Transcriptional regulation in mesenchymal condensations during formation of the cranium

The vertebrate skull is composed of many skeletal elements originating from cranial neural crest cells (cNCCs). CNCCs arise from the neural plate border, migrate into multiple regions of the developing embryo, and differentiate into various cell types, such as cartilage and bones, peripheral nerves and glia, melanocytes, and connective tissues. The morphogenesis of the craniofacial region encompasses several processes, from epithelial-mesenchymal induction and mesenchymal condensation to endochondral or intramembranous ossification. However, the molecular and genetic pathways regulating cranial cartilage shaping and growth during embryogenesis are poorly understood. The aim of this work was to focus on the development of the mandibular arch, palatal shelves, maxillary prominence (MxP), and hyoid apparatus by utilizing Wnt1-Cre2-induced Meis2 conditional knock-out (cKO) mice. We present a mouse model in which several craniofacial bones are malformed due to improper molecular mechanisms controlling mesenchymal condensations. Meis2 cKO embryos exhibit ectopic loci of mesenchymal condensations and proliferation of cartilage and bone precursors, leading to increased ossification. These processes contribute to the phenotype observed in our model, which displays an aberrant hyoid apparatus, cleft palate,...