Two Na,K-ATPase β2 subunit isoforms are differentially expressed within the central nervous system and sensory organs during zebrafish embryogenesis

We have identified cDNAs encoding a second zebrafish ortholog of the human Na,K-ATPase β2 subunit. The β2b cDNA encodes a 292 amino acid-long polypeptide with 74% identity to the previously characterized zebrafish β2a subunit. By using a zebrafish meiotic mapping panel, we determined that the β2b gene (atp1b2b) was tightly linked to markers on linkage group 5, whereas the β2a gene was located on linkage group 23. In situ hybridization analysis shows that in developing zebrafish embryos, atp1b2a and atp1b2b are predominantly expressed in the nervous system. β2a transcripts were abundantly expressed throughout brain as well as spinal cord neurons and lateral line ganglia. In contrast, β2b mRNA expression was primarily detected in sensory organs, including retina, otic vesicles, and lateral line neuromast cells. These results suggest that the β2a and β2b genes play distinct roles in developing brain and sensory organs, and raise the possibility that the functions encoded by the single mammalian β2 gene may be partitioned between the two zebrafish β2 orthologs.