cis-Regulatory elements control tissue-specifc spatial and temporal patterns of gene expression, and changes in gene expression, most likely due to modifcations in the cis-regulatory modules, are believed to be one of the major developmental mechanisms driving evolutionary changes throughout Metazoa. The impressive diversity of limb morphologies across vertebrates is intriguing since the patterning mechanisms involved in limb development seem to be relatively conserved among the vertebrate taxa in which they have been studied. In Squamata (lizards, snakes, and amphisbaenians), the evolution of a snake-like form, with reduced limbs and elongated body, is a frequent trend that has originated convergently and independently in diverse lineages (the most obvious of those being the lineage from which snakes have originated), and several degrees of limb-reduced morphologies are observed among closely-related species. Understanding the evolution of a snake-like morphology has driven many phylogeny-based studies, however, the developmental mechanisms involved in such body plans modifcations have not yet been investigated. This work proposes to investigate comparatively the evolution of the developmental mechanisms associated with limb reduction in a phylogenetic group of lizards, with snakes, amphisbaenians, and other basal squamate lizards as outgroups, by looking at the cis-regulatory region of limb-patterning genes, namely Sonic Hedgehog (Shh) and the distal Hoxd genes (Hoxd10-13), both involved in patterning the anterior-posterior limb axis; the analysis will also involve functional assays in chick embryos to test for the regulatory potential of squamate regulatory regions. The results are expected to provide interesting insights on the evolutionary flexibility of the selective pressures that acted upon the developmental mechanisms that build reduced limb morphologies in squamates.
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