Transcriptome analysis of ovarian maturation in a chondrostei Chinese sturgeon Acipenser sinensis

Chinese sturgeon (Acipenser sinensis) with an evolutionary history of over 200 million years, has a long lifespan, and an extremely late and asynchronous sexual maturation (8-18 years for males and 14-26 years for females), resulting in the difficulty of mature adult culture. However, little is known about the regulatory mechanisms of the transition among ovarian maturation stages in the Chinese sturgeon. We performed de novo transcriptome sequencing of the Chinese sturgeon at different ovarian maturation stages (FII, FIII, and FIV). The number of differentially expressed genes (DEGs) between FII and FIII/FIV (33,517/34,217) was more than that between FIII and FIV (22,123), suggesting that the transition from FII to FIII/FIV is more important than that from FIII to FIV for ovarian maturation. The number of upregulated genes was more than that of the downregulated genes, suggesting that increased gene expression was involved in the transition from FII to FIII/FIV. The representative pathways of DEGs were steroid biosynthesis, fatty acid biosynthesis, fatty acid elongation, glycerolipid metabolism, biosynthesis of unsaturated fatty acid, and α-linolenic acid metabolism. The differential expressions from the transcriptome sequencing were validated with real-time reverse-transcription polymerase chain reaction. We also found 13 genes in sexual development, female sex determination, gonadal development, ovarian maturation, ovarian follicle development, and oocyte development pathways, which were differently expressed among fish at FII, FIII, and FIV. We suggest that enhanced synthesis of steroid, unsaturated fatty acid, and α-linolenic acid may contribute to ovarian maturation of the Chinese sturgeon. These potential determinants provide a glimpse of the molecular architecture of ovary development in sturgeons.