FXYD Domain Containing Ion Transport Regulator 8 (FXYD8)

Based on the conserved domain of these small membrane proteins, eight expressed FXYD isoforms were identified. Phylogenetic analysis suggests that six isoforms are homologues to the previously identified FXYD2, FXYD5, FXYD6, FXYD7, FXYD8, and FXYD9, while two additional isoforms were found (FXYD11 and FXYD12). Using quantitative PCR, tissue-dependent expression of the different isoforms was analyzed in gill, kidney, intestine, heart, muscle, brain, and liver. Two isoforms were expressed in several tissues (FXYD5 and FXYD9), while six isoforms were distributed in a discrete manner. In excitable tissues, two isoforms were highly expressed in brain (FXYD6 and FXYD7) and one in skeletal muscle (FXYD8). In osmoregulatory tissues, one isoform was expressed predominantly in gill (FXYD11), one in kidney (FXYD2), and one equally in kidney and intestine (FXYD12).