Effects of tri-iodothyronine (T3), insulin, insulin-like growth factor I (IGF-I) and transforming growth factor beta1 (TGFbeta1) on the proportion of insulin cells in cultured embryonic chick pancreas.

With a view to ultimately identifying factors involved in the development of pancreatic insulin cells, we have cultured dorsal pancreatic buds from 5-day chick embryos on a basement membrane matrix (Matrigel) in a serum-free medium supplemented with selected factors. The endodermal components of the buds were freed of almost all the mesenchyme so as to eradicate as much as possible of this source of some such factors. In 7-day cultures, insulin and glucagon cells were demonstrated immunocytochemically; numbers of insulin cells were expressed as a percentage of insulin plus glucagon cell counts. Our standard medium contained insulin. Addition of tri-iodothyronine to this medium did not increase the proportion of insulin cells, but in combination with raised concentrations of glucose and essential amino acids it improved somewhat the marked increase previously recorded for these nutrient conditions. Omission of insulin from the standard medium greatly reduced the proportion of these cells; substitution of insulin by insulin-like growth factor I increased the proportion considerably more than did insulin. To test for an overall effect of growth factors, explants were cultured in standard medium on Matrigel containing reduced amounts of growth factors: the proportion of insulin cells proved to be increased over that reached on normal Matrigel. The suspicion that transforming growth factor beta1, a component of Matrigel, might act to reduce the proportion of insulin cells was tested and found to be correct. It is suggested that the different factors studied here may affect either or both of proliferation and determination in the differentiation pathway of insulin vis-à-vis glucagon cells.