biostudies-literatureLee JMNational Center for Advancing Translational SciencesNIDCR NIH HHSNCATS NIH HHSNational Institute of Dental and Craniofacial Research832-839https://www.ebi.ac.uk/biostudies/studies/S-EPMC9218501biostudies-literatureUnknown101(7)Tooth agenesis is a common structural birth defect in humans that results from failure of morphogenesis during early tooth development. The homeobox transcription factor Msx1 and the canonical Wnt signaling pathway are essential for "bud to cap" morphogenesis and are causal factors for tooth agenesis. Our recent study suggested that Msx1 regulates Wnt signaling during early tooth development by suppressing the expression of <i>Dkk2</i> and <i>Sfrp2</i> in the tooth bud mesenchyme, and it demonstrated partial rescue of <i>Msx1</i>-deficient molar teeth by a combination of DKK inhibition and genetic inactivation of SFRPs. In this study, we found that Sostdc1/Wise, another secreted Wnt antagonist, is involved in regulating the odontogenic pathway downstream of Msx1. Whereas <i>Sostdc1</i> expression in the developing tooth germ was not increased in <i>Msx1</i>^-/- embryos, genetic inactivation of <i>Sostdc1</i> rescued maxillary molar, but not mandibular molar, morphogenesis in <i>Msx1</i>^-/- mice with full penetrance. Since the <i>Msx1</i>^-/-;<i>Sostdc1</i>^-/- embryos exhibited ectopic <i>Dkk2</i> expression in the developing dental mesenchyme, similar to <i>Msx1</i>^-/- embryos, we generated and analyzed tooth development in <i>Msx1</i>^-/-;<i>Dkk2</i>^-/- double and <i>Msx1</i>^-/-;<i>Dkk2</i>^-/-;<i>Sostdc1</i>^-/- triple mutant mice. The <i>Msx1</i>^-/-;<i>Dkk2</i>^-/- double mutants showed rescued maxillary molar morphogenesis at high penetrance, with a small percentage also exhibiting mandibular molars that transitioned to the cap stage. Furthermore, tooth development was rescued in the maxillary and mandibular molars, with full penetrance, in the <i>Msx1</i>^-/-;<i>Dkk2</i>^-/-;<i>Sostdc1</i>^-/- mice. Together, these data reveal 1) that a key role of Msx1 in driving tooth development through the bud-to-cap transition is to control the expression of <i>Dkk2</i> and 2) that modulation of Wnt signaling activity by Dkk2 and Sostdc1 plays a crucial role in the Msx1-dependent odontogenic pathway during early tooth morphogenesis.Journal of dental researchMSX1 Drives Tooth Morphogenesis Through Controlling Wnt Signaling Activity.PMC9218501R01DE018401R01DE0270462T32DE023526R01 DE018401R03 DE030985T32 DE023526UL1 TR0014121R03DE0309855KL2TR0013-05R01 DE027046Kwon HEJiang RLee JMChai OHLan YQin CfalseMSX1 Drives Tooth Morphogenesis Through Controlling Wnt Signaling Activity.Tooth agenesis is a common structural birth defect in humans that results from failure of morphogenesis during early tooth development. The homeobox transcription factor Msx1 and the canonical Wnt signaling pathway are essential for "bud to cap" morphogenesis and are causal factors for tooth agenesis. Our recent study suggested that Msx1 regulates Wnt signaling during early tooth development by suppressing the expression of <i>Dkk2</i> and <i>Sfrp2</i> in the tooth bud mesenchyme, and it demonstrated partial rescue of <i>Msx1</i>-deficient molar teeth by a combination of DKK inhibition and genetic inactivation of SFRPs. In this study, we found that Sostdc1/Wise, another secreted Wnt antagonist, is involved in regulating the odontogenic pathway downstream of Msx1. Whereas <i>Sostdc1</i> expression in the developing tooth germ was not increased in <i>Msx1</i>^-/- embryos, genetic inactivation of <i>Sostdc1</i> rescued maxillary molar, but not mandibular molar, morphogenesis in <i>Msx1</i>^-/- mice with full penetrance. Since the <i>Msx1</i>^-/-;<i>Sostdc1</i>^-/- embryos exhibited ectopic <i>Dkk2</i> expression in the developing dental mesenchyme, similar to <i>Msx1</i>^-/- embryos, we generated and analyzed tooth development in <i>Msx1</i>^-/-;<i>Dkk2</i>^-/- double and <i>Msx1</i>^-/-;<i>Dkk2</i>^-/-;<i>Sostdc1</i>^-/- triple mutant mice. The <i>Msx1</i>^-/-;<i>Dkk2</i>^-/- double mutants showed rescued maxillary molar morphogenesis at high penetrance, with a small percentage also exhibiting mandibular molars that transitioned to the cap stage. Furthermore, tooth development was rescued in the maxillary and mandibular molars, with full penetrance, in the <i>Msx1</i>^-/-;<i>Dkk2</i>^-/-;<i>Sostdc1</i>^-/- mice. Together, these data reveal 1) that a key role of Msx1 in driving tooth development through the bud-to-cap transition is to control the expression of <i>Dkk2</i> and 2) that modulation of Wnt signaling activity by Dkk2 and Sostdc1 plays a crucial role in the Msx1-dependent odontogenic pathway during early tooth morphogenesis.2022-01-01T00:00:00Z2022 Jul2024-11-11T22:34:12.63Z2024-11-11T22:34:12.63ZS-EPMC92185013511485210.1177/00220345211070583