Xmeis1, a protooncogene involved in specifying neural crest cell fate in Xenopus embryos

Meis1 (Myeloid Ecotropic viral Integration Site 1) is a homeobox gene that was originally isolated as a common site of viral integration in myeloid tu mors of the BXH-2 recombinant inbred mice strain. We previously isolated a Xenopus homolog of Meis1 (Xmeis1), Here we show that Xmeis1 may play a sign ificant role in neural crest development. In developing Xenopus embryos, Xm eis1 displays a broad expression pattern, but strong expression is observed in tissue of neural cell fate, such as midbrain, hindbrain, the dorsal por tion of the neural tube, and neural crest derived branchial arches. In anim al cap explants, overexpression of Xmeis1b, an alternatively spliced form o f Ymeis1, induces expression of neural crest marker genes in the absence of mesoderm, Moreover, Xmeis1b induces XGli-3 and XZic3, pre-pattern genes in volved at the earliest stages of neural crest development, and like these t wo genes, can induce ectopic pigmented cell masses when overexpressed in de veloping embryos. Misexpression of Ymeis1b also induces ectopic expression of neural crest markers along the antero-posterior axis of the neural tube in developing Xenopus embryos. In contrast, Xmeis1a, another splice variant , is much less effective at inducing these effects. These data suggest that Xmeis1b is involved in neural crest cell fate specification during embryog enesis, and can functionally intersect with the Gli/Zic signal transduction pathway.