PEEL, A.D.; AKAM, M.E.; University of Cambridge, U.K.; University of Cambridge, U.K.: The evolution of insect engrailed genes, and its implications for our understanding of gene family evolution.

A number of insect orders, including Diptera, Lepidoptera & Blattodea, have been shown to contain species that possess two engrailed genes. Conspecific engrailed genes typically group together in gene trees, which taken at face value implies that multiple engrailed gene duplications occurred during insect evolution. However, I will present data suggesting that the insect common ancestor possessed two engrailed genes, and that gene trees overestimate the number of duplication events that have taken place. Insect engrailed genes typically exhibit overlapping expression patterns, and it seems likely that functional differences are mediated, at least in part, by two protein domains always possessed by one paralogue, but not the other. These two domains are located 5′ to the homeodomain, where there has been significant sequence divergence between paralogues. However, in hemimetabolous insects, there appears to have been gene conversion between the 3′ homeobox regions of paralogues. It is not clear whether this reflects selection for and/or against gene conversion, or has resulted from failure of the more conserved 3′ regions to diverge rapidly enough to escape gene conversion. The homeobox regions of holometabolous and apterygote insects exhibit greater sequence divergence, but there is still evidence for sequence coevolution, reflected in misleading gene trees. I will discuss whether this is likely to result from selection for coevolution, or random genetic drift in association with regular gene conversion events. Given that many duplicates are thought to have been fixed as a result of divergence in regulatory, and not protein coding, sequence, these observations could have major implications for the reliability of gene trees, and therefore our understanding of gene family evolution.