Ontogeny and Stress-Induced Plasticity of Osmoregulatory Machinery in Exopalaemon carinicauda: Distinct Spatiotemporal Localization of Na+/K+-ATPase and Carbonic Anhydrase Isoforms.

The euryhaline shrimp Exopalaemon carinicauda is a valuable model for studying osmoregulation, yet the developmental establishment and spatial localization of its key ion-transport sites remain unclear. This study investigated the spatiotemporal expression of Na+/K+-ATPase (EcNKA), cytoplasmic carbonic anhydrase (EcCAc), and glycosylphosphatidylinositol-linked carbonic anhydrase (EcCAg) during early ontogeny and their subcellular responses to salinity and alkalinity stress in juvenile gills of E. carinicauda. Quantitative real-time PCR was used to detect the changes in mRNA expression of the three genes at different developmental stages, and immunohistochemistry was employed to determine the spatial localization of the corresponding three proteins. EcNKA and EcCAg mRNA expression peaked at zoea I, while EcCAc peaked at zoea III-IV. Immunostaining demonstrated a wide distribution of the three proteins across multiple tissues in early larvae, with a later restriction primarily to the gill and intestine. In gills, the EcNKA protein localized to septal cells, whereas EcCAc and EcCAg were located in pillar cells with distinct membrane polarities. Under low-salinity and high-alkalinity stress, transcriptional changes and protein-level responses of EcCAc and EcCAg were discordant. In addition, the protein location of EcCAc exhibited a translocation from the apical to the basolateral membrane, while EcCAg showed apical concentration under stress. These findings provide new insights into the ontogenetic establishment and subcellular plasticity of key ion-transport sites in E. carinicauda and help us to understand how euryhaline shrimp integrate developmental programming and saline-alkaline stress responses at both the mRNA and protein levels.