Fig. 7. Models for transcriptional control of ensheathing glia formation. In ventral C. elegans CEPsh glia and in ventral vertebrate spinal cords, Nkx family and Pax6-related proteins regulate Olig-related gene expression. In dorsal C. elegans CEPsh glia and in dorsal vertebrate spinal cords, a Pax7-related protein may promote Olig expression. Gray shading of the VAB-3 PD and HD reflects increased VAB-3 PD requirement in dorsal CEPsh glia for hlh-17 expression. The homeodomain of VAB-3 is preferentially required in ventral glia for expression of ptr-10, suggesting a possible similar preference for hlh-17. In addition to regulation by VAB-3 and MLS-2, HLH-17 regulates its own expression.