Fibroblast Growth Factor May Regulate the Initiation of Oocyte Growth in the Developing Ovary of the Medaka, Oryzias latipes

The distribution of fibroblast growth factor (FGF) was investigated in developing and matured ovaries of the medaka, Oryzias latipes. In the fry, FGF localized in the cytoplasmic region of all oocytes in the ovary at the pre-vitellogenic stage. Before the initiation of vitellogenesis, it disappeared in the cytoplasmic region and newly appeared around each oocyte, and then it localized around all oocytes in the ovary at the vitellogenic stage. Interestingly, the change in FGF distribution was orderly occurring from the posterior to anterior region of the ovary. In the adult, FGF was detected by immunofluorescence staining around the oocytes. These results suggest that FGF plays a significant role in the initiation of oocyte development through follicle cells, and the expression of FGF is rigidly regulated in the developing ovary of O. latipes.