Control of epitheliomesenchymal transformation. I. 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 explanted onto fibronectin surfaces, replicated properties of normal NC morphogenesis 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, unlike NC outgrowth in vivo and in cultures of older neural tubes. Mesenchymal properties (ii) and (iii) were progressively and variably retarded relative to the in vivo timetable. Achievement of these properties by EMT was principally related to proximity to the neural tube and to preexisting 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 mainly epithelial at 16 hr to mainly mesenchymal at 48 hr in vitro. Immediate precocious EMT and outgrowth of A-CAM negative mesenchymal cells from pre-EMT neural tubes was stimulated by the protein kinase inhibitors staurosporine and bisindolymaleimide in a cycloheximide-independent manner. EMT could be induced not only on the dorsal (i.e., NC) side, but 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 sensitive. The results suggest that the complex events of EMT in the NC system are not obligatorily coregulated, can be triggered by epigenetic events involving differential protein phosphorylation, and may be controlled via intraneural signaling.