Partitioning of tissue expression accompanies multiple duplications of theNa plus /K+ ATPase alpha subunit gene

Vertebrate genomes contain multiple copies of related genes that arose thro ugh gene duplication. In the past it has been proposed that these duplicate d genes were retained because of acquisition of novel beneficial functions. A more recent model, the duplication-degeneration-complementation hypothes is (DDC), posits that the functions of a single gene may become separately allocated among the duplicated genes, rendering both duplicates essential. Thus far, empirical evidence for this model has been limited to the engrail ed and sox family of developmental regulators, and it has been unclear whet her it may also apply to ubiquitously expressed genes with essential functi ons for cell survival. Here we describe the cloning of three zebrafish a su bunits of the Na(+),K(+)-ATPase and a comprehensive evolutionary analysis o f this gene family. The predicted amino acid sequences are extremely well c onserved among vertebrates. The evolutionary relationships and the map posi tions of these genes and of other a-like sequences indicate that both tande m and ploidy duplications contributed to the expansion of this gene family in the teleost lineage. The duplications are accompanied by acquisition of clear functional specialization, consistent with the DDC model of genome ev olution.