'Genetic switch' determines whether germ cells become sperm or eggs

Scientists have found a gene switch that controls whether germ cells eventually become sperm or eggs.

New experiments in the Japanese rice fish show that the fox13 gene appears to be the switch that determines whether a germ cell becomes an egg or sperm cell.

The finding could help researchers learn more about how the sexual fate of germ cells is determined during vertebrate development.

Toshiya Nishimura and colleagues demonstrated that fox13, which is expressed in germ cells but not in the surrounding cells of the fish's reproductive organs, provides a molecular cue that prevents the start of sperm formation.

When the researchers disrupted fox13 in adult fish with two X chromosomes (the female state), sperm formed in the female ovary. These sperm were functional and could fertilize eggs normally.

The results indicated that germ cells in these fish, and potentially other vertebrates, do not need to be in the environment of the male reproductive organ to begin their switch into sperm.