Pax6 controls the expression of critical genes involved in pancreatic {alpha} cell differentiation and function.
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 β and δ cells and absent α cells. To better understand the critical role that Pax6 exerts in glucagon-producing cells, we developed a model of primary rat α cells. To study the transcriptional network of Pax6 in adult and differentiated α cells, we generated Pax6-deficient primary rat α cells and glucagon-producing cells, using either specific siRNA or cells expressing constitutively a dominant-negative form of Pax6. In primary rat α 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 α 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 α cell differentiation is independent of those of Arx and Foxa2, two transcription factors that are necessary for α cell development. We conclude that Pax6 is critical for α cell function and differentiation through the transcriptional control of key genes involved in glucagon gene transcription, proglucagon processing, and α cell differentiation.
Gosmain
Yvan
Y
From the Diabetes Unit, Division of Endocrinology, Diabetes and Nutrition, University Hospital, 1211 Geneva 4, Switzerland. Electronic address: Yvan.Gosmain@hcuge.ch.
Marthinet
Eric
E
From the Diabetes Unit, Division of Endocrinology, Diabetes and Nutrition, University Hospital, 1211 Geneva 4, Switzerland.
Cheyssac
Claire
C
From the Diabetes Unit, Division of Endocrinology, Diabetes and Nutrition, University Hospital, 1211 Geneva 4, Switzerland.
Guérardel
Audrey
A
From the Diabetes Unit, Division of Endocrinology, Diabetes and Nutrition, University Hospital, 1211 Geneva 4, Switzerland.
Mamin
Aline
A
From the Diabetes Unit, Division of Endocrinology, Diabetes and Nutrition, University Hospital, 1211 Geneva 4, Switzerland.
Katz
Liora S
LS
From the Diabetes Unit, Division of Endocrinology, Diabetes and Nutrition, University Hospital, 1211 Geneva 4, Switzerland.
Bouzakri
Karim
K
Department of Genetic Medicine and Development, University Medical Center, University of Geneva, 1211 Geneva 4, Switzerland.
Philippe
Jacques
J
From the Diabetes Unit, Division of Endocrinology, Diabetes and Nutrition, University Hospital, 1211 Geneva 4, Switzerland.
D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D002460:Cell Line; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology*; D050416:Glucagon-Secreting Cells / Q000166:cytology / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008954:Models, Biological; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors / Q000235:genetics / Q000378:metabolism*; D052336:Proglucagon / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D020218:Response Elements / Q000502:physiology*
D005136:Eye Proteins; D018398:Homeodomain Proteins; D000071841:PAX6 Transcription Factor; C000605730:PAX6 protein, human; D051761:Paired Box Transcription Factors; C000605732:Pax6 protein, mouse; C000605733:Pax6 protein, rat; D012097:Repressor Proteins; D052336:Proglucagon