The DLX Gene Family and Vertebrate Evolution: Insights from Lampreys
Neidert, Adam H.
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The development of the embryonic head structure of vertebrates is an evolutionary hallmark that sets the clade apart from all other organisms. Agnathans Gawless vertebrates) and gnathostomes Gawed vertebrates) make up the taxon vertebrata. Agnathans are considered the more primitive vertebrates and retain more primitive characteristics. The agnathan taxa separated from the gnathostome evolutionary line fairly early on in the evolutionary time line and their morphology is considered to be most similar to the proto vertebrate common ancestor. Because of their phylogenetic position as agnathans, lampreys can serve as a modem day proxy for the common ancestor of all vertebrates and thus provide insight into the evolution of such gnathostome characteristics as the jawbone, larger tri-partite brain, and paired appendages. The Dlx gene family is an important marker for these gnathostome morphological innovations. By comparing the Dlx gene family in lampreys with the Dlx homologs in gnathostomes and cephalochordates, we can gain insight into the role of gene duplication in early vertebrate evolution and its subsequent affect on morphology. To this extent, we cloned two distinct lamprey Dlx orthologs. Expression of these lamprey Dlx orthologs is found in the developing forebrain, pharyngeal arches, neural crest cells, otic and olfactory placodes. Phylogenetic analysis indicates that these are outgroups to the two major clades of gnathostoine Dlx genes and are most likely more closely related to the Dlx genes in the protovertebrate common ancestor.With honors.