Dlx Homeobox Genes Promote Cortical Interneuron Migration from the Basal Forebrain by Direct Repression of the Semaphorin Receptor Neuropilin-2

Trung N Le,David D Eisenstat,Jeffrey T Wigle,Guoyan Du,Mario Fonseca,Qing-Ping Zhou

doi:10.1074/jbc.m607486200

Trung N Le, David D Eisenstat + Show 4 more

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https://doi.org/10.1074/jbc.m607486200

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Abstract

Dlx homeobox genes play an important role in vertebrate forebrain development. Dlx1/Dlx2 null mice die at birth with an abnormal cortical phenotype, including impaired differentiation and migration of GABAergic interneurons to the neocortex. However, the molecular basis for these defects downstream of loss of Dlx1/Dlx2 function is unknown. Neuropilin-2 (NRP-2) is a receptor for Class III semaphorins, which inhibit neuronal migration. Herein, we show that Neuropilin-2 is a specific DLX1 and DLX2 transcriptional target by applying chromatin immunoprecipitation to embryonic forebrain tissues. Both homeobox proteins repress Nrp-2 expression in vitro, confirming the functional significance of DLX binding. Furthermore, the homeodomain of DLX1 and DLX2 is necessary for DNA binding and this binding is essential for Dlx repression of Nrp-2 expression. Of importance, there is up-regulated and aberrant expression of NRP-2 in the forebrains of Dlx1/Dlx2 null mice. This is the first report that DLX1 or DLX2 can function as transcriptional repressors. Our data show that DLX proteins specifically mediate the repression of Neuropilin-2 in the developing forebrain. As well, our results support the hypothesis that down-regulation of Neuropilin-2 expression may facilitate tangential interneuron migration from the basal forebrain.

Highlights

Expression at the pallial-subpallial boundary [1]
DLX1 and DLX2 Homeobox Proteins Bind to a Neuropilin-2 Promoter Region in Embryonic Forebrain in Vivo—Marin et al [15] established that the Class III semaphorins, semaphorins 3A and 3F, and their receptors, Neuropilin-1 and Neuropilin-2, play important roles in the sorting of interneurons that are migrating to the neocortex and the striatum
Control chromatin immunoaffinity purification (ChIP) assays performed without antibody or with anti-DLX antibodies and chromatin derived from embryonic hindbrain tissues where Dlx genes are not expressed were negative

Summary

Introduction

Expression at the pallial-subpallial boundary [1]. Insights into the functional role of Dlx genes in development have been primarily gained from analysis of the phenotypes of mice with targeted deletions of Dlx1/Dlx2 [5,6,7,8], Dlx5 [9], and Dlx5/Dlx6 [10]. Loss of Dlx and Dlx function leads to the increased and ectopic expression of Neuropilin-2 as subventricular ectopias in the medial and lateral ganglionic eminences These results support our hypothesis that a subpopulation of late-born Dlx-expressing interneurons (Neuropilin-2 low/non-expressing) successfully bypass semaphorin repulsive cues to migrate to the neocortex. Loss of Dlx and Dlx function results in increased and aberrant Neuropilin-2 expression in this population, and their resultant responsiveness to semaphorin signaling may contribute to block tangential interneuron migration from the basal telencephalon. These data delineate part of the molecular mechanism by which migrating interneurons may bypass inhibitory cues to reach their correct destinations in the forebrain

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