The alpha-actinin gene family: a revised classification

The sequencing of a genome is the first stage of its complete characterization. Subsequent work seeks to utilize available sequence data to gain a better understanding of the genes which are found within a genome. Gene families comprise large portions of the genomes of higher vertebrates, and the available genomic data allow for a reappraisal of gene family evolution. This reappraisal will clarify relatedness within and between gene families. One such family, the alpha-actinin gene family, is part of the spectrin superfamily. There are four known loci, which encode alpha-actinins 1, 2, 3, and 4. Of the eight domains in alpha-actinin, the actin-binding domain is the most highly conserved. Here we present evidence gained through phylogenetic analyses of the highly conserved actin-binding domain that alpha-actinin 2 was the first of the four alpha-actinins to arise by gene duplication, followed by the divergence of alpha-actinin 3 and then alpha-actinins 1 and 4. Resolution of the gene tree for this gene family has allowed us to reclassify several alpha-actinins which were previously given names inconsistent with the most widely accepted nomenclature for this gene family. This reclassification clarifies previous discrepancies in the public databases as well as in the literature, thus eliminating confusion caused by continued misclassification of members of the alpha-actinin gene family. In addition, the topology found for this gene family undermines the 2R hypothesis theory of two rounds of genome duplication early in vertebrate evolution.