Sudipta Maitra
Visva-Bharati University, India
Title: Expression of insulin receptor subtypes, insra and insrb, in the Zebrafish, Danio rerio ovary and insulin regulation of ovarian function
Biography
Biography: Sudipta Maitra
Abstract
In addition to pituitary gonadotropins and gonadal steroids, insulin and insulin-like growth factors (IGFs) are considered as important regulator of ovarian function. The present study aims at detection of cognate insulin receptors (IRs) and seeks to explore physiological significance of insulin action in the zebrafish ovary. Transcripts for insra and insrb were detected in liver, intact ovarian follicles and denuded oocytes through reverse transcriptase (RT)-PCR. Anti-IRβ immunoreactivity was detected in the ovary through fluorescence microscopy and immunoblot analysis using IRβ specific antibody could detect a single 95 kDa band in the membrane preparation from intact follicles and denuded oocytes harvested from adult zebrafish. In addition to its positive influence on follicular steroidogenesis, stimulation with recombinant human (rh)-insulin could trigger meiotic G2-M1 transition in a manner sensitive to translational activation in zebrafish defolliculated oocytes. Priming with insulin promotes resumption of meiotic maturation in PI3K/Akt-dependent manner and oocyte specific phosphodiesterase 3 (PDE3) has been implicated as a possible downstream target. Forced elevation of intra-oocyte cAMP attenuates rh-insulin action on germinal vesicle breakdown (GVBD), MAPK3/1 (ERK1/2) phosphorylation and p34cdc2 kinase activation. Conversely, PKA inhibition by H89/PKI-(6-22)-amide could successfully overcome negative regulation by cAMP and induces GVBD and MAPK activation. Interestingly, elevated phosphorylation of Akt and ERK1/2 concomitant with higher GVBD percentage was noticed in zebrafish oocytes in vivo prior to ovulation. Further, ovarian follicles harvested from streptozotocin (Stz)-injected (i.p.) gravid zebrafish showed poor oocyte quality and compromised ovarian function including steroidogenesis and maturational potential, indicating functional relevance of insulin action on female reproduction.