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The identification of critical time windows of postnatal root elongation in response to Wnt/β-catenin signaling.

OBJECTIVES
In this study, we attempted to define the precise window of time for molar root elongation using a gain-of-function mutation of β-catenin model.


MATERIALS AND METHODS
Both the control and constitutively activated β-catenin (CA-β-cat) mice received a one-time tamoxifen administration (for activation of β-catenin at newborn, postnatal day-3, or -5, or -7, or -9), and were harvested at the same stage of P21. Multiple approaches were used to define the window of time of postnatal tooth root formation.


RESULTS
In the early activation groups (tamoxifen induction at newborn, or P3 or P5) there was a lack of molar root elongation in the CA-β-cat mice. When induced at P7, the root length was slightly reduced at P21. However, the root length was essentially the same as that in the control when β-cat activated at P9. This study indicates that root elongation occurs in a narrow time of window, which is highly sensitive to a change of β-catenin levels. Molecular studies showed a drastic decrease in the levels of nuclear factor I-C (NFIC) and osterix (OSX), plus sharp reductions of odontoblast differentiation markers, including Nestin, dentin sialoprotein (DSP) and dentin matrix protein 1 (DMP1) at both mRNA and protein levels.


CONCLUSIONS
Murine molar root elongation is precisely regulated by the Wnt/β-catenin signaling within a narrow window of time (newborn to day 5).