Identification, evolutionary analysis and functional analysis of the SLC12 gene family in Gymnocypris przewalskii for saline-alkali adaptation

Gymnocypris przewalskii is capable of surviving in both freshwater and brackish water, and exhibits robust osmotic pressure adaptation and regulatory mechanisms. The solute carrier family 12 (SLC12) represents a crucial group of plasma membrane-bound transporter proteins responsible for the coordinated movement of Na⁺, K⁺, and Cl⁻ ions. These evolutionarily conserved proteins play fundamental roles in maintaining cellular homeostasis, including cell volume regulation, blood pressure control, and ion balance maintenance. This study aimed to investigate the evolutionary mechanisms and functional contributions of the SLC12 gene family in the adaptation of G. przewalskii to saline-alkaline environments. Employing an integrated bioinformatics approach, this study systematically identified and characterized SLC12 family members across three teleost species: G. przewalskii, Cyprinus carpio, and Oncorhynchus mykiss. Comprehensive phylogenetic reconstruction and structural analyses were performed, followed by tissue-specific expression profiling of 11 distinct tissues in G. przewalskii using quantitative real-time PCR (RT-qPCR), with particular emphasis on gill and kidney responses to salt and saline-alkaline stress conditions. The study identified a total of 51 complete SLC12 genes in G. przewalskii, divided into ten subtypes (SLC12A1-SLC12A10) , consistent with those subtypes in the C. carpio. However, the O. mykiss genome lacks the SLC12A10 subfamily. Structural domain analysis revealed the characteristic presence of amino acid permease or potassium-chloride cotransporter domains across family members. Tissue-specific expression profiling demonstrated elevated expression of SLC12A2, SLC12A7, and SLC12A10 in gill and kidney tissues, while SLC12A1, SLC12A3, and SLC12A9 showed kidney-enriched expression. Upon salinity and saline-alkaline stress, the expression of SLC12A1, SLC12A3 and SLC12A10 exhibited a downward trend in the kidney, however, the expression levels of SLC12A1, SLC12A2, and SLC12A3 showed a significant increasing trend in the gill. This study demonstrates that the SLC12 family exhibits significant differences in expression levels across different tissues of G. przewalskii and play differential osmoregulatory roles during adaptation to saline-alkaline environments. It represents the first systematic identification and expression characterization of the SLC12 gene family in this species, providing potential molecular targets for research on adaptive evolution of fish to extreme environments and for biological resource conservation in saline-alkaline waters.