title: Ultrastructural and immunohistochemical analysis of the 8-20 week human fetal pancreas.
abstract: Development of the human pancreas is well-known to involve tightly controlled differentiation of pancreatic precursors to mature cells that express endocrine- or exocrine-specific protein products. However, details of human pancreatic development at the ultrastructural level are limited. The present study analyzed 8-20 week fetal age human pancreata using scanning and transmission electron microscopy (TEM), TEM immunogold and double or triple immunofluorescence staining. Primary organization of islets and acini occurred during the developmental period examined. Differentiating endocrine and exocrine cells developed from the ductal tubules and subsequently formed isolated small clusters. Extracellular matrix fibers and proteins accumulated around newly differentiated cells during their migration and cluster formation. Glycogen expression was robust in ductal cells of the pancreas from 8-15 weeks of fetal age; however, this became markedly reduced at 20 weeks, with a concomitant increase in acinar cell glycogen content. Insulin secretory granules transformed from being dense and round at 8 weeks to distinct geometric (multilobular, crystalline) structures by 14-20 weeks. Initially many of the differentiating endocrine cells were multihormonal and contained polyhormonal granules; by 20 weeks, monohormonal cells were in the majority. Interestingly, certain secretory granules in the early human fetal pancreatic cells showed positivity for both exocrine (amylase) and endocrine proteins. This combined ultrastructural and immunohistochemical study showed that, during early developmental stages, the human pancreas contains differentiating epithelial cells that associate closely with the extracellular matrix, have dynamic glycogen expression patterns and contain polyhormonal as well as mixed endocrine/exocrine granules.
authors.affiliation: a Children's Health Research Institute; Western University ; London , ON , Canada.
authors.forename: Matthew
authors.initials: M
authors.lastname: Riopel
authors.forename: Jinming
authors.initials: J
authors.lastname: Li
authors.forename: George F
authors.initials: GF
authors.lastname: Fellows
authors.forename: Cynthia G
authors.initials: CG
authors.lastname: Goodyer
authors.forename: Rennian
authors.initials: R
authors.lastname: Wang
mesh_terms: D055098:Endocrine Cells / Q000648:ultrastructure; D005455:Fluorescent Antibody Technique; D005865:Gestational Age; D006003:Glycogen / Q000032:analysis; D006801:Humans; D007150:Immunohistochemistry; D007328:Insulin / Q000032:analysis; D008855:Microscopy, Electron, Scanning; D017348:Microscopy, Electron, Scanning Transmission; D010179:Pancreas / Q000737:chemistry / Q000196:embryology* / Q000648:ultrastructure; D022142:Secretory Vesicles / Q000648:ultrastructure
chemical_list: D007328:Insulin; D006003:Glycogen
keywords: CK19, Cytokeratin 19; ECM, extracellular matrix; PDX-1, pancreatic and duodenal homeobox 1; SEM, scanning electron microscopy; TEM, transmission electron microscopy; electron microscopy; glycogen; human fetal pancreas; insulin granules; multihormonal cells; polyhormonal granules