Transcriptomic analysis of gill tissues in blunt snout bream (Megalobrama amblycephala) under hypoxia and bacterial infection.

Abstract

Blunt snout bream (Megalobrama amblycephala) is an important commercial freshwater fish species in China's aquaculture system. It is unknown how the interaction of bacterial infections and dissolved oxygen concentration affects the gene expression and physiological function of the gill tissues in this fish species. Therefore, fish were exposed to hypoxic conditions and challenged with Aeromonas hydrophila. Then, fish were classified into resistant (H-RMA) and sensitive (H-SMA) groups based on their survival outcomes. Gill tissues were collected for RNA-Seq and functional analysis. A total of 36,774 expressed genes, encompassing 33,852 known genes and 2922 novel genes were identified and around 93&#xa0;% of these genes were correctly mapped to the reference genome. A comparative expression analysis between H-RMA and H-SMA fish revealed 5482 differentially expressed genes (DEGs) encompassing 2557 up-regulated and 2925 down-regulated genes. The examination of KEGG pathways revealed significant enrichment in DNA replication, proteasome, cell cycle, mismatch repair, oxidative phosphorylation and cellular senescence. Obviously structural alterations were observed in the gill tissues, resulting from the compounded impact of hypoxic stress and bacterial infection. Moreover, antioxidant enzymes (SOD, CAT) and immune enzyme activity modulation (ACP and AKP) were significantly (p&#xa0;<&#xa0;0.05) changed between H-RMA and H-SMA groups. Our findings suggest a strong connection between cell cycle arrest and cellular senescence, indicating that resistance to these environmental stresses may depend on the capacity of the cellular senescence pathway to coordinate an immune response localized in the gills.