Figure 1

Dact genes are a chordate innovation. Diagram showing the Dact genes found in the database searches of the main chordate taxa. The gene family is exclusive to gnathostome and cyclostome vertebrates and cephalochordates, suggesting that these genes arose in the deuterostome lineage when chordates evolved. In the lancelet only one dact gene was found, while at least four different dact genes (dactA-D) were recognized in cyclostomes. Gnathostome Dact genes fell into four distinct paralog groups (Dact1-4), resulting from two rounds of genome duplications (1R, 2R). Teleost fish showed two dact3-related paralogs, the only duplicates generated by 3R that have been maintained in extant species. An intronless dact4-related gene was revealed in the gar and the zebrafish, probably having been retrotranscribed in the actinopterygian lineage before the holost-teleost split. Interestingly, the four gnathostome Dact groups are distinct from the four cyclostome dact genes, suggesting independent duplications in the cyclostome and gnathostome lineage. Dact genes identified in this study are represented by filled boxes; gene loss is indicated by a crossed box, gene locus loss by a singular cross. For the sake of simplicity, the loss of genes or loci generated during teleost 3R is not indicated. § No sequence information available. *1 Four distinct sets of dact sequences and additional short sequence stretches. *2 Insufficient sequence information to allow a conclusive analysis of the number of paralogs. *3 Gar and zebrafish have a second, intronless dact4 gene that possibly was retrotranscribed. *4 Large sequence gaps on the stickleback chromosome carrying the dact3b locus. *5Insufficient sequence information for lungfish; however a Dact2 gene was found for Protopterus aethiopicus.