Fig. 5. Model for the role of FoxM1 in primary neuronal differentiation in Xenopus embryos. BMP inhibition induces not only neural induction but also FoxM1 expression during gastrulation. FoxM1 activates the expression of G2-M cell-cycle regulators, such as Cdc25B and cyclin B3, and thereby drives the immediate, preceding cell division(s) of neuronal precursors for their differentiation. The temporal expression patterns of Cdc25B and cyclin B3 are from Fig. 4A and Fig. S4A in the supplementary material, whereas those of Sox2, Xngnr1, N-CAM and N-tubulin are from the published literature (as cited in the text) and Fig. S5 in the supplementary material. The final division (^*) of neuronal precursors presumably occurs between st. 13 and 16, depending on the cells (Hartenstein, 1989), but mainly around st. 13 (Lamborghini, 1980). MBT, midblastula transition; G2/M, G2-M transition of the cell cycle; Hpf, hours post-fertilization.