Fig. 11. Distinct modes of regulatory mechanisms of differentiation of the cranial and trunk neural crest cells. BMP2/4, GGF, TGFß1 and WNT1 act to induce neurogenesis, gliagenesis, myogenesis and melanogenesis, respectively, from the multipotent trunk neural crest stem cells (A) (Shah et al., 1996; Anderson, 1997; Sieber-Blum and Zhang, 1997; Zhang et al., 1997; Francis-West et al., 1998; Dunn et al., 2000). Inductive and repressive roles of the FGF2/8, BMP2/4, SHH, TGFß1 and WNT pathways on the cranial neural crest differentiation (B). The positive regulators are shown in red and the negative ones are in blue. FGF2/8 appears to be generally required for normal proliferation and survival of the cranial but not trunk neural crest. FGF2/8 also seem to be a positive regulator/survival factor for the melanogenic cells in both cranial and trunk crest cultures. Some of the markers used to identify the different cell types are shown in brackets. Some cell types, particularly smooth muscle cells and pigment cells, differentiate in the surviving cultures grown with media containing no purified exogenous proteins. It is not clear whether these cells rely on the residual factors present in the serum, such as a clearly detectable BMP-like activity, or represent a default state of the cranial neural crest differentiation.