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

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.