Msx1, belonging to the muscle segment homeobox gene family, is a transcription factor crucial for multiple epithelial-mesenchymal interactions during vertebrate embryogenesis [2,3]. It plays pleiotropic roles in various tissues, regulating cellular proliferation, differentiation, and cell death. Msx1 is associated with pathways like the canonical Wnt signaling pathway, which is essential for certain developmental processes [1].

In tooth development, Msx1 -/- mice have revealed its key role in the "bud to cap" morphogenesis. Msx1 drives tooth development by controlling the expression of Wnt antagonists such as Dkk2 and Sostdc1. Genetic inactivation of Sostdc1 rescued maxillary molar morphogenesis in Msx1 -/- mice, and combined inactivation of Dkk2 and Sostdc1 rescued both maxillary and mandibular molar development in Msx1 -/-;Dkk2 -/-;Sostdc1 -/- mice [1]. In mandibular development, Msx1 -/- mice showed unfused and bifurcated rostral tips of the mandibular processes, along with reduced cell proliferation and down-regulated Bmp signaling, indicating its essentiality for proper mandibular tip formation [4].

In conclusion, Msx1 is essential for tooth and mandibular development as demonstrated by gene-knockout mouse models. These models have provided insights into the role of Msx1 in these processes, which could be relevant for understanding and potentially treating related congenital defects such as tooth agenesis and mandibular clefting.