Reassessing the embryonic origin and potential of craniofacial ectomesenchyme.

Of all the cell types arising from the neural crest, ectomesenchyme is likely the most unusual. In contrast to the neuroglial cells generated by neural crest throughout the embryo, consistent with its ectodermal origin, cranial neural crest-derived cells (CNCCs) generate many connective tissue and skeletal cell types in common with mesoderm. Whether this ectoderm-derived mesenchyme (ectomesenchyme) potential reflects a distinct developmental origin from other CNCC lineages, and/or epigenetic reprogramming of the ectoderm, remains debated. Whereas decades of lineage tracing studies have defined the potential of CNCC ectomesenchyme, these are being revisited by modern genetic techniques. Recent work is also shedding light on the extent to which intrinsic and extrinsic cues determine ectomesenchyme potential, and whether maintenance or reacquisition of CNCC multipotency influences craniofacial repair. • Cranial neural crest provides a vertebrate-specific source of head mesenchyme. • Epigenetic reprogramming facilitates mesenchyme potential of neural crest. • Region- and species-specific contributions of ectomesenchyme to diverse cell types. • Plasticity of neural crest and mesoderm to contribute to craniofacial mesenchyme. • Unclear potential of cranial neural crest cells for enhanced skeletal repair. [ABSTRACT FROM AUTHOR]