Notch Signalling Controls Differential Proliferation During Rotation and Asymmetric Morphogenesis of Mouse Incisors

Rodent incisors exhibit pronounced labial–lingual asymmetry, with enamel deposited exclusively on the labial surface and cementum on the lingual surface. This asymmetry arises early in development as the initially symmetrical dental epithelium rotates and reorients along the jaw axis. Here, we investigated the cellular and molecular mechanisms underlying this process. Quantitative cell-cycle analyses and transcriptomic profiling before and during epithelial rotation revealed accelerated proliferation, shorter cell-cycle duration, and enrichment of DNA replication and mitotic genes within the labial epithelium compared with the lingual epithelium. The evolutionarily conserved Notch signalling pathway, a regulator of cell proliferation and fate, was asymmetrically active during this period, with Notch2 expression restricted to the labial domain. Lineage tracing demonstrated that Notch2-expressing cells and their progeny preferentially contribute to the enamel-producing compartment. Epithelial-specific deletion of Notch2 produced no obvious early morphological phenotype and induced upregulation of other Notch pathway components. By contrast, pharmacological Notch inhibition reduced epithelial asymmetry and altered S-phase progression, and decreased Ccnd1 and Cdk6 expression. Together, these findings implicate Notch signalling in regional cell-cycle dynamics during early mouse incisor asymmetry, while suggesting that other Notch components may compensate for Notch2 loss.