Impacts of Fsh, Igf1, and high temperature on the expression of genes involved in steroidogenesis, cell communication, and apoptosis in isolated coho salmon previtellogenic ovarian follicles

In salmonids, exposure to elevated temperature impairs oogenesis. As such, there is a need to understand the molecular mechanisms that underpin this process, and develop mitigation strategies that maintain or rescue reproductive development in broodstock. In this study, follicle stimulating hormone (Fsh) and/or insulin-like growth factor 1 (Igf1) treatment were assessed for their ability to promote reproductive function at 14 and 22 °C in ovarian follicles from coho salmon in vitro. Maintenance at 22 °C resulted in the downregulation of fsh receptor, 17α-hydroxylase/C17,20-lyase and p450 aromatase a (cyp19a1a), and connexin 34.3 (cx34.3). While combined treatment with Fsh and Igf1 stimulated the expression of cyp19a1a at 14 °C, this treatment was not effective at 22 °C. Upregulation of cx34.3 occurred in response to treatments that contained Igf1 regardless of temperature, and there is evidence to suggest that apoptosis was inhibited to some extent at 22 °C following combined treatment with Fsh and Igf1. This study demonstrates the thermal impairment of key reproductive genes, and highlights the potential for novel hormone treatments to rescue oogenesis in salmonids.