title: Nkx2.2-repressor activity is sufficient to specify alpha-cells and a small number of beta-cells in the pancreatic islet.
abstract: The homeodomain protein Nkx2.2 (Nkx2-2) is a key regulator of pancreatic islet cell specification in mice; Nkx2.2 is essential for the differentiation of all insulin-producing beta-cells and of the majority of glucagon-producing alpha-cells, and, in its absence, these cell types are converted to a ghrelin cell fate. To understand the molecular functions of Nkx2.2 that regulate these early cell-fate decisions during pancreatic islet development, we created Nkx2.2-dominant-derivative transgenic mice. In the absence of endogenous Nkx2.2, the Nkx2.2-Engrailed-repressor derivative is sufficient to fully rescue glucagon-producing alpha-cells and to partially rescue insulin-producing beta-cells. Interestingly, the insulin-positive cells that do form in the rescued mice do not express the mature beta-cell markers MafA or Glut2 (Slc2a2), suggesting that additional activator functions of Nkx2.2 are required for beta-cell maturation. To explore the mechanism by which Nkx2.2 functions as a repressor in the islet, we assessed the pancreatic expression of the Groucho co-repressors, Grg1, Grg2, Grg3 and Grg4 (Tle1-Tle4), which have been shown to interact with and modulate Nkx2.2 function. We determined that Grg3 is highly expressed in the embryonic pancreas in a pattern similar to Nkx2.2. Furthermore, we show that Grg3 physically interacts with Nkx2.2 through its TN domain. These studies suggest that Nkx2.2 functions predominantly as a transcriptional repressor during specification of endocrine cell types in the pancreas.
authors.affiliation: Program in Molecular Biology, University of Colorado at Denver Health Sciences Center, Aurora, CO 80045, USA.
authors.forename: Michelle J
authors.initials: MJ
authors.lastname: Doyle
authors.forename: Zoe L
authors.initials: ZL
authors.lastname: Loomis
authors.forename: Lori
authors.initials: L
authors.lastname: Sussel
mesh_terms: D000818:Animals; D001483:Base Sequence; D002454:Cell Differentiation; D056970:Co-Repressor Proteins; D017931:DNA Primers / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D050416:Glucagon-Secreting Cells / Q000166:cytology* / Q000378:metabolism*; D000090322:Homeobox Protein Nkx-2.2; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D050417:Insulin-Secreting Cells / Q000166:cytology* / Q000378:metabolism*; D007515:Islets of Langerhans / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D008954:Models, Biological; D010641:Phenotype; D011401:Promoter Regions, Genetic; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D029961:Zebrafish Proteins
chemical_list: D056970:Co-Repressor Proteins; D017931:DNA Primers; D000090322:Homeobox Protein Nkx-2.2; D018398:Homeodomain Proteins; C000715627:Nkx2-2 protein, mouse; D011506:Proteins; D012097:Repressor Proteins; C104849:Tle3 protein, mouse; D015534:Trans-Activators; D014157:Transcription Factors; D029961:Zebrafish Proteins; C000715630:nkx2.2b protein, zebrafish; C084010:pancreatic and duodenal homeobox 1 protein