Functional Analysis of Dlx Intergenic Enhancers in the Developing Mouse Forebrain

Abstract

The Distal-less homeobox (Dlx) genes encode a group of transcription factors that are involved in various developmental processes including forebrain development. Dlx genes are arranged in convergently transcribed bigene clusters with enhancer sequences located in the intergenic region of each cluster. The expression patterns of Dlx1/Dlx2 and of Dlx5/Dlx6 are attributed in part to the activity of I12a/I12b and I56i/I56ii intergenic enhancers, respectively. In an effort to determine how Dlx intergenic enhancers interact with the promoter regions of each cluster, I employed the Chromosome Conformation Capture (3C) technique on developing forebrain at E13.5 and E15.5. My 3C analysis provided potential enhancer-promoter interaction, in cis, that are consistent with previously known regulatory mechanisms. Furthermore, trans interactions may exist between Dlx1/Dlx2 and Dlx5/Dlx6 clusters in the developing forebrain at E13.5, thus providing a possible novel cross-regulatory mechanism between these two loci. I have also investigated the phenotypic consequences of Dlx enhancer deletion(s) on forebrain development by characterizing mice with I56ii and I56ii/I12b enhancer deletions. Enhancer deletions significantly impair Dlx expression as well as that of Evf2, Gad2 and of the striatal markers Islet1 and Meis2. Enhancer deletion(s) also reduce the expression of ISLET1 and CTIP2 proteins and Semaphorin 3A, Slit1 and Ephrin A5 that are thought to provide guidance cues in the corridor cells. Overall, these changes may disrupt the guidance of the thalamocortical axons. The data presented here further our understanding of the interactions between Dlx intergenic enhancers and promoter regions. Enhancer deletion(s) furthers our understanding of Dlx regulatory networks necessary that ensure proper Dlx expression, which, in turn may be involved in a genetic pathway underlying the synthesis of GABA, which may be further essential in maintaining the GABAergic phenotype.