An investigation of gene expression patterns that contribute to osmoregulation in Macrobrachium australiense: Assessment of adaptive responses to different osmotic niches

Osmoregulation is considered to be the principal mechanisms for survival and adaptation to different environmental salinity conditions. The present study was conducted to assess mRNA expression levels of five osmoregulatory genes in a Palaemonid prawn species, Macrobrachium australiense, exposed to three different salinities (0‰, 5‰ and 10‰) across six time intervals for a period of five days, using an RT-qPCR approach. Relative mRNA expression patterns revealed comparatively higher expression levels of Na+/K+-ATPase (NKA) and Na+/K+/2Cl− Co-transporter (NKCC) genes at raised salinities (5‰ and 10‰). At 0‰ vs 10‰, expression levels of these two genes were significantly higher (p < 0.05) and showed 2-3 fold and 4-6 fold higher (higher in 10‰ than 0‰) expression levels for NKA and NKCC, respectively. Significantly higher expression levels (p < 0.05) were observed at 0‰ for the Na+/H+ exchanger (NHE) and V-type H+-ATPase (VTA) genes over 5‰ and 10‰ throughout the experimental time period. But initially higher expression levels of VTA were observed at 5‰ and 10‰ up to 24 h and then dropped below the levels at 0‰. The water channel regulatory gene, Aquaporin (AQP) showed very high expression levels initially (1 h) that were significantly different among treatments (p < 0.05), expression levels then declined up to the end of the experiment. In general, AQP, NHE and VTA were up-regulated in freshwater while NKA and NKCC were up-regulated under raised salinities. Results of this study indicate that the genes examined here likely play key roles in adaptive responses to variable environmental salinity conditions broadly in aquatic crustaceans.