Everyone's Health

Who cares which came first, we all need sperm and eggs

Developmental biology egged on

While the “which-came-first: the-chicken-or-the-egg” question remains unanswered, Australian researchers say they've solved another fundamental conundrum: Why males produce sperm and females eggs.

According to Dr. Josephine Bowles and Peter Koopman of the Institute for Molecular Bioscience at the University of Queensland, it's all a matter of timing.

The cells that eventually turn into either eggs or sperm, called germ cells, are identical in male and female embryos. Whether a germ cell becomes an egg or a sperm depends upon when development (meiosis) actually begins.

In females, meiosis starts before birth and eggs are produced. In males, meiosis begins after birth, resulting in sperm.

Koopman says the trigger appears to be retinoic acid, a derivative of vitamin A. In females, retinoic acid seems to prompt meiosis. Male embryos, however, possess an enzyme that eliminates retinoic acid, thus suppressing meiosis until after birth.

The discovery, say scientists, is more than just textbook science. Knowing what triggers and suppresses meiosis could help researchers improve fertility treatments and eliminate errant retinoid signals that can lead to germ cell tumors.

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