SHH signaling directed by two oral epithelium-specific enhancers controls tooth and oral development

Tomoko Sagai,Toshihiko Shiroishi,Takanori Amano,Sung-Won Cho,Hyejin Seo,Akiteru Maeno,Hiroshi Kiyonari

doi:10.1038/s41598-017-12532-y

Tomoko Sagai, Toshihiko Shiroishi + Show 5 more

Open Access

https://doi.org/10.1038/s41598-017-12532-y

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Abstract

Interaction between the epithelium and mesenchyme coordinates patterning and differentiation of oral cavity structures including teeth, palatal rugae and tongue papillae. SHH is one of the key signaling molecules for this interaction. Epithelial expression of Shh in the tooth buds and tongue papillae is regulated by at least two enhancers, MRCS1 and MFCS4. However, it is unclear how the two enhancers cooperate to regulate Shh. Here, we found that simultaneous deletion of MRCS1 and MFCS4 results in the formation of a supernumerary tooth in front of the first molar. Since deletion of either single enhancer barely affects tooth development, MRCS1 and MFCS4 evidently act in a redundant fashion. Binding motifs for WNT signaling mediators are shared by MRCS1 and MFCS4, and play a central role in regulating Shh expression, indicating that the two redundant enhancers additively exert their Shh regulation by responding to WNT signal input.

Highlights

During development of jawed vertebrates, pairs of pharyngeal arches form many oropharyngeal apparatuses including the lip, salivary glands, teeth, tongue and palate in the mandible and maxilla
Since single heterozygotes of either Shh coding sequence KO or MRCS1 KO mice have no defect in tooth development including formation of supernumerary teeth (Supplementary Table 1), the result clearly indicates that the observed tooth defect depends on SHH signaling, and that level of SHH signaling activity is crucial for formation of the supernumerary tooth
While more than half (~55%) of cells in the depth half region of the wild type were positive for the Shh nascent RNA, the nascent RNA positive cells in the same region were significantly reduced to 40% in the double KO (DKO) mouse (Fig. 2p) In the superficial half region, frequency of the nascent RNA positive cells was not significantly different between the wild type and DKO mice. These results showed that additive action of MRCS1 and MFCS4 are necessary for precise control of the expression level of Shh, these enhancers may be dispensable for the initiation of Shh expression in the tooth buds

Summary

Introduction

During development of jawed vertebrates, pairs of pharyngeal arches form many oropharyngeal apparatuses including the lip, salivary glands, teeth, tongue and palate in the mandible and maxilla. This result suggests that MRCS1 and MFCS4 direct Shh expression in the oral epithelium by responding to WNT signaling, and that mouse MRCS1 rather than MFCS4 has taken over the function of the ancestral MFCS4 during mammalian evolution. They exhibited formation of a supernumerary tooth, which was observed in the MRCS1 single KO mouse and in compound heterozygotes of the Shh coding sequence KO and MRCS1 KO alleles (Fig. 2a–h).

Results

Conclusion