A small molecule that reversibly lowered sperm count and rendered sperm immobile in male mice has potential as a male contraceptive.

Martin Matzuk at Baylor College of Medicine in Houston, Texas, James Bradner at the Dana-Farber Cancer Institute in Boston, Massachusetts, and their colleagues show that the molecule, JQ1, binds to a protein called BRDT. This protein is found only in the testes, where it is required for sperm generation. Male mice injected with JQ1 continued to mate normally with females, but they showed shrunken testes and decreased sperm count, and sired no offspring. Within four months of the treatment being stopped, the male mice could impregnate females.

The molecule could be part of a new class of contraceptive drugs that specifically target male sex cells, the authors suggest.

Cell 150, 673–684 (2012)