Intestinal mesenchyme provokes differentiation of intestinal endocrine cells in gizzard endoderm

The gizzard (muscular stomach) of chicks is deficient in endocrine cells at hatching. It has previously been shown that proventricular types and proportions of endocrine cells can be induced in gizzard endoderm under the influence of proventricular (glandular stomach) mesenchyme. In order to test its capacity to form nongastric endocrine cell types, gizzard endoderm of 3.75- to 5-day chick embryos was combined with mesenchyme from the small intestine of 3.5- to 4-day quail embryos. The combinations were grown as chorio-allantoic grafts until they attained an incubation age comparable to that of hatching chicks. Controls comprised reassociated endoderm and mesenchyme of chick gizzard and of quail intestine. In the experimental grafts, morphogenesis was predominantly intestinal but some grafts showed gizzard-like features, particularly if the endoderm had been provided by older donors. All intestinal endocrine cell types, including those also found in the normal proventriculus (serotonin-, glucagon-, pancreatic polypeptide-, neurotensin- and somatostatin-immunoreactive cells) differentiated in experimental grafts, some even where morphogenesis was gizzard-like. Hence progenitors of not only gastric, but also intestinal, endocrine cells are indeed present in gizzard endoderm. The possibility that gizzard mesenchyme is inhibitory to endocrine cell differentiation is mooted. Motilin- and secretin-immunoreactive cells, which are characteristic of the intestine but not of the proventriculus of chicks at hatching, were respectively sparse or absent when the endoderm was derived from older donors. Thus the ability of gizzard endoderm to differentiate into nongastric endocrine cell types declines before its capacity to form gastric types. The unexpected appearance of gastrin-releasing peptide (GRP)-immunoreactive cells, a proventricular type not found in normal chick intestine, suggests that the intestinal mesenchyme, at least in this instance, was exercising a permissive role.