Cranial neural crest cells to mesenchymal progenitors forming the mesenchymal derivatives of head and face
Neural crest cells detach from neural tube one day before dorsalmedial organoizer formation (also the invagination)
A unique feature of vertebrate neurulation is the delamination of neural crest progenitors from the dorsal neuroepithelium before and during neural tube formation.
In mice, rostral neural crest cells detach from the closing neural tube by embryonic day (E)9.0, one day before the dorsomedial telencephalon invaginates to form the bilateral telencephalic vesicles, the prospective cerebral cortical hemispheres.
At E10.5, regional specification of the dorsomedial forebrain neuroepithelium divides areas of the hippocampus, the cortical hem, and the non-neural secretory choroid plexus, which extends into the lateral ventricle. The secreted signaling factor Wnt3a is first expressed by the cortical hem at E10.5 in concordance with the invagination of the dorsal telencephalon.
WNT deletion of mensenchym cells has both craniofacial and neocortex defection
Emx1-Cre-dependent deletion of ß-catenin mice survive to adulthood without apparent neural crest defects while displaying diminished dorsomedial forebrain structures. The dorsomedial structures properly invaginate forming bifurcated lateral ventricles. Contrastingly, Foxg1-Cre-mediated deletion of ß-catenin in both dorsal neuroepithelial and mesenchymal cells, results in severe loss of midline telencephalic structures, failure of midline invagination and associated craniofacial defects , [15]. The marked difference in phenotypic alterations in these two mutant lines may stem from the loss of ß-catenin signaling in mesenchymal cells in Foxg1-Cre;ß-catenin mutants.
Mensenchye cells form cranial skeleton, meninges and pericyte / smooth muscle cells
Elements of the cranial skeleton such as the frontal bone develop by intramembraneous osteogenic condensation of mesenchymal cells derived from neural crest cells, which also contribute substantially to the meninges that cover the telencephalon. In addition, neural crest cells produce non-neural cell types within the brain such as perivascular smooth muscle cells and pericytes
Marker for those mesenchyme cells
A) Staining of Pdgfrß+ neural crest-derived mesenchymal cells from E10 to E14. Dashed lines highlight the dorsomedial mesenchymal cells, which expand at E10 and spread laterally at later ages. At E14, perivascular cells strongly express Pdgfrß. B) A diagram showing mesenchymal cells at the level of dorsoventral axis in the forebrain; the dorsal (Md), lateral (Ml), and ventral (Mv) mesenchymal cells. The derivatives of the neural crest cells are listed with markers used in this study. Ep = epidermis, Ch = cortical hem, Cp = choroid plexus, P = pericytes, m = meninges.
Wnt play role in transition from neural crest cell into mesenchymal progenitor cells
We hypothesized that Wnts secreted from the cortical hem act as a proliferative signal on neural crest derived mesenchymal progenitor cells, which induces their expansion adjacent to the dorsomedial telencephalon and that this initial expansion of mesenchymal progenitor cells contributes to neural crest derived craniofacial structures and proper development of the forebrain.
