Strategy for a Biomimetic Paradigm in Dental and Craniofacial Tissue Engineering - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 125

the neural tube, neural crest cells undergo well-orchestrated directed
migration along specifi c pathways to their precise fi nal destinations. The
majority of cranial neural crest cells that are derived from the hindbrain
migrate ventrolaterally from the neural tube in three distinct sub-ecto-
dermal streams adjacent to the even-numbered rhombomeres (rhombo-
mere-2, 4 & 6). In keeping with their craino-caudal axial origins, the three
streams of neural crest cells precisely populate the fi rst, second and third
pharyngeal arches, respectively [44].
During migration, neural crest cells are exposed to a wide variety of
signals controlling their polarity, directionality and possibly their com-
mitment. Surprisingly, when the fi rst arch (mandibular) neural crest cells
were grafted posteriorly in place of second (hyoid) or third (visceral)
arch, the transplanted neural crest cells formed duplicate fi rst arch skel-
etal and muscular elements [45]. These observations led to the proposal of
the neural crest pre-programming model [46]. Upon reaching their fi nal
destinations, neural crest cells proliferate and eventually differentiate into
defi nite cell types, though multi-potent neural crest stem cells with high
plasticity continue to exist and preferentially localize in a niche-like struc-
ture in various types of tissues [47].
When the human embryo is about 3.5 weeks old (3 mm CR stage) the
primitive oro-nasal cavity is a narrow slit-like space lined by ectoderm,
bounded above by the under surface of the brain capsule and below by the
upper surface of the developing heart (Figure 6.5). This close approxima-
tion to the developing nervous and cardiovascular system ensures close
integration and coordination.
Figure 6.5 Histological para-sagittal section of developing mouse head 13 days
pre-natal showing primitive stomatodeum between the developing brain above
and the developing heart below. Inset shows the section of the entire embryo
at lower magnifi cation. (B), developing brain; (Ta) tail; (N), nasal cavity; (T),
developing tongue (Th), thyroid; (H), developing heart; (M), mandibular arch.