Sacral neural crest cells colonise aganglionic hindgut in vivo but fail tocompensate for lack of enteric ganglia

The vagal neural crest is the origin of majority of neurons and glia that c onstitute the enteric nervous system, the intrinsic innervation of the gut. We have recently confirmed that a second region of the neuraxis, the sacra l neural crest, also contributes to the enteric neuronal and glial populati ons of both the myenteric and the submucosal plexuses in the chick, caudal to the level of the umbilicus. Results from this previous study showed that sacral neural crest-derived precursors colonised the gut in significant nu mbers only 4 days after vagal derived cells had completed their migration a long the entire length of the gut. This observation suggested that in order to migrate into the hindgut and differentiate into enteric neurons and gli a, sacral neural crest cells may require an interaction with vagal-derived cells or with factors or signalling molecules released by them or their pro geny. This interdependence may also explain the inability of sacral neural crest cells to compensate for the lack of ganglia in the terminal hindgut o f Hirschsprung's disease in humans or aganglionic megacolon in animals. To investigate the possible interrelationship between sacral and vagal derived neural crest cells within the hindgut, we mapped the contribution of vario us vagal neural crest regions to the gut and then ablated appropriate secti ons of chick vagal neural crest to interrupt the migration of enteric nervo us system precursor cells and thus create an aganglionic hindgut model in v ivo. In these same ablated animals, the sacral level neural axis was remove d and replaced with the equivalent tissue from quail embryos, thus enabling us to document, using cell-specific antibodies, the migration and differen tiation of sacral crest-derived cells. Results showed that the vagal neural crest contributed precursors to the enteric nervous system in a regionalis ed manner. When quail-chick grafts of the neural tube adjacent to somites 1 -2 were performed, neural crest cells were found in enteric ganglia through out the preumbilical gut. These cells were most numerous in the esophagus, sparse in the preumbilical intestine, and absent in the postumbilical gut. When similar grafts adjacent to somites 3-5 or 3-6 were carried out, crest cells were found within enteric ganglia along the entire gut, from the prox imal esophagus to the distal colon. Vagal neural crest grafts adjacent to s omites 6-7 showed that crest cells from this region were distributed along a caudal-rostral gradient, being most numerous in the hindgut, less so in t he intestine, and absent in the proximal foregut. In order to generate aneu ral hindgut in vivo, it was necessary to ablate the vagal neural crest adja cent to somites 3-6, prior to the 13-somite stage of development. When such ablations were performed, the hindgut, and in some cases also the cecal re gion, lacked enteric ganglionated plexuses. Sacral neural crest grafting in these vagal neural crest ablated chicks showed that sacral cells migrated along normal, previously described hindgut pathways and formed isolated gan glia containing neurons and glia at the levels of the presumptive myenteric and submucosal plexuses. Comparison between vagal neural crest-ablated and nonablated control animals demonstrated that sacral-derived cells migrated into the gut and differentiated into neurons in higher numbers in the abla ted animals than in controls. However, the increase in numbers of sacral ne ural crest-derived neurons within the hindgut did not appear to be sufficie ntly high to compensate for the lack of vagal-derived enteric plexuses, as ganglia containing sacral neural crest-derived neurons and glia were small and infrequent. Our findings suggest that the neuronal fate of a relatively fixed subpopula tion of sacral neural crest cells may be predetermined as these cells neith er require the presence of vagal derived enteric precursors in order to col onise the hindgut, nor are capable of dramatically altering their prolifera tion or differentiation. (C) 2000 Academic Press.