Can a Non-gut Mesenchyme Support Differentiation of Gut Endocrine Cells?

This experiment was designed to find out if endoderm lacks an intrinsic ability to give rise to gut endocrine cells, and, if not, whether differentiation of endocrine cells can be supported by mesenchyme from a source outside the digestive tract. Heterospecific combinations of proventricular endoderm and flank mesenchyme from chick and quail embryos at 3.25-4 days of incubation were grown as chorio-allantoic grafts to a final incubation age of 21 days. Re-associated proventricular endoderm and mesenchyme served as controls. The proventricular endoderm induced some smooth muscle in the flank mesenchyme but the latter did not support as advanced glandular morphogenesis as did proventricular mesenchyme. Nevertheless, endocrine cells differentiated in experimental as in control grafts and at similar frequencies. The various types were distinguished immunocytochemically by their contained peptides; the range of types found was specific for the proventriculus. Hence it is concluded not only that the particular non-gut mesenchyme used does support differentiation of gut endocrine cells, but also that the determination of the progenitors of endocrine cells, and the selection of the range of types destined to differentiate in a particular part of the digestive tract under normal circumstances, occurs early in development--before 3.25 days of incubation in the case of the proventriculus.