Developmental tracing of oocyte development in gonadal soma-derived factor deficiency medaka (Oryzias latipes) using a transgenic approach

• We established a transgenic fish line which is able to distinguish oocytes from various stages of development with a multi-color fluorescent combination.
• Targeted disruption of gsdf resulted in a severe problem in female folliculogenesis and fertility, whereas the abnormal folliculogenesis was visualized under fluorescent microscope.
• According to a TGF-β domain sharing between gsdf and inhibin, and inhibin severe suppression in gsdf KO ovary, gsdf deficient medaka provides a good model for insights of TGF-β signaling pathway conserved in folliculogenesis from fish to humans.

Gonadal soma-derived factor (gsdf) is reported to be a male initiator in medaka based on loss- and gain- of function via targeted disruption, or transgenic over-expression. However, little is known about how gsdf promotes undifferentiated gonad entry into male pathways or prevents entry into the female pathway. We utilized a visible folliculogenesis system with a reporter cassette of dual-color fluorescence expression to identify difference between oocyte development from wildtype and gsdf deficiency medaka. A red fluorescent protein (RFP) is driven by a major component of the synaptonemal complex (SYCP3) promoter which enables RFP expression solely in oocytes after the onset of meiosis, and a histone 2b-EGFP fused protein (H2BEGFP) under the control of an elongation factor (EF1α) promoter, wildly used as a mitotic reporter of cell cycle. This mitosis-meiosis visible switch revealed that early meiotic oocytes present in gsdf deficiency were more than those in wildtype ovaries, corresponding to the decrease of inhibin expression detected by real-time qPCR analysis, suggesting gsdf is tightly involved in the process of medaka oocyte development at early stage.