Analysis of hindbrain neural crest migration in the long-tailed monkey (Macaca fascicularis)

Neural crest cells make a substantial contribution to normal craniofacial development. Despite advances made in identifying migrating neural crest cells in avian embryos and, more recently, rodent embryos, knowledge of crest cell migration in primates has been limited to what was obtained by conventional morphological techniques. In order to determine the degree to which the nonhuman primate fits the mammalian pattern, we studied the features of putative neural crest cell migration in the hindbrain of the long-tailed monkey (Macaca fascicularis) embryo. Cranial crest cells were identified on the basis of reported distributional and morphological criteria as well as by immunocytochemical detection of the neural cell adhesion molecule (N-CAM) that labels a subpopulation of these cells. The persistent labeling of a sufficient number of crest cells with antibodies to N-CAM following their exit from the rostral, pre-otic and post-otic regions of the hindbrain facilitated tracking them along subectodermal pathways to their respective destinations in the first, second and third pharyngeal arches. Peroxidase immunocytochemistry was also employed to localize laminin and collagen-IV in neuroepithelial basement membranes. At stage 10 (8-11 somites), crest emigration occurred in areas of unfused neural folds through focal disruptions in the neuroepithelial basement membrane in both the rostral and pre-otic regions, although there was little evidence of crest migration in the post-otic hindbrain. By stage 11 (16-17 somites), the neural folds were fused (pre- and post-otic hindbrain) or in the process of fusing (rostral hindbrain), yet crest cell emigration was apparent in all three areas through discontinuities in the basement membrane. Emigration was essentially complete at stage 12 (21 somites) as indicated by nearly continuous cranial neural tube basement membranes. At this stage the pre-ganglia (trigeminal, facioacoustic and glossopharyngeal) were consistently stained with N-CAM. The current study has provided new information on mammalian neural crest in a well-established experimental model for normal and abnormal human development, including its use as a model for the retinoic acid syndrome. In this regard, the current results provide the basis for probing the mechanisms of retinoid embryopathy which may involve perturbation of hindbrain neural crest development.