Abstract
Hox proteins are a deeply conserved group of transcription factors originally defined for their critical roles in governing segmental identity along the antero-posterior (AP) axis in Drosophila. Over the last 30 years, numerous data generated in evolutionarily diverse taxa have clearly shown that changes in the expression patterns of these genes are closely associated with the regionalization of the AP axis, suggesting that Hox genes have played a critical role in the evolution of novel body plans within Bilateria. Despite this deep functional conservation and the importance of these genes in AP patterning, key questions remain regarding many aspects of Hox biology. In this commentary, we highlight recent reports that have provided novel insight into the origins of the mammalian Hox cluster, the role of Hox genes in the generation of a limbless body plan, and a novel putative mechanism in which Hox genes may encode specificity along the AP axis. Although the data discussed here offer a fresh perspective, it is clear that there is still much to learn about Hox biology and the roles it has played in the evolution of the Bilaterian body plan.
Highlights
Hox proteins are a group of homeodomain-containing transcription factors that are renowned for their roles in patterning animal body plans and for their remarkably deep evolutionary conservation
Homeodomain proteins are defined by the presence of a highly conserved DNA-binding region known as the homeodomain and are encoded by Homeobox genes
Homeobox genes are a large family of similar genes and can be divided into 11 different gene classes in animals, and the Hox genes belong to the ANTP class[1,2]
Summary
Hox proteins are a group of homeodomain-containing transcription factors that are renowned for their roles in patterning animal body plans and for their remarkably deep evolutionary conservation. The new data reported in Head and Polly challenge this assumption and instead suggest that the regionalized axial skeletons of limbed reptiles and other derived vertebrate taxa are descended from an axial plan that displayed very little regionalization in the first place[28] This hypothesis is supported by acquired fossil evidence from Paleozoic amniotes, including extinct stem members of Reptilia and Mammalia, that shows that these animals exhibited “deregionalized” axial skeletons with very subtle changes in their primaxial morphology[28]. Grant information The author(s) declared that no grants were involved in supporting this work
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