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Baby Development – Battle of Sexes: Ovaries Must Suppress Their Inner Male

Posted Jan 06 2010 6:09pm

By Colleen Hurley, RD, Certified Kid’s Nutrition Specialist

Aside from “when are you due?”, “is it a boy or a girl?” is the most common question an expecting mum hears. Regardless of whether or not parents choose to find out the sex of the baby ahead of time, the gender of the baby is determined months before science or technology can confirm for certain. Gender was thought to be determined by the simple combination of sex chromosomes, but a recent study found out that the ovaries may have to suppress their inner male.

battleofthesexesIn most mammals, including humans, gender is determined by sex chromosomes. Females have two X chromosomes while males have one X and one Y chromosome. The development of ovaries and other traits that make a female a female has been presumed by scientists to simply be a matter of default. The Y chromosome possesses a gene called Sry, which would mean the embryo would develop into a male. The lack of Sry thus meant the embryo would become a female.

Scientists from the European Molecular Biology Laboratory (EMBL) in Heidelberg, Germany, discovered that in adult animals, it is actually the male pathway that requires active suppression. In conjunction with the Medical Research Council’s National Institute for Medical Research (NIML) at Mill Hill, UK; the research team found that if a specific non-sex chromosome gene is turned off, cells in the ovaries of adult mice turn into cells typically found in male sex organs.

The study flies in the face of the long-standing notion that the development of female traits is only a matter of default yet provides poignant insight into how sex determination has evolved. Located on an autosome, or a chromosome other than a sex chromosome, the gene Foxl2 was known to play an important role in female determination but its precise role remained a mystery because the gene is present is both sexes.

The teams from EMBL and NIMR were able to determine the underlying mechanism. NIMR had previously identified the testes (male)- promoting gene Sox9 which functioned in the embryo to promote male characteristics yet recent studies found this gene to be active in adults as well. Researchers found, however, Foxl2 is necessary to keep Sox9 turned off throughout life and as found in this study, to keep a female mouse a female.

Although this may seem like a great deal of scientific discussion, in the realm of genetic research this is exciting news as this study will have wide range implications for reproductive medicine on many levels. For one, it may be able to help treat sex differentiation disorders in children as well as understanding of the masculinizing effects of menopause in females.

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