The long-term objective of this work is to define the factors that specify the rostrocaudal axis of the early avian neural crest. Different rostrocaudal populations of premigratory neural crest cells differ in their capacities to form certain cell types. The most thoroughly documented of these differences relates to the chondrogenic potential of the neural crest. Cranial neural crest cells normally give rise to large amounts of cartilage and bone, whereas trunk neural crest cells lack the ability to form cartilage. Rostrocaudal differences in the neurogenic potential of the neural crest have also been identified. Cranial and trunk neural crest cells exhibit different developmental potentials in vitro as well as in vivo. In vitro differences in protein expression by cranial and trunk neural crest cells can be used to assay for factors that may be involved in determining the rostrocaudal axis of the neural crest. The goal of the present work is to identify factors that promote the expression of cranial-specific phenotypes by premigratory neural crest cells in vitro.
The specific aims of the proposed studies are to: (1) Characterize markers that are expressed by cranial neural crest cells in vitro, but not by trunk neural crest cells. Three such markers are currently available: fibronectin (FN), procollagen I (Col I) and neurofilament (NF). FN-, Col I-, and NF- immunoreactive cells all are abundant in cranial neural crest cultures, but rare in trunk neural crest cultures. The developmental appearance of these markers in cranial cultures will be quantified in more detail, as will the differences in expression of these markers in cranial and trunk cultures. (2) Use these markers to examine the early tissue interactions that specify the cranial region of the neural crest. The hypothesis to be tested is that the expression of cranial-specific phenotypes by premigratory neural crest cells requires an interaction with anterior mesoderm. Coculture experiments will be used to determine if anterior mesoderm contains factors that can induce trunk neural crest cells to express cranial-specific traits in vitro, and to produce cartilage in vivo. (3) Examine the possibility that transforming growth factors (TGF's) mediate the induction of cranial neural crest-specific traits. Preliminary evidence indicates that TGFbeta-1 stimulates trunk neural crest cells in vitro to express at least one cranial-specific phenotype, FN immunoreactivity. The ability of TGF-beta1 and related growth factors to induce the expression of other cranial-specific traits in trunk neural crest cells will be explored. Cranial neural crest cells give rise to most of the cartilage and bone of the facial skeleton. By defining the developmental mechanisms that endow cranial neural crest cells with the ability to form cartilage, the proposed studies may provide insight into the etiology of craniofacial malformations.
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