Colonization of the post-umbilical bowel by cells derived from the sacral neural crest: direct tracing of cell migration using an intercalating probe and a replication-deficient retrovirus

Experiments were done to test the hypothesis that the avian gut is colonized by cells derived from both vagal and sacral regions of the neural crest. A fluorescent dye, diI (1,1-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate), and a replication-deficient retrovirus (LZ10; Galileo et al. 1990) were employed as tracers. Since LZ10 was constructed with lacZ of E. coli as a reporter gene, infected cells were identified by demonstrating beta-galactosidase immunoreactivity. DiI and LZ10 were injected between the neural tube and surface ectoderm (before the migration of crest cells away from the injection sites) at vagal, truncal (diI only), or sacral axial levels. The bowel was examined 4 days later in order to allow crest-derived cells sufficient time to migrate to the gut. Following injections of either tracer into the vagal crest, labelled cells were found in the gizzard and duodenum. When diI or LZ10 was injected into the sacral crest, labelled cells were seen in the post-umbilical bowel and ganglion of Remak. In the hindgut, marked cells were concentrated in the mesenchyme, just internal to the serosa, and were never observed rostral to the umbilicus. No fluorescent cells were ever found in the bowel following truncal injections of diI, although such cells were observed in sympathetic ganglia. Labelled cells were always found in dorsal root ganglia, no matter which tracer or level of the crest was injected. In embryos injected with LZ10, infected cells in the gut and dorsal root ganglia displayed a neural crest marker (NC-1 immunoreactivity). These observations confirm that the gut is colonized by cells from the sacral as well as the vagal region of the neural crest and that the emigres from the sacral crest are confined to the post-umbilical bowel.