Shh Plays an Inhibitory Role in Cusp Patterning by Regulation of Sostdc1

Abstract

Crown shapes in mammalian teeth vary considerably from species to species, and morphological characters in crown shape have been used to identify species. Cusp pattern is one of the characters in crown shape. In the processes governing the formation of cusp pattern, the Shh pathway has been implicated as an important player. Suppression of Shh signaling activity in vitro in explant assays appears to induce supernumerary cusp formation in wild-type tooth germs. However, the in vivo role of Shh signaling in cusp pattern formation and the molecular mechanisms by which Shh regulates cusp patterning are not clear. Here, through in vivo phenotypic analyses of mice in which Shh activity was suppressed and compared with wild-type mice, we characterized differences in the location, number, incidence, and shape of supernumerary cusps in molars at embryonic day 15.5. We found that the distances between cusps were reduced in molars of Shh activity–suppressed mice in vivo. These findings confirm and extend the previous idea that Shh acts as an inhibitor in the reaction-diffusion model for cusp pattern formation by negatively regulating the intercuspal distance. We uncovered a significant reduction of expression level of Sostdc1, which encodes a secreted modulator of Wnt signaling, after suppression of Shh activity. The supernumerary cusp formation in Sostdc1−/− mice and compound Sostdc1 and Lrp mutant mice indicates a strong association between Wnt and Shh signaling pathways in cusp patterning. In further support of this idea, there is a high degree of similarity in the supernumerary cusp patterns of mice lacking Sostdc1 or Shh at embryonic day 15.5. These results suggest that Shh plays an inhibitory role in cusp pattern formation by modulating Wnt signaling through the positive regulation of Sostdc1.

Hedgehog signalling regulates patterning of the murine and human dentitions through Gas1 co-receptor function

“…These defects extended to the dentition where Shh GFP/GFP mice have fusion between M1 and M2 but no supernumerary teeth (Fig. 7A, B) (Cho et al, 2011; Kim et al, 2019). The loss of a single Gas1 allele did not affect the underlying molar phenotype in either a Shh GFP heterozygous or homozygous background (Fig.…”

“…Shh has been shown to restrict cusp formation by regulating the spacing between cusps within individual teeth (Cho et al, 2011; Harjunmaa et al, 2012; Harjunmaa et al, 2014; Kim et al, 2019) and is also required for appropriate spatial patterning between teeth within the molar dentition (Cho et al, 2011). Specifically, a negative feedback reaction-diffusion model has been identified with Wnt signalling activating Shh in the enamel knot; which in turn, activates the Wnt-inhibitor Wise in surrounding mesenchyme (Cho et al, 2011; Kim et al, 2019). The effects of Shh inhibition on cusp patterning have been investigated in embryos following maternal administration of the Shh blocking antibody 5E1.…”

“…The effects of Shh inhibition on cusp patterning have been investigated in embryos following maternal administration of the Shh blocking antibody 5E1. The effects are variable, associated with both shape and locational diversity and influenced by multiple factors, including the timing of activity suppression (Cho et al, 2011; Kim et al, 2019). The maxillary M1 and mandibular M2 are the teeth predominantly affected with supernumerary cusps - located in the M1 mesial anterocone (prestyle), distal hypocone (posterocone) and mesial papracone, and M2 mesial metaconid (lingual anteroconid).…”

“…There may be a number of potential reasons for these variations; not least the fact that in order to study coronal anatomy in erupted teeth the Gas1 −/− mice analysed were those without cleft palate and surviving to adulthood, with a relatively milder craniofacial phenotype (Seppala et al, 2007). Moreover, the most severe molar pattern defects have been reported following pharmacological inhibition of Shh activity in the developing tooth from around E14.5 (Cho et al, 2011; Kim et al, 2019). In Gas1 −/− mice, whilst there is a reduction in Shh signalling within the tooth germ, transduction is not completely lost and therefore phenotypic changes might be expected to be more subtle, particularly within the context of a reaction-diffusion mechanism.…”

Signaling Modulations of miR-206-3p in Tooth Morphogenesis

“…Down-regulation of Axin2 both in the inhibitor and mimic treated specimen suggested that Axin2 functions autonomously in treated tissues not working as a negative feedback regulator of Wnt signaling. Further, the levels of Fgf4 and Shh , two important signaling factors for tooth development [ 46 , 47 ], were altered in the EK and IEE, presumably contributing to the altered morphogenesis of EK and overall tooth structure. These results suggested that miR-206-3p regulated tooth development through the Wnt, Bmp, and Shh signaling pathways.…”