The PAX6 gene is activated by the basic helix–loop–helix transcription factor NeuroD/BETA2

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Abstract
PAX6 is a transcription factor that plays an important role during pancreatic morphogenesis. The aim of the present study is to identify the upstream activator(s) of the PAX6 gene possibly involved in the early stages of pancreatic differentiation. Recently, individual elements regulating PAX6 gene activity in the pancreas have been identified in a 1100 bp Spe/HincII fragment 4.6 kb upstream of exon 0. Preliminary sequence analysis of this region revealed some potential DNA-binding sites (E boxes) specific for the binding of basic helix–loop–helix transcription factors. By using electrophoretic mobility shift assays, we demonstrated that both nuclear protein extracts from insulin-secreting RINm5F cells and in vitro-translated NeuroD/BETA2 can bind specifically to these E boxes. Furthermore, by transient transfection experiments we demonstrated that the expression of basic helix–loop–helix transcription factor NeuroD/BETA2 can induce activation of the PAX6 promoter in the NIH-3T3 cell line. Thus we show that NeuroD/BETA2 is involved in the activation of the expression of PAX6 through E boxes in the PAX6 promoter localized in a 1.1 kb sequence within the 4.6 kb untranslated region upstream of exon 0.