ScienceShot: Protein Makes Sperm Flee

A compound that causes immature sperm cells to flee the testes early may provide new leads for contraceptives. Scientists pursuing a "male pill" have recently found multiple ways to disrupt sperm production, usually by shutting down genes and proteins unique to the testes. Now, a team led by C. Yan Cheng of the Population Council's Center for Biomedical Research in New York City has identified a new way to stop spermatogenesis: disrupting the blood-testis barrier, a cellular firewall between the testes and blood circulation. When Cheng's team injected a special protein fragment into rat testes, the blood-testis barrier broke down. This caused immature sperm to drift out of the testes early, before they were capable of fertilizing eggs. More importantly, these changes were reversible. The team reported their findings online today in Nature Communications. Any potential male contraceptive would be many years off and would require many more tests. Cheng's team, for instance, has not tested whether rats injected with this protein fragment father fewer offspring. But Cheng says the advantage of this protein over other potential contraceptives is that the body produces it naturally in small amounts, so it's likely to be well tolerated.

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