title: Independent development of pancreatic alpha- and beta-cells from neurogenin3-expressing precursors: a role for the notch pathway in repression of premature differentiation.
abstract: The nature and identity of the pancreatic beta-cell precursor has remained elusive for many years. One model envisions an early multihormonal precursor that gives rise to both alpha- and beta-cells and the other endocrine cell types. Alternatively, beta-cells have been suggested to arise late, directly from the GLUT2- and pancreatic duodenal homeobox factor-1 (PDX1)-expressing epithelium, which gives rise also to the acinar cells during this stage. In this study, we have identified a subset of the PDX1+ epithelial cells that are marked by expression of Neurogenin3 (Ngn3). Ngn3, a member of the basic helix-loop-helix (bHLH) family of transcription factors, is suggested to act upstream of NeuroD in a bHLH cascade. Detailed analysis of Ngn3/paired box factor 6 (PAX6) and NeuroD/PAX6 co-expression shows that the two bHLH factors are expressed in a largely nonoverlapping set of cells, but such analysis also suggests that the NeuroD+ cells arise from cells expressing Ngn3 transiently. NeuroD+ cells do not express Ki-67, a marker of proliferating cells, which shows that these cells are postmitotic. In contrast, Ki-67 is readily detected in Ngn3+ cells. Thus, Ngn3+ cells fulfill the criteria for an endocrine precursor cell. These expression patterns support the notion that both alpha- and beta-cells develop independently from PDX1+/Ngn3+ epithelial cells, rather than from GLU+/INS+ intermediate stages. The earliest sign of alpha-cell development appears to be Brain4 expression, which apparently precedes Islet-1 (ISL1) expression. Based on our expression analysis, we propose a temporal sequence of gene activation and inactivation for developing alpha- and beta-cells beginning with activation of NeuroD expression. Endocrine cells leave the cell cycle before NeuroD activation, but re-enter the cell cycle at perinatal stages. Dynamic expression of Notch1 in PDX+ epithelial cells suggests that Notch signaling could inhibit a Ngn-NeuroD cascade as seen in the nervous system and thus prevent premature differentiation of endocrine cells.
authors.affiliation: Department of Developmental Biology, Hagedorn Research Institute, Gentofte, Denmark.
authors.forename: J
authors.initials: J
authors.lastname: Jensen
authors.forename: R S
authors.initials: RS
authors.lastname: Heller
authors.forename: T
authors.initials: T
authors.lastname: Funder-Nielsen
authors.forename: E E
authors.initials: EE
authors.lastname: Pedersen
authors.forename: C
authors.initials: C
authors.lastname: Lindsell
authors.forename: G
authors.initials: G
authors.lastname: Weinmaster
authors.forename: O D
authors.initials: OD
authors.lastname: Madsen
authors.forename: P
authors.initials: P
authors.lastname: Serup
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D015415:Biomarkers; D002454:Cell Differentiation / Q000502:physiology; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D005934:Glucagon / Q000378:metabolism; D018398:Homeodomain Proteins; D007515:Islets of Langerhans / Q000166:cytology*; D019394:Ki-67 Antigen / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism / Q000502:physiology; D051379:Mice; D008815:Mice, Inbred Strains; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D010179:Pancreas / Q000196:embryology / Q000378:metabolism; D051381:Rats; D011920:Rats, Inbred WF; D051881:Receptor, Notch1; D051883:Receptor, Notch2; D011956:Receptors, Cell Surface / Q000378:metabolism; D051880:Receptors, Notch; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D015415:Biomarkers; D005934:Glucagon; D018398:Homeodomain Proteins; D019394:Ki-67 Antigen; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D051881:Receptor, Notch1; D051883:Receptor, Notch2; D011956:Receptors, Cell Surface; D051880:Receptors, Notch; D015534:Trans-Activators; D014157:Transcription Factors; C407737:Neurog3 protein, mouse; C498696:Neurog3 protein, rat; C497762:Notch1 protein, mouse; C497763:Notch1 protein, rat; C497765:Notch2 protein, mouse; C497766:Notch2 protein, rat; C084010:pancreatic and duodenal homeobox 1 protein; C093564:Neurogenic differentiation factor 1