Fig. 5: The spatio-temporal dynamics of activation-inhibition mechanisms has co-evolved in mouse molars.

a Duration of each stage estimated by Markov models from Fig. 1b. Numbers in triangles as in b. Timeline and cartoons on the right recapitulate changes in signalling centres. b Expression of Bmp4 is more focalized in mouse than in hamster SEKs. Mouse and hamster samples are paired for similar advancement of epithelial growth. Age of samples in days is in the upper molar picture (for samples taken from the same embryo) or in both pictures (samples taken from different embryos). See also Supplementary Fig. 6.c Mouse molars transition earlier to cusp patterning. Transition from the PEK ( = 0 in the matched timeline) to the 2-SEK stage as seen on tooth germ epithelial parts hybridised against Fgf4. Pairs of mouse/hamster embryos were selected to show four remarkable steps in this chronology (1–4 in triangles). At stage 2, Fgf4 expression is still elongated in hamster, as typical for a PEK, while it is already roundish in mouse, as typical for a SEK.