Early development of the ovary

Published on February 24, 2021   38 min

Other Talks in the Series: The Female Reproductive System: from Basic Science to Fertility Treatments

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Good morning, I'm Blanche Capel, I'm in the Department of Cell Biology at Duke University Medical Center. I'm going to talk to you today about the early development of the ovary.
I'd like to start with the basic information about how the testis and ovary form in the embryo. Sex determination (that is the decision to form a testis or an ovary) depends in mammals, on whether or not you inherit a Y chromosome from your father. As you all know, females contribute only an X-bearing oocyte, but the father can contribute an X- or Y-bearing sperm. Depending on which fertilizes the oocyte, the genetic sex of the embryo will be XX or XY. While this is determined at fertilization, the phenotypic sex of the embryo is not determined until about mid-gestation in the mouse and about six to seven weeks in humans, when the fate of the gonad is determined. Typically, the gonad develops as a testis if there is a Y chromosome present, so in embryos that are XY or even those that are XXY or XYY (unusual combinations) the gonad will develop as a testis. However, if an embryo is XX, XXX or even XO, the gonad will develop as an ovary.
Because the testis and ovary arise from the same primordial early gonad, the gonad is a very valuable model of fate commitment. One of the questions that has occupied the field for some time is: how do the bipotential cells in the early gonad resolve their fate and commit to a developmental pathway? This occurs between E10.5 and E12.5 in the mouse, and as I said, between six and seven weeks in humans. The testis and ovary both arise from the same bipotential primordial gonad. If you have a Y chromosome and the SRY gene on the Y chromosome is present, then typically the gonad forms a testis barring other complications. But if you do not have a Y chromosome then the testis forms an ovary.