Sperber, Steven M2013-11-082013-11-0820042004Source: Dissertation Abstracts International, Volume: 66-05, Section: B, page: 2430.http://hdl.handle.net/10393/29169http://dx.doi.org/10.20381/ruor-12804The vertebrate Dlx homeodomain-containing genes are generally organized as three convergently transcribed bigene clusters. Paired genes share highly conserved overlapping expression patterns in the forebrain, the pharyngeal arches, sensory placodes and limb/fin buds. Little is known about how the Dlx genes are targeted to their sites of expression, or what particular roles individual genes play in development. In the pharyngeal arches, Dlx genes are expressed in a nested manner, which defines proximodistal identity. We identified two distinct cis-acting enhancers, I12a and I56i situated between Dlx1/2 and Dlx5/6 pairs respectively that regulate expression in the mandibular arch. In transgenic animals, the two enhancers targeted reporter gene expression to distinct populations of mesenchymal cells in the mandibular arch. Both enhancers responded to epithelial signaling cues, such as FGF8 and BMP4, similar to endogenous Dlx genes. Therefore, the combinatorial arch expression is achieved through interaction between signaling factors and intrinsic cellular factors. To investigate the individual roles of the paired Dlx1/2 gene in patterning the pharyngeal arches, we silenced zebrafish dlx1a and dlx2a using morpholino antisense oligonucleotides. Loss of dlx2a function in zebrafish embryos resulted in reductions of arch neural crest markers as well as perturbation of neurogenic and chondrogenic derivatives. Loss of dlx1a resulted in malformations of cartilage elements indicating a role in arch patterning. To explore further the evolution of the Dlx gene family, we characterized the Distal-less homologue, Odidll, in the protochordate species, Oikopleura dioica. Odidll is not part of a bigene cluster suggesting either that a paralogue was lost or that the tandem duplication event occurred subsequent to the species' divergence. Odidll, was expressed in ectodermally-derived tissues suggesting a role that may have been observed in a common chordate ancestor. These results contribute to our understanding of Dlx regulation, function and evolution.211 p.enBiology, Molecular.Thesis