Phylogenetic Analysis of Gene Structure and Alternative Splicing in a-Actinins

The a-actinins are an important family of actin-binding proteins with the ability to cross-link actin filaments when in dimer form. Members of the a-actinin family share a domain topology composed of highly conserved actin-binding and EF-hand domains separated by a rod domain composed of spectrin-like repeats. Functional diversity within this family has arisen through exon duplication and the formation of alternate splice isoforms as well as gene duplications during the evolution of vertebrates. In addition to the known functional domains, a-actinins also contain a consensus PDZ-binding site. The completed genome sequence of over 32 invertebrate species has allowed the analysis of gene structure and exon– gene duplication over a diverse range of phyla. Our analysis shows that relative to early branching metazoans, there has been considerable intron loss especially in arthropods with few cases of intron gains. The C-terminal PDZ-binding site is conserved in nearly all invertebrates but is missing in some nematodes and platyhelminths. Alternative splicing in the actin-binding domain is conserved in chordates, arthropods, and some nematodes and platyhelminths. In contrast, alternative splicing of the EF-hand domain is only observed in chordates. Finally, given the prevalence of exon duplications seen in the actin-binding domain, this may act as a significant mechanism in the modification of actin-binding properties. Key words: a-actinin, exon duplication, alternate splicing