EFFECTS OF TRIIODOTHYRONINE (T3), INSULIN, INSULIN-LIKE-GROWTH-FACTOR-I (IGF-I) AND TRANSFORMING-GROWTH-FACTOR-BETA1 (TGF-BETA-1) ON THE PROPORTION OF INSULIN CELLS IN CULTURED EMBRYONIC CHICK PANCREAS

With a view to ultimately identifying factors involved in the developm ent of pancreatic insulin cells, we have cultured dorsal pancreatic bu ds from 5-day chick embryos on a basement membrane matrix (Matrigel) i n a serum-free medium supplemented with selected factors. The endoderm al components of the buds were freed of almost all the mesenchyme so a s to eradicate as much as possible of this source of some such factors . In 7-day cultures, insulin and glucagon cells were demonstrated immu nocytochemically; numbers of insulin cells were expressed as a percent age of insulin plus glucagon cell counts. Our standard medium containe d insulin. Addition of tri-iodothyronine to this medium did not increa se the proportion of insulin cells, but in combination with raised con centrations 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 prop ortion 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 culture d in standard medium on Matrigel containing reduced amounts of growth factors: the proportion of insulin cells proved to be increased over t hat reached on normal Matrigel. The suspicion that transforming growth factor pi, a component of Matrigel, might act to reduce the proportio n 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 insu lin vis-a-vis glucagon cells.