Structural and functional characterization of haemoglobin genes in Labeo catla: Insights into hypoxic adaptation and survival

Haemoglobin (HB) protein comprises four subunits: two identical alpha-subunits (HBA) and two identical beta-subunits (HBB), encoded by the HBA and HBB genes. In this investigation, 5 '/3 ' RACE PCR (Rapid Amplification of cDNA Ends) was used to obtain complete coding sequences (CDSs) of both the genes from farmed Labeo catla. The resulting CDSs were 432 base pairs and 447 base pairs for HBA and HBB, respectively, corresponding to 143 and 148 amino acids. Phylogenetic analysis revealed close relationships with other cyprinids, with Labeo rohita being the closest relative. Functional analysis and protein structure prediction were conducted using bioinformatics tools. Expression profiling of both genes was checked in various tissues under control (C) and hypoxic (H) conditions. Notably, under hypoxia, HBA and HBB genes were significantly upregulated (P < 0.05) initially, followed by a return to normal expression levels. Similar trends were observed for Hif1 alpha (Hypoxia-inducible factor one alpha) and EPO (Erythropoietin) genes. Additionally, haematological indices also significantly increased corresponding to the gene expressions. However, with the decrease in the expression of these genes an onset of mortality was observed in the hypoxia (H) treated groups. The results of the current study explored the role of haemoglobin genes in adaptation to the hypoxic condition.