Perturbation of Hoxb5 signaling in vagal and trunk neural crest cells causes apoptosis and neurocristopathies in mice

M K M Kam,E W Y Sat,J J Zhu,V C H Lui,M C H Cheung,W W C Cheng,P K H Tam

doi:10.1038/cdd.2013.142

Abstract

Neural crest cells (NCCs) migrate from different regions along the anterior-posterior axis of the neural tube (NT) to form different structures. Defective NCC development causes congenital neurocristopathies affecting multiple NCC-derived tissues in human. Perturbed Hoxb5 signaling in vagal NCC causes enteric nervous system (ENS) defects. This study aims to further investigate if perturbed Hoxb5 signaling in trunk NCC contributes to defects of other NCC-derived tissues besides the ENS. We perturbed Hoxb5 signaling in NCC from the entire NT, and investigated its impact in the development of tissues derived from these cells in mice. Perturbation of Hoxb5 signaling in these NCC resulted in Sox9 downregulation, NCC apoptosis, hypoplastic sympathetic and dorsal root ganglia, hypopigmentation and ENS defects. Mutant mice with NCC-specific Sox9 deletion also displayed some of these phenotypes. In vitro and in vivo assays indicated that the Sox9 promoter was bound and trans-activated by Hoxb5. In ovo studies further revealed that Sox9 alleviated apoptosis induced by perturbed Hoxb5 signaling, and Hoxb5 induced ectopic Sox9 expression in chick NT. This study demonstrates that Hoxb5 regulates Sox9 expression in NCC and disruption of this signaling causes Sox9 downregulation, NCC apoptosis and multiple NCC-developmental defects. Phenotypes such as ENS deficiency, hypopigmentation and some of the neurological defects are reported in patients with Hirschsprung disease (HSCR). Whether dysregulation of Hoxb5 signaling and early depletion of NCC contribute to ENS defect and other neurocristopathies in HSCR patients deserves further investigation.

Highlights

The different combinations of Hox genes expressed in these domains are mirrored in the Neural crest cells (NCCs) derived from those domains.[14,15,16] So far, our knowledge regarding the role of Hox genes during NCC development comes mostly from lossof-function experiments, the overlapping expression and extensive functional redundancy among Hox genes preclude detailed investigations of the developmental functions of individual Hox genes in this way
We studied the effects on the development of NCC and NCC-derived structures
We used mice expressing a dominant-negative form of Hoxb[5] in NCC from all along the neural tube (NT) to investigate the impact of abnormal Hoxb[5] signaling in the development of NCC-derived tissues

Summary

Introduction

The different combinations of Hox genes expressed in these domains are mirrored in the NCC derived from those domains.[14,15,16] So far, our knowledge regarding the role of Hox genes during NCC development comes mostly from lossof-function experiments, the overlapping expression and extensive functional redundancy among Hox genes preclude detailed investigations of the developmental functions of individual Hox genes in this way. To circumvent the problem of functional redundancy and investigate the function of Hoxb[5] in NCC, we generated transgenic mice that express a dominant-negative chimeric protein, engrailed-Hoxb[5] (enb5), upon Cre-induction. This enb[5] repressor competes with Hoxb[5] for binding to target genes, thereby disrupting the developmental pathways that require Hoxb[5]. We showed that Hoxb[5] regulates the expression of Sox[9] in trunk NCC, and that perturbation of Hoxb[5] signaling in NCC causes downregulation of Sox[9], apoptosis of NCC and neurocristopathies in mice

Objectives

Methods

Results

Conclusion