known as the L2 family) which bind to human sperm may offer significant insights into male fertility and possibly even male contraception.
The new proteins are secreted in the epididymis, a coiled tubular network several yards long attached to the top of each testicle. During maturation sperm pass through the epididymis into the vas deferens (and are then emptied via the urethra during ejaculation). Apparently the epididymis has traditionally been overlooked as it was considered by doctors as essential for the development of sperm's fertilizing ability. According to Susan Hall, PhD, of scientists at University of North Carolina Chapel Hill School of Medicine, "Now it's known that sperm that have not passed through the epididymis fertilize an egg very poorly if at all. And after they pass through, they're more ready to fertilize an egg. In the epididymis, sperm go through certain maturational steps that are not very well understood at this point.
That's why we're studying proteins that are synthesized in the epididymis and secreted into that tubule that might possibly interact with sperm in such a way to affect their maturation."
Hall's team were driven to attempt to fill in the gaps in molecular biology of the epididymis as a way to find possible protein targets for male contraception. What they found were three categories of HE2 epididymal proteins -- alpha, beta, and gamma, all of which were regulated by the male hormone testosterone.
The H2 proteins are androgen-regulated, epididymis-specific proteins are unique because they have no known homologues. This may indicate that their function is unique, and "which is why we feel it's another hint that they're involved in fertility," Hall said.
After this initial discovery Hall's team will now undertake further research aimed at discovering exactly what these epididymis-specific proteins do. If they can work this out they can probably identify one or more targets for a male contraceptive.