Islet Formation during the Neonatal Development in Mice
Figure 4
Islet formation in the neonatal pancreas.
A: Increased ratio of alpha-cells to beta-cells in the neonatal pancreas. The difference was significant at all time points compared to the adult (8-mo) as a control. B: Frequency of alpha-, beta-, and exocrine-cell proliferation. Both alpha- and beta-cell proliferation at P1 was significantly increased compared to P21. C: Endocrine-cells coated with a layer of extracellular matrix (P1). Immunohistochemical staining for Insulin (green), glucagon (red) and collagen IV (yellow) is shown. Note that intra-islet blood vessels are also associated with the extracellular matrix. Scale bar is 50 µm. D: A fission model of islet formation in the neonatal pancreas. a. Endocrine cells proliferate contiguously, forming branching cord-like structures in the fetal and newborn pancreas. b. Islet formation in the neonatal pancreas may occur by fission of elongated structures composed of beta-cells and surrounding alpha-cells. The fission process appears to be random, producing islets of different size. c. Each islet is subsequently coated with a layer of extracellular matrix that stabilizes the structure. This process of islet formation may also result in small isolated clusters of pancreatic endocrine cells that persist even in the adult pancreas. d. Beta-cell mass expansion within an islet leads to an alpha-cell ratio of 5–10%.