The evolution of class I ADH genes in primates

Abstract

The alcohol dehydrogenase (ADH) gene family is widespread throughout the animal kingdom and plays a crucial role in oxidizing different types of alcohol. In mammals, this gene family has undergone multiple duplications, resulting in a group of genes that can be classified into six classes. Class I ADH duplication is characteristic of primates and the enzyme can work not only as a homodimer but also as a heterodimer. Therefore, having more class I ADH genes possibly lead to forming variable dimers which contribute to a variety of kinds or concentration of alcohol oxidization. Some previous studies hypothesized that class I gene evolution might be related to the adaptation of fermented fruit eating because the genes mainly play a role in ethanol digestion in the human liver. Although such studies have shown that the copy number varied between primate species, there are very few studies showing the phylogenetic relationship of the duplicated genes that must give a good hint of adaptive evolution. We assessed the number of class I ADH genes in primates using blast+, constructed the phylogenetic tree, and translated the genes in silico to estimate the number of pseudogenes. Our results suggest that the phylogenetic topology was coincident with the previous reports in that genes formed a clade respectively in the infraorder level. Notably, we found that the gene loss occurred in langurs and pseudogenization occurred in tarsiers and red slender loris, suggesting that alcohol metabolization might not be as important for folivores and insectivores as it is for frugivores.