Pax6 Controls the Expression of Critical Genes Involved in Pancreatic α Cell Differentiation and Function*

Abstract

The paired box homeodomain Pax6 is crucial for endocrine cell development and function and plays an essential role in glucose homeostasis. Indeed, mutations of Pax6 are associated with diabetic phenotype. Importantly, homozygous mutant mice for Pax6 are characterized by markedly decreased ␤ and ␦ cells and absent ␣ cells. To better understand the critical role that Pax6 exerts in glucagon-producing cells, we developed a model of primary rat ␣ cells. To study the transcriptional network of Pax6 in adult and differentiated ␣ cells, we generated Pax6-deficient primary rat ␣ cells and glucagon-producing cells, using either specific siRNA or cells expressing constitutively a dominantnegative form of Pax6. In primary rat ␣ cells, we confirm that Pax6 controls the transcription of the Proglucagon and processing enzyme PC2 genes and identify three new target genes coding for MafB, cMaf, and NeuroD1/Beta2, which are all critical for Glucagon gene transcription and ␣ cell differentiation. Furthermore, we demonstrate that Pax6 directly binds and activates the promoter region of the three genes through specific binding sites and that constitutive expression of a dominant-negative form of Pax6 in glucagon-producing cells (InR1G9) inhibits the activities of the promoters. Finally our results suggest that the critical role of Pax6 action on ␣ cell differentiation is independent of those of Arx and Foxa2, two transcription factors that are necessary for ␣ cell development. We conclude that Pax6 is critical for ␣ cell function and differentiation through the transcriptional control of key genes involved in glucagon gene transcription, proglucagon processing, and ␣ cell differentiation.

Context-specific α-to-β-cell reprogramming by forced Pdx1 expression

“…4). Besides its endocrine progenitor function, Pax6 was implicated in the control of the transcription of several a-cell-associated genes, such as Gcg and MafB (Gosmain et al 2010). Interestingly, Pax4 could repress Pax6-mediated transactivation in vitro (Ritz-Laser et al 2002).…”

Deconstructing Pancreas Developmental Biology

“…4A) (Gosmain et al 2011). Pax6 mutants lack a cells, and have reduced glucagon expression and MafB expression, another regulator of glucagon expression that is selectively expressed in adult a cells in mice (Artner et al 2006;Nishimura et al 2006Nishimura et al , 2008Gosmain et al 2010). Regulation of glucagon processing may also be regulated by Foxa2.…”

Glucagon and α-cells as a novel therapeutic target in the management of diabetes mellitus

“…Отмечается, что Pax-6 необходим для дифференцировки Вопросы патогенеза L-клеток кишечника и экспрессии Gcg-гена в этих клет-ках. Предполагается, что продукция глюкагоноподобного пептида-1 (GLP-1) также может зависеть от Pax-6 [8].…”

“…Эксперименты на мышах, лишенных MafB, показали, что этот фактор регулирует основные этапы дифференцировки обоих типов клеток: и инсулин-, и глю-кагонпродуцирующих [8].…”