MafA is a dedicated activator of the insulin gene in vivo.
As successful generation of insulin-producing cells could be used for diabetes treatment, a concerted effort is being made to understand the molecular programs underlying islet beta-cell formation and function. The closely related MafA and MafB transcription factors are both key mammalian beta-cell regulators. MafA and MafB are co-expressed in insulin+beta-cells during embryogenesis, while in the adult pancreas only MafA is produced in beta-cells and MafB in glucagon+alpha-cells. MafB-/- animals are also deficient in insulin+ and glucagon+ cell production during embryogenesis. However, only MafA over-expression selectively induced endogenous Insulin mRNA production in cell line-based assays, while MafB specifically promoted Glucagon expression. Here, we analyzed whether these factors were sufficient to induce insulin+ and/or glucagon+ cell formation within embryonic endoderm using the chick in ovo electroporation assay. Ectopic expression of MafA, but not MafB, promoted Insulin production; however, neither MafA nor MafB were capable of inducing Glucagon. Co-electroporation of MafA with the Ngn3 transcription factor resulted in the development of more organized cell clusters containing both insulin- and glucagon-producing cells. Analysis of chimeric proteins of MafA and MafB demonstrated that chick Insulin activation depended on sequences within the MafA C-terminal DNA-binding domain. MafA was also bound to Insulin and Glucagon transcriptional control sequences in mouse embryonic pancreas and beta-cell lines. Collectively, these results demonstrate a unique ability for MafA to independently activate Insulin transcription.
Artner
Isabella
I
Departments of, Molecular Physiology and Biophysics Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, Tennessee 37205, USA. isabella.artner@med.lu.se
Hang
Yan
Y
Guo
Min
M
Gu
Guoqiang
G
Stein
Roland
R
D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D002642:Chick Embryo; D004247:DNA / Q000378:metabolism; D018274:Electroporation; D004707:Endoderm / Q000378:metabolism; D005934:Glucagon / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007150:Immunohistochemistry; D007328:Insulin / Q000235:genetics* / Q000378:metabolism; D007515:Islets of Langerhans / Q000378:metabolism; D050977:Maf Transcription Factors / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D051258:MafB Transcription Factor / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D051379:Mice; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D055503:Protein Multimerization / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction
D051792:Basic Helix-Loop-Helix Proteins; D004247:DNA; D005934:Glucagon; D007328:Insulin; D050977:Maf Transcription Factors; D051258:MafB Transcription Factor; D009419:Nerve Tissue Proteins; C407737:Neurog3 protein, mouse