Transcriptomic Response of the Ovarian Follicle Complex in Post-Vitellogenic Rainbow Trout to 17α,20β-Dihdroxy-4-pregnen-3-one In Vitro

Gonadotropins and progestins are the primary regulators of follicle maturation and ovulation in fish, and they require complex communication among the oocyte and somatic cells of the follicle. The major progestin and the maturation-inducing hormone in salmonids is 17α,20β-dihdroxy-4-pregnen-3-one (17,20βP), and traditional nuclear receptors and membrane steroid receptors for the progestin have been identified within the follicle. Herein, RNA-seq was used to conduct a comprehensive survey of changes in gene expression throughout the intact follicle in response to in vitro treatment with these hormones to provide a foundation for understanding the coordination of their actions in regulating follicle maturation and preparation for ovulation. A total of 5292 differentially expressed genes were identified from our transcriptome sequencing datasets comparing four treatments: fresh tissue; untreated control; 17,20βP-treated; and salmon pituitary homogenate-treated follicles. Extensive overlap in affected genes suggests many gonadotropin actions leading to the acquisition of maturational and ovulatory competence are mediated in part by gonadotropin induction of 17,20βP synthesis. KEGG analysis identified signaling pathways, including MAPK, TGFβ, FoxO, and Wnt signaling pathways, among the most significantly enriched pathways altered by 17,20βP treatment, suggesting pervasive influences of 17,20βP on actions of other endocrine and paracrine factors in the follicle complex.