Transcriptome analysis of ovarian maturation in Chinese sturgeon Acipenser sinensis

Chinese sturgeon, Acipenser sinensis, with an evolution history of over 200 millions year, is a Grade I protected animal in China and AppendixII species in CITES. Chinese sturgeon has a long lifespan, and extremely late and asynchronous sexual mature (8-18 years for males and 14-26 years for females), making difficult to culture mature adults. During rearing, the transition from Stage FII to FIII and FIV of female ovary is the key point for gonadal maturation of Chinese sturgeon. However, little is known about regulation mechanism of the transition and ovarian maturation in Chinese sturgeon. We performed de novo transcriptome sequencing of Chinese sturgeon with different mature stages of ovary (FII, FIII and FIV). We found 33,517 genes to be differentially expressed between FII (As-ovary-A) and FIII (As-ovary-B), 34,217 genes between FII (As-ovary-A) and FIV (As-ovary-C), 22,123 genes between FIII (As-ovary-B) and FIV (As-ovary-C). The number of DEGs between A and B/C are more than those between B and C, suggesting that the transition from FII to FIII/FIV is more important than that from FIII to FIV for ovarian maturation of Chinese sturgeon. Among the DEGs between A and B/C, the number of up-regulated genes were more than those of down-regulated genes, suggesting increased gene expressions were contributed to the transition from FII to FIII/FIV. These genes were involved in several pathways, including steroid biosynthesis, fatty acid biosynthesis, fatty acid elongation, glycerolipid metabolism, biosynthesis of unsaturated fatty acid, and a-linolenic acid metabolism. We also found 13 genes in sexual development pathway, female sex determination and reproduction regulation pathway, gonadal development pathway, ovarian maturation pathway, ovarian follicle development pathway and oocytes development pathway, showed different expression among fish at FII, FIII and FIV. We suggested that enhanced synthesis of steroid, fatty acid, glycerolipid, unsaturated fatty acid, and a-linolenic acid might contribute to the ovarian maturation of Chinese sturgeon. These potential determinants provide a glimpse of molecular architecture of ovary development in sturgeons. It will enrich biomarkers to track the mature stage of females in sturgeons, and improve artificial culture and controlled propagation for conservation stocking.