Regulation of c-maf gene expression by Pax6 in cultured cells

c-Maf is a bZip transcription factor expressed in developmental and cellular differentiation processes, Recently, a c-maf knockout mouse model, showing abnormal lens development, has been reported, In order to study the regulation mechanisms of c-maf gene expression during the differentiation process we have Cloned and functionally characterized the rat c-maf (maf-2) gene. The rat c-maf gene is an intronless gene, covering a length of 3.5 kb. Transient transfection analysis of the 5'-flanking region of the c-maf gene using luciferase as the reporter gene shows that Pax6. a master transcription factor for lens development, strongly activates the c-maf promoter construct, Endogenous c-maf is also activated by the Pax6 expression-vector. Electrophoresis mobility shift assay and DNase 1 footprinting analysis show that at least three Pax6-binding sites are located in the 5'-flanking and 5'-non-coding regions of the rat c-maf gene, The c-maf gene was also markedly activated by its own product, c-Maf, through the MARE (Maf recognition element), suggesting that a positive autoregulatory mechanism controls this gene, In situ hybridization histochemical detection of Pax6 and c-Maf in the E14 lens showed that both mRNAs are expressed in the lens equator where lens epithelial cells are differentiating to lens fiber cells. These results suggest that a Pax6/c-Maf transcription factor cascade is working in lens development.