Embryos kill off male tissue to become female | Science News

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Embryos kill off male tissue to become female

A study in mice identifies a protein crucial to developing as a girl

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2:17pm, August 17, 2017
female mouse embryo

DOUBLING UP A normal female mouse embryo (left) has only female reproductive tissue, called the Müllerian duct (pink). Removing a protein called COUP-TFII causes a female mouse embryo (right) to develop both the female duct and male tissue called the Wolffian duct (blue).

Add a new ingredient to the sugar, spice and everything nice needed to make girls.

A protein called COUP-TFII is necessary to eliminate male reproductive tissue from female mouse embryos, researchers report in the Aug. 18 Science. For decades, females have been considered the “default” sex in mammals. The new research overturns that idea, showing that making female reproductive organs is an active process that involves dismantling a primitive male tissue called the Wolffian duct.

In males, the Wolffian duct develops into the parts needed to ejaculate sperm, including the epididymis, vas deferens and seminal vesicles. In females, a similar embryonic tissue called the Müllerian duct develops into the fallopian tubes, uterus and vagina. Both duct tissues are present in early embryos.

A study by French endocrinologist Alfred Jost 70 years ago indicated that the testes

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