Brain Transcriptome Analysis Reveals Metabolic Changes Adapting to Hyperhaline or Hypohaline Environments in Spotted Scat(Scatophagus argus)

The fish brain is crucial for adjusting to environmental changes.Metabolic changes play a vital role in the adaptation to salinity change in aquatic animals.However,few studies have evaluated the responses of the fish brain to salinity changes.To evaluate the response to various salinities,spotted scat(Scatophagus argus)was cultured in water with salinity levels of 5(low salinity:LS),25(control group:Ctrl),and 35(high salinity group:HS)for 22 days.The brain transcriptome was analyzed.In total,1698 differentially expressed genes(DEGs)were identified between the HS and Ctrl groups,and 841 DEGs were identified between the LS and Ctrl groups.KEGG analysis showed that the DEGs in the HS vs.Ctrl comparison were involved in steroid biosynthesis,terpenoid backbone biosynthesis,fatty acid biosynthesis,ascorbate and aldarate metabolism,other types of O-glycan biosynthesis,and fatty acid metabolism.Glyoxylate and dicarboxylate metabolism,one carbon pool by folate,steroid biosynthesis,and cysteine and methionine metabolism were significantly enriched in the LS vs.Ctrl comparison.Additionally,the genes related to metabolism(acc,fas,hmgcr,hmgcs1,mvd,soat1,nsdhl,sqle,cel,fdft1,dnmt3a and mtr)were significantly up-regulated in the HS vs.Ctrl comparison.The genes related to metabolism(lipa,sqle,acc,fas,bhmt,mpst,dnmt3a,mtr,hao2,LOC111225351 and hmgcs1)were significantly up-regulated,while hmgcr and soat1 were significantly down-regulated in the LS vs.Ctrl compparison.These results suggest that salinity stress affects signaling pathways and genes’expressions involved in metabolic processes in the brain,and the differences in metabolism play an important role in adaptation to hyperhaline or hypohaline environments in spotted scat.This research provides a comprehensive overview of transcriptional changes in the brain under hyperhaline or hypohaline conditions,which is helpful to understand the mechanisms underlying salinity adaptation in euryhaline fishes.

Sequencing, de novo assembly and characterization of the spotted scat Scatophagus argus(Linnaeus 1766) transcriptome for discovery of reproduction related genes and SSRs

Spotted scat( Scatophagus argus) is an economically important farmed fish, particularly in East and Southeast Asia. Because there has been little research on reproductive development and regulation in this species, the lack of a mature artificial reproduction technology remains a barrier for the sustainable development of the aquaculture industry. More genetic and genomic background knowledge is urgently needed for an in-depth understanding of the molecular mechanism of reproductive process and identification of functional genes related to sexual differentiation, gonad maturation and gametogenesis. For these reasons, we performed transcriptomic analysis on spotted scat using a multiple tissue sample mixing strategy. The Illumina RNA sequencing generated 118 510 486 raw reads. After trimming, de novo assembly was performed and yielded 99 888 unigenes with an average length of 905.75 bp. A total of 45 015 unigenes were successfully annotated to the Nr, Swiss-Prot, KOG and KEGG databases. Additionally, 23 783 and 27 183 annotated unigenes were assigned to 56 Gene Ontology(GO) functional groups and 228 KEGG pathways, respectively. Subsequently, 2 474 transcripts associated with reproduction were selected using GO term and KEGG pathway assignments, and a number of reproduction-related genes involved in sex differentiation, gonad development and gametogenesis were identified. Furthermore, 22 279 simple sequence repeat(SSR) loci were discovered and characterized. The comprehensive transcript dataset described here greatly increases the genetic information available for spotted scat and contributes valuable sequence resources for functional gene mining and analysis. Candidate transcripts involved in reproduction would make good starting points for future studies on reproductive mechanisms, and the putative sex differentiation-related genes will be helpful for sex-determining gene identification and sex-specific marker isolation. Lastly, the SSRs can serve as marker resources for future research into genetics, marker-assisted selection(MAS) and conservation biology.