Pancreas is a combined endocrine and exocrine gland that ...

Pancreas is a combined endocrine and exocrine gland that develops from an outgrowth of the primitive foregut and is closely associated with the upper duodenum. During development,cells of exocrine and endocrine pancreas are both derived from the pancreatic duct epithelium. The endocrine pancreas is composed of the islets of Langerhans that are build of several endocrine cell type: alpha cells (secrete glucagon), beta cells (secrete insulin and amylin), gamma cells (also known as PP or F cells, secrete pancreatic polypeptide), delta cells (secrete somatostatin), and epsilon cells (secrete ghrelin). Alpha, beta and delta cells are the most numerous. In humans, the islet of Langehrans possess the so-called double basement membrane, as both islet cells and islet blood vessels have basal lamina. The endocrine pancreas comprises less than 5% of the pancreas mass, with islets of Langerhans disperesed within the exocrine pancreas tissue. For overview, please refer to Liggitt and Dintzis; "Pancreas"; Comparative Anatomy and Histology; a Mouse, Rat, and Human Atlas; edited by Treuting, Dintzis, and Montine, Elsevier Inc., 2018, 241-250. For review, please refer to Tritschler et al. 2017.

Single cell analysis of bipotent pancreatic progenitors derived from human embryonic stem cells reveals that cell confinement is a prerequisite for endocrine specification (Mamidi et al. 2018). Trunk pancreatic progenitors give rise to ductal and endocrine lineages (ref). Single cell analysis shows that spreading, with the associated extracellular matrix (ECM)-integrin alpha 5 (ITGA5) signaling, drives trunk progenitors towards the ductal fate, while confinment, which disrupts ECM-ITGA5 signaling, drives them towards the endocrine fate (Mamidi et al. 2018).

Neurogenin-3 (NGN3) is the essential pro-endocrine transcription factor, that promotes endocrine specification of trunk progenitors (ref).