Interposition of a new ruga depends on the distance between previously formed rugae. (A) In wild type mouse adult palates, presence of ruga 7b, and in case of presence, full extension of ruga 7b, are correlated with higher distances between its neighbors, rugae 7 and 8. Pictures show the 3 possible states of ruga 7b: absent (no 7b), short (short 7b) or fully developed (full 7b). Adult half palates of wild type mice were distributed into three classes according to ruga 7b state and the inter-rugae distance between rugae 7 and 8 was measured (see material and methods for details). For each class, the graphics shows the mean inter-rugae distance value (red line), the standard deviation (white rectangle) and the range of variation (vertical black line). (B) In a model where a new ruga can only form at a threshold distance from pre-existing rugae, the shape of "ruga n" allows prediction of that of ruga "n+1". A simplified scheme of ruga "n+1" interposition is shown with ruga n, ruga 8 (in black) and the new ruga "n+1" (in red). In the model, formation of ruga is only allowed at a threshold distance from pre-existing rugae, i.e. out of grayed fields. An abnormal shape of ruga "n" (black arrow) will change the shape of the grayed field, and consequently the shape of ruga "n+1" (color arrow). (C – I) In EdaTa embryos, propagation of ruga shape anomalies from ruga "n" to ruga "n+1" fit with the previous model. The pictures show half palates of ED14.5–15.0 embryos heterozygous (C, E – I) or homozygous (D) for the EdaTa mutation and hybridized with Shh probe. As in B, paired arrows point the abnormal shape of ruga "n" (black arrow) and the associated abnormal shape of ruga "n+1" (color arrow, color according to B). For each picture, scale bar is 500 μm.