Analysis of transcriptome profiling from the brain at maturation and regression phases in starry flounder (Platichthys stellatus)

Abstract

This study was to investigate the regulatory mechanisms of reproduction and endocrinology in starry flounder (Platichthys stellatus). Total RNA from the mixed sample of pituitary gland and hypothalamus of brain at the maturation and regression phases was isolated. The RNA sequencing (RNA-Seq) library was prepared and sequenced on Illumina Hiseq 2000 platform. A total of 53,567,296 and 75,630,680 short fragments were obtained from the samples of maturation and regression phases, respectively. After splicing, 30,640 unigene sequences were obtained based on the blasting results from National Center for Biotechnology Information (NCBI) database. Homogonous sequences of 24,128 unigenes (78.8%) were found and analyzed with eggNOG and KEGG (Kyoto Encyclopedia of Genes and Genomes). All 24,128 unigenes with eggNOG annotations were divided into 26 categories that are mostly associated with physiological processes, including signaling transduction, translation mechanism, etc. Based on KEGG analysis, all unigenes at the maturation phase were involved in 98 metabolic pathways, with 135 up-regulated sequences, while the unigenes at the regression phase were related to 192 metabolic pathways, with 648 up-regulated sequences. Moreover, 334 differentially expressed genes (DEGs) were up-regulated at the maturation phase, while 987 up-regulated DEGs were found at the regression phase. Total 408 unigenes were associated with the regulation of reproduction and endocrinology. The mRNA expression of some reproduction-associated DEGs including growth hormone releasing hormone (GnRH), neurokinin B (NKB), gonadotropin (GtH), follicle stimulating hormone (FSH), kisspeptin (Kiss) and prolactin-releasing peptide receptor (PrRPR) in the hypothalamus and pituitary gland at two phases was verified by qRT-PCR. Except FSH, all other 5 DEGs showed higher expression at the regression phase. This study provides valuable data for understanding the transcriptome profiles of starry flounder brain and improving the technologies of artificial breeding.