Investigation of regulatory elements directing Dlx gene expression in the avian forebrain
There are six known mammalian 'Distal-less' type homeobox ('Dlx') genes, arranged in three convergently transcribed pairs. Highly conserved 'cis'-acting enhancer sequences have been identified in the 'Dlx1/2' and 'Dlx5/6' intergenic regions in zebrafish and mouse. 'Dlx3' and ' Dlx4' were originally thought not to be expressed in the forebrain of any vertebrate embryo; however expression of 'Dlx3' in the ventral forebrain of chick embryos has since been documented. Based on current models of 'Dlx' gene evolution it is unclear whether forebrain enhancers have been retained in the 'Dlx3/4' locus throughout the course of avian evolution or whether they were acquired after the divergence of birds from other vertebrate lineages. It is difficult to evaluate forebrain enhancer conservation in the avian lineage with the current available genome sequence. This thesis describes the isolation of a genomic clone containing a partial 'Dlx3' gene and sequences downstream, and the development of assays to test enhancer activity in chicken and zebrafish embryos.