CDK5/NFAT5-Regulated Transporters Involved in Osmoregulation in Fejervarya cancrivora

SIMPLE SUMMARY: Amphibians mostly live in freshwater. However, crab-eating frogs (Fejervarya cancrivora) can adapt to high saline environments, while the osmoregulatory mechanism was not fully clear. Cyclin-dependent kinase 5 (CDK5), activating the nuclear factor of the activated T cells-5 (NFAT5) pathway, plays an important role in protecting cells from hypertonicity. We investigated the role of CDK5/NFAT5 in crab-eating frogs’ adaptation to saline environments. As a result, we found that the expression of CDK5/NFAT5 and its downregulated genes were higher in crab-eating frogs, which subsequently regulated ion transport to mediate osmotic pressure. The results indicate that CDK5/NFAT5-regulated transporters are involved in osmoregulation in frogs. ABSTRACT: Crab-eating frogs (Fejervarya cancrivora) can live in brackish water with a salinity of up to 18‰, although most amphibians are not able to tolerate such high saline environments. To investigate its potential osmoregulation, we conducted experiments in F. cancrivora and F. multistriata. The results showed that F. cancrivora made use of ions (such as Na(+) and Cl(−)) to increase intracellular concentrations via the Na(+)/K(+)-ATPase (NKA) enzyme. The mRNA expression of aldose reductase (AR) was significantly higher in F. cancrivora (p < 0.05), indicating that more organic osmolytes were produced and transported to maintain cellular homeosis. The mRNA expressions of Aquaporin 1 (AQP1) and AQP3 in kidney were significantly higher in F. cancrivora, while AQP expression in skin was higher in F. multistriata (p < 0.05). The mRNA level in activating the transcription of the nuclear factor of activated T cells-5 (NFAT5) which is one of the target genes of regulating the cellular response to hypertonicity, was higher in F. cancrivora. The protein expression of CDK5, the upstream protein of the NFAT5 pathway, was 2 times higher in F. cancrivora. Therefore, we can conclude that CDK5/NFAT5-regulated transporters might be involved in osmoregulation in F. cancrivora.