Figure 2

Shh expression in three distinct signaling domains (MS, R2, M1) in Spry2;Spry4 samples. Shh expression in three distinct signaling domains: MS (blue bar), R2 (red bar) and M1 (yellow bar), was sequentially detected in the cheek region of embryonic mandibles in nine various Spry2;Spry4 mouse genotypes according to embryonic body weights. (A) The supernumerary tooth formation is dependent on decreasing dosages of Spry2 and Spry4 genes. The samples with higher Spry2;Spry4 gene dosages showed merging (purple frames) of R2 and early M1 Shh signaling domains into one expression domain (pEK) located in the center of M1 germ. In contrast, samples with lower Spry2;Spry4 gene dosages did not evince any merging. Instead of this, they showed a supernumerary tooth primordium which arose from persisting R2 with its own Shh signaling domain. (B) The prolongation of Shh expression was strengthened with decreasing Spry2 gene dosage. The prolongation of Shh expression in preceding signaling domain implies later start of subsequent expression domain. Black arrowheads represent the moment where the early M1 Shh signaling domain appeared and it co-existed transiently with the persisting Shh expression in R2. Dashed black line suggests the trend of prolongation of Shh expression in R2 rudiment according to decreasing Spry2 gene dosage. The colored frames (blue, red and yellow) represent referential presence of signaling domains of MS (blue), R2 (red) and M1 (yellow) observed in WT mice [4]. The green dashed line is a reference line representing M2 (second molar) signaling center appearance in control genotype (Spry2+/+;Spry4+/+). The density of harvested embryos is shown by dots in bars. Pink dots represent embryos with supernumerary tooth germ formation. Orange arrow determines continuation of yellow bar given by harvested material with higher body-weight out of the graph field. Gaps between colored bars mean absence of material.