Transcriptome analysis of gills reveals novel insights into the molecular response of stinging catfish (Heteropneustes fossilis) to environmental hypertonicity

Abstract

The stinging catfish Heteropneustes fossilis is a champion survivor under hypertonic stress and is suggested to be a profitable candidate for culture in slightly saline water in coastal regions. Fish gills are an essential site of osmoregulation and other physiological processes. To investigate the stress responses and mechanisms of salinity tolerance in stinging catfish, we sampled gills tissues from control and hypertonicity (100 mM NaCl solution) treated adult catfish and assessed for transcriptomic profiling by high throughput sequencing. The raw data generated was filtered and assembled for de novo transcriptome assembly. The final contig assembly produced a total of 1,71,478 unigene transcripts with an average transcript length of 898 bp and a GC content of 45%. A total of 22,231 transcripts matched with Chordata with BLAST search and were functionally annotated, out of which 21,814 were best-hit transcripts aligned with the UniProt database. Comparative transcriptomic analysis revealed that a total of 1951 genes were differentially expressed in the gills of NaCl-treated fish compared to the control. Functional and enrichment analysis of the Differentially expressed genes demonstrated that several GO pathway terms were significantly over-represented, such as 'catalytic activity', 'hydrolase activity' in molecular function category, 'membrane', 'integral component of membrane' in cellular component category and 'metabolic process', 'regulation of transcription' in biological process category. The functional analysis study of DEGs demonstrated that tolerance to hypertonic stress by stinging catfish is associated with a few pathways related to stress response, immune response, biosynthesis, metabolism, molecular transport, cytoskeleton remodeling, apoptosis, cell signaling, transcriptional regulation, etc. The present study provides a novel insight into the molecular responses of the air-breathing stinging catfish against salinity stress, which could elucidate the underlying mechanisms of adaptation of this stenohaline species under various environmental constraints.

Keywords: De novo transcriptome assembly; Environmental hypertonicity; Heteropneustes fossilis; Osmoregulation; RNA seq.