Inhibition of Wnt signaling by Wise (Sostdc1) and negative feedback from Shh controls tooth number and patterning
ABSTRACT Mice carrying mutations in Wise (Sostdc1) display defects in many aspects of tooth development, including tooth number, size and cusp pattern. To understand the basis of these defects, we have investigated the pathways modulated by Wise in tooth development. We present evidence that, in tooth development, Wise suppresses survival of the diastema or incisor vestigial buds by serving as an inhibitor of Lrp5- and Lrp6-dependent Wnt signaling. Reducing the dosage of the Wnt co-receptor genes Lrp5 and Lrp6 rescues the Wise-null tooth phenotypes. Inactivation of Wise leads to elevated Wnt signaling and, as a consequence, vestigial tooth buds in the normally toothless diastema region display increased proliferation and continuous development to form supernumerary teeth. Conversely, gain-of-function studies show that ectopic Wise reduces Wnt signaling and tooth number. Our analyses demonstrate that the Fgf and Shh pathways are major downstream targets of Wise-regulated Wnt signaling. Furthermore, our experiments revealed that Shh acts as a negative-feedback regulator of Wnt signaling and thus determines the fate of the vestigial buds and later tooth patterning. These data provide insight into the mechanisms that control Wnt signaling in tooth development and into how crosstalk among signaling pathways controls tooth number and morphogenesis.
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ABSTRACT: The mouse embryonic mandible comprises two types of tooth primordia in the cheek region: progressive tooth primordia of prospective functional teeth and rudimentary tooth primordia in premolar region - MS and R2. Mice lacking Sprouty genes develop supernumerary tooth in front of the lower M1 (first molar) primordium during embryogenesis. We focused on temporal-spatial dynamics of Sonic Hedgehog expression as a marker of early odontogenesis during supernumerary tooth development. Using mouse embryos with different dosages of Spry2 and Spry4 genes, we showed that during the normal development of M1 in the mandible the earlier appearing Shh signaling domain of the R2 bud transiently coexisted with the later appearing Shh expression domain in the early M1 primordium. Both domains subsequently fused together to form the typical signaling center representing primary enamel knot (pEK) of M1 germ at embryonic day (E) 14.5. However, in embryos with lower Spry2;Spry4 gene dosages, we observed a non-fusion of original R2 and M1 Shh signaling domains with consequent formation of a supernumerary tooth primordium from the isolated R2 bud. Our results bring new insight to the development of the first lower molar of mouse embryos and define simple tooth unit capable of individual development, as well as determine its influence on normal and abnormal development of the tooth row which reflect evolutionarily conserved tooth pattern. Our findings contribute significantly to existing knowledge about supernumerary tooth formation.BMC Developmental Biology 04/2015; 15(1):21. DOI:10.1186/s12861-015-0070-0 · 2.75 Impact Factor
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ABSTRACT: Bone morphogenetic proteins (BMPs) are antagonized through the action of numerous extracellular protein antagonists, including members from the differential screening-selected gene aberrative in neuroblastoma (DAN) family. In vivo, misregulation of the balance between BMP signaling and DAN inhibition can lead to numerous disease states, including cancer, kidney nephropathy, and pulmonary arterial hypertension. Despite this importance, very little information is available describing how DAN family proteins effectively inhibit BMP ligands. Furthermore, our understanding for how differences in individual DAN family members arise, including affinity and specificity, remains underdeveloped. Here, we present the structure of the founding member of the DAN family, neuroblastoma suppressor of tumorigenicity 1 (NBL1). Comparing NBL1 to the structure of protein related to Dan and Cerberus (PRDC), a more potent BMP antagonist within the DAN family, a number of differences were identified. Through a mutagenesis-based approach, we were able to correlate the BMP binding epitope in NBL1 with that in PRDC, where introduction of specific PRDC amino acids in NBL1 (A58F and S67Y) correlated with a gain-of-function inhibition towards BMP2 and BMP7, but not GDF5. While NBL1S67Y was able to antagonize BMP7 as effectively as PRDC, NBL1S67Y was still 40-fold weaker than PRDC against BMP2. Taken together, this data suggests that alterations in the BMP binding epitope can partially account for differences in the potency of BMP inhibition within the DAN family. Copyright © 2015, The American Society for Biochemistry and Molecular Biology.Journal of Biological Chemistry 01/2015; DOI:10.1074/jbc.M114.628412 · 4.60 Impact Factor
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ABSTRACT: In this study using genetic approaches in mouse we demonstrate that the secreted protein Wise plays essential roles in regulating early bone formation through its ability to modulate Wnt signaling via interactions with the Lrp5 co-receptor. In Wise-/- mutant mice we find an increase in the rate of osteoblast proliferation and a transient increase in bone mineral density. This change in proliferation is dependent upon Lrp5, as Wise;Lrp5 double mutants have normal bone mass. This suggests that Wise serves as a negative modulator of Wnt signaling in active osteoblasts. Wise and the closely related protein Sclerostin (Sost) are expressed in osteoblast cells during temporally distinct early and late phases in a manner consistent with the temporal onset of their respective increased bone density phenotypes. These data suggest that Wise and Sost may have common roles in regulating bone development through their ability to control the balance of Wnt signaling. We find that Wise is also required to potentiate proliferation in chondrocytes, serving as a potential positive modulator of Wnt activity. Our analyses demonstrate that Wise plays a key role in processes that control the number of osteoblasts and chondrocytes during bone homeostasis and provide important insight into mechanisms regulating the Wnt pathway during skeletal development.PLoS ONE 05/2014; 9(5):e96257. DOI:10.1371/journal.pone.0096257 · 3.53 Impact Factor