The Distal-less homeobox (Dlx) genes encode homeodomain transcription factors found in all animals of the phylum Chordata. These genes are involved in early vertebrate development of limbs, sensory organs, branchial arches and the forebrain (telencephalon and diencephalon). The mouse and human genomes each have six Dlx genes organized into convergently transcribed bigene clusters (Dlx1/2, Dlx3/4 and Dlx5/6). In the forebrain, Dlx1/2 and Dlx5/6 genes play essential roles in GABAergic neuron proliferation, migration and survival. Each bigene cluster includes a short intergenic region (~3.5-16kb) harboring cis-regulatory elements (CREs) that control expression of the Dlx genes. The Dlx1/2 intergenic region harbors the I12b/I12a CREs, while Dlx5/6 includes I56i/I56ii. In determining the regulatory roles of the CREs on Dlx activity and forebrain development, I have characterized the phenotypic changes that occur in mice that have an I56i enhancer deletion. I have also characterized mice with double deletions of I56i and I12b as well as mice that harbored an I12b deletion and have a SNP in the I56i enhancer (vI56i). Mutant mice with a single targeted deletion of I56i are viable, fertile and do not show obvious developmental defects. These mice have significant decreases in Dlx5/6, Gad1/Gad2 and Evf-2 expression in the forebrain and have defects related to GABAergic neuron development. The ΔI56i mutants demonstrate a behavioral phenotype related to anxiety and learning deficits. Mice that lack the I12b enhancer and have the vI56i do not show morphological abnormalities but have severely disrupted Dlx expression. When mice are homozygous for the I56i and I12b enhancer deletion, they do not survive past post natal day 5 and exhibit a dwarfed body size. These mice look weak and seem to have limited motor ability. In characterizing mice with targeted deletions of highly conserved Dlx enhancers, we will have a better understanding of forebrain development.

The Distal-less homeobox (Dlx) genes encode homeodomain transcription factors found in all animals of the phylum Chordata. These genes are involved in early vertebrate development of limbs, sensory organs, branchial arches and the forebrain (telencephalon and diencephalon). The mouse and human genomes each have six Dlx genes organized into convergently transcribed bigene clusters (Dlx1/2, Dlx3/4 and Dlx5/6). In the forebrain, Dlx1/2 and Dlx5/6 genes play essential roles in GABAergic neuron proliferation, migration and survival. Each bigene cluster includes a short intergenic region (~3.5-16kb) harboring cis-regulatory elements (CREs) that control expression of the Dlx genes. The Dlx1/2 intergenic region harbors the I12b/I12a CREs, while Dlx5/6 includes I56i/I56ii. In determining the regulatory roles of the CREs on Dlx activity and forebrain development, I have characterized the phenotypic changes that occur in mice that have an I56i enhancer deletion. I have also characterized mice with double deletions of I56i and I12b as well as mice that harbored an I12b deletion and have a SNP in the I56i enhancer (vI56i). Mutant mice with a single targeted deletion of I56i are viable, fertile and do not show obvious developmental defects. These mice have significant decreases in Dlx5/6, Gad1/Gad2 and Evf-2 expression in the forebrain and have defects related to GABAergic neuron development. The ΔI56i mutants demonstrate a behavioral phenotype related to anxiety and learning deficits. Mice that lack the I12b enhancer and have the vI56i do not show morphological abnormalities but have severely disrupted Dlx expression. When mice are homozygous for the I56i and I12b enhancer deletion, they do not survive past post natal day 5 and exhibit a dwarfed body size. These mice look weak and seem to have limited motor ability. In characterizing mice with targeted deletions of highly conserved Dlx enhancers, we will have a better understanding of forebrain development.

The vertebrate Dlx gene family consists of multiple convergently transcribed bigene clusters and encodes a group of homeodomain-containing transcription factors crucial for the development of forebrain, branchial arches, sensory organs and limbs. At least four cis-regulatory elements (CREs) are responsible for Dlx expression in the forebrain: URE2 and I12b in the Dlx1/Dlx2 (zebrafish dlx1a/dlx2a) locus, and, I56i and I56ii in the Dlx5/Dlx6 (zebrafish dlx5a/dlx6a) locus. Here, we first show that unlike the other three enhancers, mouse I56ii CRE targets a group of GABAergic projection neurons expressing striatal markers Meis2 and Islet1. Meis2 and Islet1 proteins can activate reporter gene transcription via the I56ii CRE, suggesting that they may be potential upstream regulators of Dlx genes in vivo. To determine whether there exists a dlx-mediated regulatory pathway during zebrafish GABAergic neuron formation, we establish two independent lines of transgenic fish in which the GFP reporter gene is controlled by a 1.4kb dlx5a/dlx6a intergenic sequence (encompassing zebrafish I56i and I56ii) and a 1.1kb fragment containing only I56i CRE, respectively. Our observations reveal that dlx5a/dlx6a regulatory elements exhibit a fairly specific activity in the zebrafish forebrain and may be essential for GABAergic neuron generation, while I56i and I56ii are likely to play distinct roles in modulating this process in different subpopulations of cells. Disruption of dlx1a/dlx2a or dlx5a/dlx6a function leads to a marked decrease of enhancer activity in the diencephalon and midbrain as well as a comparatively lesser extent of reduction in the telencephalon. In order to define the specific contribution of various individual CREs to overall Dlx regulation, we also generate a mutant mouse model in which I12b CRE is selectively deleted. Despite that mice homozygous for I12b loss develop normally and harbor no overt morphological defects in the forebrain, targeted deletion of this enhancer results in a significant reduction of Dlx1/Dlx2 transcript levels and seemingly perturbs cell proliferation in the subpallial telencephalon, particularly in the ventricular and subventricular zones of ganglionic eminences. Taken together, these data illustrate a complex and dynamic Dlx regulation in the early developing forebrain through the implications of multiple Dlx CREs with overlapping and diverse functions.

The vertebrate Dlx gene family consists of multiple convergently transcribed bigene clusters and encodes a group of homeodomain-containing transcription factors crucial for the development of forebrain, branchial arches, sensory organs and limbs. At least four cis-regulatory elements (CREs) are responsible for Dlx expression in the forebrain: URE2 and I12b in the Dlx1/Dlx2 (zebrafish dlx1a/dlx2a) locus, and, I56i and I56ii in the Dlx5/Dlx6 (zebrafish dlx5a/dlx6a) locus. Here, we first show that unlike the other three enhancers, mouse I56ii CRE targets a group of GABAergic projection neurons expressing striatal markers Meis2 and Islet1. Meis2 and Islet1 proteins can activate reporter gene transcription via the I56ii CRE, suggesting that they may be potential upstream regulators of Dlx genes in vivo. To determine whether there exists a dlx-mediated regulatory pathway during zebrafish GABAergic neuron formation, we establish two independent lines of transgenic fish in which the GFP reporter gene is controlled by a 1.4kb dlx5a/dlx6a intergenic sequence (encompassing zebrafish I56i and I56ii) and a 1.1kb fragment containing only I56i CRE, respectively. Our observations reveal that dlx5a/dlx6a regulatory elements exhibit a fairly specific activity in the zebrafish forebrain and may be essential for GABAergic neuron generation, while I56i and I56ii are likely to play distinct roles in modulating this process in different subpopulations of cells. Disruption of dlx1a/dlx2a or dlx5a/dlx6a function leads to a marked decrease of enhancer activity in the diencephalon and midbrain as well as a comparatively lesser extent of reduction in the telencephalon. In order to define the specific contribution of various individual CREs to overall Dlx regulation, we also generate a mutant mouse model in which I12b CRE is selectively deleted. Despite that mice homozygous for I12b loss develop normally and harbor no overt morphological defects in the forebrain, targeted deletion of this enhancer results in a significant reduction of Dlx1/Dlx2 transcript levels and seemingly perturbs cell proliferation in the subpallial telencephalon, particularly in the ventricular and subventricular zones of ganglionic eminences. Taken together, these data illustrate a complex and dynamic Dlx regulation in the early developing forebrain through the implications of multiple Dlx CREs with overlapping and diverse functions.

The vertebrate Dlx gene family consists of multiple convergently transcribed bigene clusters and encodes a group of homeodomain-containing transcription factors crucial for the development of forebrain, branchial arches, sensory organs and limbs. At least four cis-regulatory elements (CREs) are responsible for Dlx expression in the forebrain: URE2 and I12b in the Dlx1/Dlx2 (zebrafish dlx1a/dlx2a) locus, and, I56i and I56ii in the Dlx5/Dlx6 (zebrafish dlx5a/dlx6a) locus. Here, we first show that unlike the other three enhancers, mouse I56ii CRE targets a group of GABAergic projection neurons expressing striatal markers Meis2 and Islet1. Meis2 and Islet1 proteins can activate reporter gene transcription via the I56ii CRE, suggesting that they may be potential upstream regulators of Dlx genes in vivo. To determine whether there exists a dlx-mediated regulatory pathway during zebrafish GABAergic neuron formation, we establish two independent lines of transgenic fish in which the GFP reporter gene is controlled by a 1.4kb dlx5a/dlx6a intergenic sequence (encompassing zebrafish I56i and I56ii) and a 1.1kb fragment containing only I56i CRE, respectively. Our observations reveal that dlx5a/dlx6a regulatory elements exhibit a fairly specific activity in the zebrafish forebrain and may be essential for GABAergic neuron generation, while I56i and I56ii are likely to play distinct roles in modulating this process in different subpopulations of cells. Disruption of dlx1a/dlx2a or dlx5a/dlx6a function leads to a marked decrease of enhancer activity in the diencephalon and midbrain as well as a comparatively lesser extent of reduction in the telencephalon. In order to define the specific contribution of various individual CREs to overall Dlx regulation, we also generate a mutant mouse model in which I12b CRE is selectively deleted. Despite that mice homozygous for I12b loss develop normally and harbor no overt morphological defects in the forebrain, targeted deletion of this enhancer results in a significant reduction of Dlx1/Dlx2 transcript levels and seemingly perturbs cell proliferation in the subpallial telencephalon, particularly in the ventricular and subventricular zones of ganglionic eminences. Taken together, these data illustrate a complex and dynamic Dlx regulation in the early developing forebrain through the implications of multiple Dlx CREs with overlapping and diverse functions.

The vertebrate Dlx gene family consists of multiple convergently transcribed bigene clusters and encodes a group of homeodomain-containing transcription factors crucial for the development of forebrain, branchial arches, sensory organs and limbs. At least four cis-regulatory elements (CREs) are responsible for Dlx expression in the forebrain: URE2 and I12b in the Dlx1/Dlx2 (zebrafish dlx1a/dlx2a) locus, and, I56i and I56ii in the Dlx5/Dlx6 (zebrafish dlx5a/dlx6a) locus. Here, we first show that unlike the other three enhancers, mouse I56ii CRE targets a group of GABAergic projection neurons expressing striatal markers Meis2 and Islet1. Meis2 and Islet1 proteins can activate reporter gene transcription via the I56ii CRE, suggesting that they may be potential upstream regulators of Dlx genes in vivo. To determine whether there exists a dlx-mediated regulatory pathway during zebrafish GABAergic neuron formation, we establish two independent lines of transgenic fish in which the GFP reporter gene is controlled by a 1.4kb dlx5a/dlx6a intergenic sequence (encompassing zebrafish I56i and I56ii) and a 1.1kb fragment containing only I56i CRE, respectively. Our observations reveal that dlx5a/dlx6a regulatory elements exhibit a fairly specific activity in the zebrafish forebrain and may be essential for GABAergic neuron generation, while I56i and I56ii are likely to play distinct roles in modulating this process in different subpopulations of cells. Disruption of dlx1a/dlx2a or dlx5a/dlx6a function leads to a marked decrease of enhancer activity in the diencephalon and midbrain as well as a comparatively lesser extent of reduction in the telencephalon. In order to define the specific contribution of various individual CREs to overall Dlx regulation, we also generate a mutant mouse model in which I12b CRE is selectively deleted. Despite that mice homozygous for I12b loss develop normally and harbor no overt morphological defects in the forebrain, targeted deletion of this enhancer results in a significant reduction of Dlx1/Dlx2 transcript levels and seemingly perturbs cell proliferation in the subpallial telencephalon, particularly in the ventricular and subventricular zones of ganglionic eminences. Taken together, these data illustrate a complex and dynamic Dlx regulation in the early developing forebrain through the implications of multiple Dlx CREs with overlapping and diverse functions.