title: Characterization and regulation of the hb9/mnx1 beta-cell progenitor specific enhancer in zebrafish.
abstract: Differentiation of insulin producing beta-cells is a genetically well defined process that involves functions of various conserved transcription factors. Still, the transcriptional mechanisms underlying specification and determination of beta-cell fate are poorly defined. Here we provide the description of a beta-cell progenitor specific enhancer as a model to study initial steps of beta-cell differentiation. We show that evolutionary non-conserved upstream sequences of the zebrafish hb9 gene are required and sufficient for regulating expression in beta-cells prior to the onset of insulin expression. This enhancer contains binding sites for paired-box transcription factors and two E-boxes that in EMSA studies show interaction with Pax6b and NeuroD, respectively. We show that Pax6b is a potent activator of endodermal hb9 expression and that this activation depends on the beta-cell enhancer. Using genetic approaches we show that pax6b is crucial for maintenance but not induction of pancreatic hb9 transcription. As loss of Pax6b or Hb9 independently results in the loss of insulin expression, the data reveal a novel cross-talk between the two essential regulators of early beta-cell differentiation. While we find that the known pancreatic E-box binding proteins NeuroD and Ngn3 are not required for hb9 expression we also show that removal of both E-boxes selectively eliminates pancreatic specific reporter expression. The data provide evidence for an Ngn3 independent pathway of beta-cell specification that requires function of currently not specified E-box binding factors.
authors.affiliation: Institute for Molecular Biology/CMBI, Technikerstr. 25, University of Innsbruck, 6020 Innsbruck, Austria. A.Valeriya@gmx.de
authors.forename: Valeriya
authors.initials: V
authors.lastname: Arkhipova
authors.forename: Björn
authors.initials: B
authors.lastname: Wendik
authors.forename: Nathalie
authors.initials: N
authors.lastname: Devos
authors.forename: Olivier
authors.initials: O
authors.lastname: Ek
authors.forename: Bernard
authors.initials: B
authors.lastname: Peers
authors.forename: Dirk
authors.initials: D
authors.lastname: Meyer
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D051792:Basic Helix-Loop-Helix Proteins / Q000502:physiology; D002454:Cell Differentiation / Q000502:physiology; D019070:Cell Lineage / Q000502:physiology; D005136:Eye Proteins / Q000502:physiology*; D018398:Homeodomain Proteins / Q000502:physiology*; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000502:physiology; D007515:Islets of Langerhans / Q000166:cytology / Q000196:embryology; D009419:Nerve Tissue Proteins / Q000502:physiology; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors / Q000502:physiology*; D012097:Repressor Proteins / Q000502:physiology*; D015398:Signal Transduction; D013234:Stem Cells / Q000502:physiology; D014157:Transcription Factors / Q000502:physiology*; D015027:Zebrafish / Q000196:embryology*; D029961:Zebrafish Proteins / Q000502:physiology*
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D005136:Eye Proteins; D018398:Homeodomain Proteins; D009419:Nerve Tissue Proteins; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors; D012097:Repressor Proteins; D014157:Transcription Factors; D029961:Zebrafish Proteins; C531385:Mnx1 protein, zebrafish; C093564:Neurogenic differentiation factor 1