Control of cranial ectomesenchyme fate by Nr2f nuclear receptors.

Certain cranial neural crest cells are uniquely endowed with the ability to make skeletal cell types otherwise only derived from mesoderm. As these cells migrate into the pharyngeal arches, they downregulate neural crest specifier genes and upregulate so-called ectomesenchyme genes that are characteristic of skeletal progenitors. Although both external and intrinsic factors have been proposed as triggers of this transition, the details remain obscure.

Patterning of cartilaginous condensations in the developing facial skeleton.

Adult endochondral bones are prefigured in the embryo as cellular condensations within fields of more loosely distributed skeletal progenitors. How these early condensations are initiated and shaped has remained enigmatic, despite the wealth of research on later stages of cartilage differentiation and endochondral ossification. Using the simple larval zebrafish facial skeleton as a model, we reevaluate the involvement of the master cartilage regulator Sox9 in shaping facial condensations and find it to be largely dispensable.