LEE, S.E.: Examining the evolution of gene sequence and function: The Distal-less (Dlx ) homeodomain ?family?.

The homeodomain-containing gene Distal-less (Dll ) is a transcription factor known to be important in proximo-distal axes and nervous system patterning in Drosophila. Dll gene sequence orthologues have been identified from several invertebrates including members of the phyla Cnidaria, Mollusca, Arthropoda, Urochordata, Hemichordata, and Cephalochordata. Multiple orthologues (Dlx genes) have been reported from vertebrate model systems, reflecting duplication events within those lineages. While several review-type discussions of the Dll/Dlx gene family have covered aspects of the conservation and evolution of these genes (e.g. Beanan and Sargent 2000; Panganiban 2000; Stock et al. 1996), a review of the sequence and functional evolution of these genes across the metazoa is lacking. Here I present an investigation of the sequence evolution of the DllDlx genes through parsimony analyses, and discuss problems with gene naming, duplication events, and phyletic gaps in data within such a context. In addition, I summarize functional information from both true function and correlative expression data and map these gene functions onto phylogenetic trees. This exercise provides the backdrop for a discussion of gene function evolution. Through an exploration of developmental processes (separate from developing structures), I ask the question- what are the possible proto-functions for this gene group? The answer may include involvement with mesenchymal-epithelial interactions, cell shape changes, cell-cell communication, and/or adhesion processes.