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Identification of Germline Stem Cells in the Ovary of the Teleost Medaka

Science  18 Jun 2010:
Vol. 328, Issue 5985, pp. 1561-1563
DOI: 10.1126/science.1185473

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Keeping Egg Production Going

Whether oogenesis ceases around birth in vertebrate ovaries has been a topic of long-standing interest and considerable debate. Nakamura et al. (p. 1561, published online 20 May) now identify germline stem cells in the ovary of the teleost fish medaka. The stem cells are found as clusters of germ cells (termed germinal cradles) in a cord-like structure that expresses sox9, a gene critical for testis formation in mammals. The cords are buried within the ovary within the germinal epithelium. This work in fish shows that there can indeed be continuing egg production from vertebrate germline stem cells.

Abstract

Germline stem cells continually produce sperm in vertebrate testes, whereas there is no direct evidence showing that germline stem cells are present in adult vertebrate ovaries. By using transgenic methods and clonal analysis, we identified germline stem cells that supported oogenesis and the production of offspring in the ovaries of adult medaka fish. Early-stage germ cells were localized in clusters along interwoven threadlike cords of sox9b-expressing somatic cells (termed germinal cradles) where the germ cells developed. Germline stem cells gave rise to germ cells that divided to produce cysts, which then underwent cell death or separated to form follicles. Our results provide insight into the germline stem cell biology of medaka and provide a model system for studying vertebrate stem cell niches.

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