Comparative transcriptome analysis of ovary and testis reveals potential sex-related genes and pathways in spotted knifejaw Oplegnathus punctatus

The spotted knifejaw (Oplegnathus punctatus) is a newly emerging fishery species inhabiting the Pacific Ocean around Hawaii, China, Japan and Korean Peninsula. Little information on the mechanism of gonadal development and gametogenesis in this species could be used for research and breeding work. In this study, RNA-seq technology was applied to generate a deep-coverage sequencing data of spotted knifejaw testis and ovary. A total of 262,392,754 reads (ovary 133,403,270, testis 128,989,484) were generated from the cDNA library. After filtering and assembling, a total of 113,794 unigenes were obtained with the N50 of 1658 bp. Unigenes were annotated with multiple public databases, including non-redundant protein databases (NR) (42,460, 37.31%), Swiss-Prot (33,632, 29.56%), eukaryotic Orthologus Groups (KOG) (26,195, 23.02%), Kyoto Encyclopedia of Genes and Genomes (KEGG) (10,978, 9.65%), and Gene Ontology (GO) (30,514, 26.82%). By comparing ovary and testis, 4496 differentially expressed unigenes (1986 in female, 2510 in male) were identified, in which 469 were specially expressed in females and 859 in males. The expression levels of 12 unigenes were confirmed by qRT-PCR. In addition, 35,054 simple sequence repeats were identified. By GO and KEGG analyses, a set of unigenes related to gonadal development and gametogenesis were filtered. foxl2 was deduced to be a key regulator for gonadal development and gametogenesis in females and dmrt1 in males. bmp15, nanos3, sox9 and amh were likely to function in the regulation of gonad physiology and germ line cells maintenance in ovary and testis. Interestingly, p53, apoptosis, Jak-STAT and neuroactive ligand-receptor interaction pathways were found to be pivotal in regulating gonadal development and gametogenesis of spotted knifejaw in various aspects. This study provides a fundamental support for further research in reproduction biology, population genetics and functional genomics in spotted knifejaw.