Xenopus HMGA2 is required for neural crest cell survival and migration

HMGA proteins are chromatin “architectural modifiers”, bearing three conserved “AT-hook” DNA binding motifs though which they assist in regulation of gene transcription. We have cloned Xenopus laevis hmga2β (Xhmga2β) and studied its developmental expression. By in situ hybridisation (ISH), localized transcripts are first detected at neurula stages, in the presumptive central nervous system (CNS) and eye field, and in the neural crest cell (NCC) presumptive territory. At tailbud and tadpole stages, Xhmga2β mRNA is detected in the CNS, in the otic vesicles, in migrating neural crest cell and their derivatives, in the notochord and in the medio-lateral mesoderm. In order to address the functional roles of Xhmga2β in the neural derivatives, we have injected morpholinos against Xhmga2β in a loss-of-function approach, targeting the morpholino to the dorsal region. Injected embryos typically show very strong abnormalities in the branchial region, where the branchial arches are lost or severely disrupted. Analysis of NCC molecular markers show severe downregulation or absence of Xtwist, and Xdll4 expression at the tailbud stage. TUNEL staining on injected embryos shows that extensive cell death occurs in the regions normally occupied by NCC. Injection of control morpholinos did not lead to similar alterations. The effects of the morpholino injection are rescued by coinjection of a synthetic Xhmga2β mRNA that is not targeted by the morpholino. These data suggest that Xhmga2β is required for NCC survival, possibly during the stage when NCC migrate in the visceral arches