Molecular and functional characterization of seven Na+/K+-ATPase β subunit paralogs in Senegalese sole (Solea senegalensis Kaup, 1858).

In the present work, seven genes encoding Na(+),K(+)-ATPase (NKA) β-subunits in the teleost Solea senegalensis are described for the first time. Sequence analysis of the predicted polypeptides revealed a high degree of conservation with those of other vertebrate species and maintenance of important motifs involved in structure and function. Phylogenetic analysis clustered the seven genes into four main clades: β1 (atp1b1a and atp1b1b), β2 (atp1b2a and atp1b2b), β3 (atp1b3a and atp1b3b) and β4 (atp1b4). In juveniles, all paralogous transcripts were detected in the nine tissues examined albeit with different expression patterns. The most ubiquitous expressed gene was atp1b1a whereas atp1b1b was mainly detected in osmoregulatory organs (gill, kidney and intestine), and atp1b2a, atp1b2b, atp1b3a, atp1b3b and atp1b4 in brain. An expression analysis in three brain regions and pituitary revealed that β1-type transcripts were more abundant in pituitary than the other β paralogs with slight differences between brain regions. Quantification of mRNA abundance in gills after a salinity challenge showed an activation of atp1b1a and atp1b1b at high salinity water (60 ppt) and atp1b3a and atp1b3b in response to low salinity (5 ppt). Transcriptional analysis during larval development showed specific expression patterns for each paralog. Moreover, no differences in the expression profiles between larvae cultivated at 10 and 35 ppt were observed except for atp1b4 with higher mRNA levels at 10 than 35 ppt at 18 days post hatch. Whole-mount in situ hybridization analysis revealed that atp1b1b was mainly localized in gut, pronephric tubule, gill, otic vesicle, and chordacentrum of newly hatched larvae. All these data suggest distinct roles of NKA β subunits in tissues, during development and osmoregulation with β1 subunits involved in the adaptation to hyperosmotic conditions and β3 subunits to hypoosmotic environments.