Islet β-Cell-Specific MafA Transcription Requires the 5′-Flanking Conserved Region 3 Control Domain

Abstract

MafA is a key transcriptional activator of islet ␤ cells, and its exclusive expression within ␤ cells of the developing and adult pancreas is distinct among pancreatic regulators. Region 3 (base pairs ؊8118 to ؊7750 relative to the transcription start site), one of six conserved 5 cis domains of the MafA promoter, is capable of directing ␤-cell-line-selective expression. Transgenic reporters of region 3 alone (R3), sequences spanning regions 1 to 6 (R1-6; base pairs ؊10428 to ؉230), and R1-6 lacking R3 (R1-6 ⌬R3 ) were generated. Only the R1-6 transgene was active in MafA ؉ insulin ؉ cells during development and in adult cells. R1-6 also mediated glucose-induced MafA expression. Conversely, pancreatic expression was not observed with the R3 or R1-6 ⌬R3 line, although much of the nonpancreatic expression pattern was shared between the R1-6 and R1-6 ⌬R3 lines. Further support for the importance of R3 was also shown, as the islet regulators Nkx6.1 and Pax6, but not NeuroD1, activated MafA in gel shift, chromatin immunoprecipitation (ChIP), and transfection assays and in vivo mouse knockout models. Lastly, ChIP demonstrated that Pax6 and Pdx-1 also bound to R1 and R6, potentially functioning in pancreatic and nonpancreatic expression. These data highlight the nature of the cisand trans-acting factors controlling the ␤-cell-specific expression of MafA.

Pax6 Is Crucial for β-Cell Function, Insulin Biosynthesis, and Glucose-Induced Insulin Secretion

“…6). Pax6 overexpression led to a significant activation of the insulin 1 gene promoter as previously described (4), as well as the Pdx1 and MafA gene promoters (data not shown) (7,8). We thus assessed the effect of Pax6 overexpression on the newly identified target gene promoters; each promoter was specifically activated from 2-to 3.5-fold, indicating that Pax6 transactivates these promoters (Fig.…”

“…Indeed, Pax6 has previously been reported to directly bind and activate Pdx1 and MafA gene promoters (7,8). There is actually a close interrelationship between these factors, because Pax6 controls Pdx1 and MafA, whereas MafA controls Pdx1 and vice versa (21).…”

PAX6 maintains β cell identity by repressing genes of alternative islet cell types

“…steady-state mRNA levels of the CreER and insulin mRNAs are likely the result of very different rates of mRNA degradation, as the insulin mRNA has a half-life in excess of 3 days in rodent β cells (58). We also examined the expression dynamics of Mafa, a direct activator of insulin transcription and a known target of PAX6 (59). The reduction in Mafa mRNA was rapid and occurred maximally already 1 week after tamoxifen administration, as with the kinetics of Pax6 loss.…”

Genomic Control Processes in Adult Body Part Formation

“…Sources: For references to linkages that had been established earlier, see caption to predecessor of this GRN (Davidson, 2006, p. 179). More recent sources of data supporting the linkages shown in this GRN model, both positive and negative, are as follows: PTF1 to ptf1a, PTF1 to exocrine genes, PTF1 to RBP-JL (Beres et al, 2006); (ptf1a, RBP-JL) to pdx1 (Miyatsuka et al, 2007;Wiebe et al, 2007); (mafa, mafb) to pdx1 (Vanhoose et al, 2008); (foxa1, foxa2) to pdx1 (Gao et al, 2008); (foxa, nkx2.2, pdx1) to mafa (Raum et al, 2006); glis3 to mafa, glis3 to insulin, glis3 to pdx1, glis3 to ngn3 (Fernandez-Zapico et al, 2009;Kang et al, 2009); (islet1, hnf4a) to insulin, (Eeckhoute et al, 2006;Zhang et al, 2009);(meis, pbx1, pbx2) to pax6 (Zhang et al, 2006;Delporte et al, 2008); nkx6.1 to hnf1α (Donelan et al, 2010); (nkx2.2, ngn3) to neuroD (Anderson et al, 2009); (pdx1, gata4) to gata4 (Rojas et al, 2009);(nkx6.1, pdx1, pax6) to mafa (Raum et al, 2010); foxa to gata4 (Rojas et al, 2010); pax6 to mafb, pax6 to c-maf, pax6 to neuroD1, and (mafb, neuroD1, foxa1, foxa2) to glucagon (Gosmain et al, 2010); islet1 to arx (Liu et al, 2011); dac to cyc21 (Kalousova et al, 2010); hnf1a to mafa ; pdx1 to pax6 (Delporte et al, 2008); ngn3 to ia1 (Mellitzer et al, 2006); hnf4a to hnf1α (Lu et al, 2008); pax6 to glucagon (Grapp et al, 2009); pbx1 to glucagon (Liu et al, 2006); (pax6, cmaf) to glucagon ; nk6.1 to glucagon (Gauthier et al, 2007); brn4 to glucagon, (pdx1, mafa, neuroD) to pander (Burkhardt et al, 2008); alx3 to insulin (Mirasierra and Vallejo, 2006;Mirasierra et al, ...…”