Vol. 46 No. 6, 2007

Molecular Evolution and Phylogeny of Actin Genes in Haliotis Species (Mollusca: Gastropoda)

Frank Y.T. Sin*, Maxine J. Bryant, and Alice Johnstone

School of Biological Sciences, University of Canterbury, Christchurch, Private Bag 4800, New Zealand

Frank Y.T. Sin, Maxine J. Bryant, and Alice Johnstone (2007) Gene conversion and positive selection have been implicated as possible mechanisms involved in the evolution of actin genes in some marine organisms. We analyzed the molecular characteristics of 3 fully sequenced complementary (c)DNA and 3 partially sequenced cDNA of the actin gene family of the abalone, Haliotis iris Martyn (1784) (Mollusca: Gastropoda), 3 partially sequenced genomic DNAs of H. virginea Gmelin (1791), and actin gene sequences of H. rufescens Swainson (1822) and H. discus hannai Ino (1952) retrieved from GenBank to determine the possible evolutionary mechanism of this gene family in haliotids. There was no evidence to support either gene conversion or positive selection in the evolution of the actin gene family in haliotids. However, codon usage bias was evident in the actin gene family of these 4 haliotids. Phylogenetic analysis of the actin gene family revealed 2 distinct clades with H. iris actins A1, A1a, A1b, and A1c, H. virginea A1, A2, and A3, and H. rufescens actin in 1 clade and H. discus actin and H. iris actins A2 and A3 in the 2nd clade. In the expression analysis of actin genes, H. iris A1, A2, and A3 showed that these genes were expressed in all muscular structures (mantle musculature, foot, and retractor muscle) and non-muscular structures (gills and gonads) of adult H. iris, suggesting that they are all cytoplasmic-type actins. The lack of phylogenetic separation of actin genes into cytoplasmic and muscle actins and the absence of muscle-specific expression of actin genes may reflect the primitive taxonomic status of haliotids. The role of actin genes as genetic markers is discussed.

Key words: Actin, Gene family evolution, Nucleotide bias, Codon usage, Haliotis.

*Correspondence: Tel: 64-3-3642039. Fax: 64-3-3642024. E-mail:frank.sin@canterbury.ac.nz