This "genetic switch" could explain the big gonad decision

A groundbreaking study could answer fundamental questions about gender and sex determination, and the process by which cells become either eggs or sperm. While males and females may come from the same basic beginnings, it was unclear until now how the reproductive precursor cells in vertebrates went on to become either the sperm in males or the eggs in females. Turns out, new research from Japan indicates, it's all down to a gene that's particularly active in female animals.

The team at the National Institute for Basic Biology in Aichi, Japan, looked at vertebrate germ cells in small fish called medaka. In particular, the group examined the impact of a gene known as foxl3, and how it shaped sperm–egg fate decision.

Previously, germ cells had been thought to be passive, effected only by the mechanisms of surrounding cells. However, the NIBB researchers discovered, in fact they are uniquely effected by foxl3: without it, the germ cells invariably change into sperm.

To test the findings, the scientists inactivated the gene in samples of female medaka fish. When that was the case, the germ cells developed into sperm within the ovaries, where you'd commonly expect to find eggs.

Somewhat astonishingly, those sperm – despite being produced by a female fish – were found to be fully able to fertilize an egg from another fish, and indeed produce healthy baby fish.

As the NIBB team makes clear, foxl3 is not a gene that's found in the human reproductive system. However, it's suggested that a similar genetic switching is responsible for the mechanism that controls egg or sperm creation in human females and males.

SOURCE National Institute for Basic Biology

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