Phenotype Characterization of Mice with Targeted Deletions of Dlx Enhancers

Abstract

The Distal-less homeobox (Dlx) genes encode a group of transcription factors that are involved in early vertebrate development of limbs, sensory organs, branchial arches and the forebrain. In the forebrain, four Dlx genes, Dlx1, Dlx2, Dlx5, Dlx6, play essential role in the differentiation and proper migration of GABAergic interneurons to the cortex. Dlx genes are organized in convergently transcribed bigene clusters and each cluster includes a short intergenic region harboring cis-regulatory elements (CREs): specifically, the Dlx1/2 cluster includes I12b and I12a CREs, while Dlx5/6 harbors I56i and I56ii. In an effort to determine the regulatory role of the CREs on Dlx expression and forebrain development, I characterized mice with an I56i deletion and both I12b and I56i deletions. At late embryonic stage (E18.5) and the adult stage (P35), both mutants had similar expression levels of Dlx2 and Gad2 gene, encoding enzyme glutamic acid decarboxylase that is responsible for synthesis of GABA. Mutant mice showed impaired expression levels of Dlx5. The expression levels of Gad1 were decreased in ΔI56i mutants but increased in ΔI12b/I56i mutants at E18.5, and both adult mutants had comparable expression of Gad1 as wildtype mice. Together with previous in situ hybridization results of mice at earlier stages (E11.5, E14.5), my data show that Dlx CREs have different levels of activity in regulating the expression of Dlx genes at different developmental stages. The mutations of I56i and I12b CREs did not affect the development of two subtypes of GABAergic neurons (calbindin and calretinin expressing neurons) in the forebrain. Compared to wildtype mice, both mutants had hypersociability and deficits of memory and learning ability. This opens the possibility that the deletions of Dlx intergenic CREs caused some developmental abnormalities and, therefore affected the behavior of the mice. Through studying the mice lacking Dlx intergenic CREs, I gained a better understanding of the role that I56i and I12b play in the regulation of the expression of Dlx genes, the development of GABAergic neurons, and the social and cognitive behavior.