Fig. 1

Gene regulatory programs across serial organs. a Possible explanations for distinct serial organ programs. The beginning, the middle, and the ends of development are most conserved in the funnel, hourglass, and inverse hourglass models, respectively. b Morphologically, the mouse upper and lower molars are similar at the beginning of development but diverge as development progresses (upper panel). Their gene expression programs, however, are most distinct in the middle of their development. The largest axis of variation (the first principal component (PC1)) corresponds to time, and the second largest (the second principal component (PC2)) is consistent with the proportions of constituent tissue types (lower panel)