CONTROL OF EPITHELIOMESENCHYMAL TRANSFORMATION .1. EVENTS IN THE ONSET OF NEURAL CREST CELL-MIGRATION ARE SEPARABLE AND INDUCIBLE BY PROTEIN-KINASE INHIBITORS

Neural tubes isolated from quail embryos prior to epitheliomesenchymal transformation (EMT) and neural crest (NC) cell migration, when expla nted onto fibronectin surfaces, replicated properties of normal NC mor phogenesis such as (i) cell outgrowth, (ii) loss of A-CAM (N-cadherin) junctions and adoption of mesenchymal form, and (iii) development of HNK-1 immunoreactivity. The timetable of property (i) was essentially normal but the outgrowing cells were initially mainly epithelial, unli ke NC outgrowth in vivo and in cultures of older neural tubes. Mesench ymal properties (ii) and (iii) were progressively and variably retarde d relative to the in vivo timetable. Achievement of these properties b y EMT was principally related to proximity to the neural tube and to p reexisting mesenchymal cells, rather than being related temporally to the outgrowth timetable. This EMT, combined with a higher mitotic rate in the mesenchyme cells, resulted in the outgrowth passing from mainl y epithelial at 16 hr to mainly mesenchymal at 48 hr in vitro. Immedia te precocious EMT and outgrowth of A-CAM negative mesenchymal cells fr om pre-EMT neural tubes was stimulated by the protein kinase inhibitor s staurosporine and bisindolymaleimide in a cycloheximide-independent manner. EMT could be induced not only on the dorsal (i.e., NC) side, b ut also on the ventral side of the neural tube, but the ventral cells were less sensitive than the dorsal cells, and with developmental age became still less sensitive while the dorsal cells became more sensiti ve. The results suggest that the complex events of EMT in the NC syste m are not obligatorily coregulated, can be triggered by epigenetic eve nts involving differential protein phosphorylation, and may be control led via intraneural signaling. (C) 1995 Academic Press, Inc.