MAPPING THE ORIGIN OF THE AVIAN ENTERIC NERVOUS-SYSTEM WITH A RETROVIRAL MARKER

The enteric nervous system is largely formed from the vagal neural cre st which arises from the neuroaxis between somites 1-7. In order to ev aluate the contribution of different regions of the vagal crest to the enteric nervous system, we marked crest cells by injecting somites 1- 10 with a replication-defective spleen necrosis virus vector which con tains the marker gene lacZ. After incubation in X-gal, lacZ-positive b lue cells were found in the wall of the gut in three locations. Most w ere found at the peripheral edge of the developing circular muscle and within the developing submucosa, sites characteristic of developing g anglia. LacZ-positive cells in these ganglionic sites were always surr ounded by HNK-1 immunostained cells, confirming their neural crest ori gin. LacZ-positive cells were also seen in a third location, the circu lar muscle layer of the esophagus and crop, and were separated from th e HNK-1 positive ganglionic elements. These cells in the circular musc le are probably muscle cells derived from labeled mesodermal cells of the somite. Injection of somites 3, 4, 5, and 6 resulted in the larges t percentage of preparations with lacZ-positive crest-derived cells an d in the largest number of positive cells in the gut. After injection of these somites, lacZ-positive crest-derived cells were found in all regions of the gut from the proventriculus to the rectum. Very few pos itive crest-derived cells were found in the esophagus. Injection of so mites 1, 2, and 7 resulted in a smaller percentage of preparations wit h positive crest-derived cells and in a smaller number of positive cre st-derived cells, which were confined to the fore and midgut. The gizz ard was the gut region most frequently containing labeled cells and th e rectum was the region least frequently containing such cells. This s uggests that the number of crest cells available for colonization of t he gut decreases as the distance from the gizzard increases. We conclu de that the region of the neuroaxis between somites 3-6 is the major s ource of crest cells to the gut and that crest cells from different se gments of the neuroaxis do not appear to be segregated to different re gions of the gut. (C) 1994 Wiley-Liss, Inc.