Fig. 10. Schematics of a possible mode of Hoxd10 induction. At stage 13, a prepattern for Hoxd10 expression is present in the anterior LS neural tube. The most anterior LS segments (LS1-2) have less ability to develop high levels of Hoxd10 expression than more posterior segments (LS3+). This gradient of competence may reflect exposure to a very early gradient of inducing signals, in extreme posterior embryonic regions. At stage 13+, inducing signals may spread anteriorly, as far as posterior T regions, stabilizing and amplifying the LS prepattern. Associated with this process is an anterior extension of non-axial mesoderm and a posterior elongation of the LS neural tube (arrows, after Catala et al., 1995). The asterisks denote displacement of mesoderm at one axial level.