Transcriptome profiling of the hypothalamus and pituitary at gonadal maturation and regression phases in marbled flounder (Pseudopleuronectes yokohamae)

The Pseudopleuronectes yokohamae (marbled flounder) features one of the most commercially important marine fishes in P.R. China. Previous studies were mainly focused on the biology and genetic breeding of the fish, little have been reported about the molecular mechanism of its reproduction. In this study, we used second generation Illumina sequencing to investigate the genes of Pseudopleuronectes yokohamae that regulate gonadal development and obtained 40,882 unigenes from the hypothalamus and pituitary samples of the fish at maturation and regression phases. Homogonous sequences of 29,129 unigenes (71.25 %) were identified and 308 unigenes among which were associated with the regulation of reproductive endocrine. These genes are a very useful resource for future studies of P.yokohamae. All unigenes with eggNog annotations were divided into 26 categories that are mostly involved in signal transduction, translation mechanism, physiological and biochemical processes, etc. Based on KEGG analysis, all unigenes expressed at the maturation phase were involved in 107 metabolic pathways, with 184 up-regulated sequences, while the unigenes expressed at the regression phase were related to 210 metabolic pathways, with 858 up-regulated sequences. Additionally, the quantitative real-time PCR results indicated that follicle stimulating hormone and prolactin-releasing peptide receptor are highly expression at the regression phase, while growth hormone releasing hormone, kisspeptin, gonadotropin and insulin growth-like factors expressed higher at the maturation phase. This study provides valuable data for better understanding the transcriptome profiles of marbled flounder and may help to improve artificial reproduction technologies of the fish.