1 Characterization of Inhibin α Subunit (inha) in the Zebrafish – Evidence for a Potential Feedback Loop between the Pituitary and Ovary

Inhibin and activin are closely related disulphide-linked dimmers that belong to the transforming growth factor β (TGF-β) superfamily. Although inhibin has been extensively studied in mammals, the information about its existence and function in 5 lower vertebrates is very scarce. Using zebrafish as the model, the present study demonstrated that the inhibin-specific α subunit (inha) was predominantly expressed in the gonads and no transcript could be detected in other tissues including the pituitary and brain. In the ovary, the expression of inha was restricted to the somatic follicle cells surrounding the oocyte, together with the β subunits (inhbaa and inhbb). 10 This was further supported by the absence of its expression in the ovulated unfertilized eggs. During folliculogenesis, inha expression in the follicles slightly but steadily increased from primary growth (PG) to mid-vitellogenic (MV) stage; however, its expression surged dramatically at full-grown (FG) stage. Interestingly, the expression level of inha decreased significantly in the follicles whose oocytes 15 were undergoing spontaneous maturation or germinal vesicle breakdown (GVBD)