Brn-4 transcription factor expression targeted to the early developing mouse pancreas induces ectopic glucagon gene expression in insulin-producing beta cells

The endocrine pancreas is comprised of beta and alpha cells producing the glucostatic hormones insulin and glucagon, respectively, and arises during development by the differentiation of stem/progenitor cells in the foregut programmed by the beta cell lineage-specific homeodomain protein Idx-1. Brain-4 (Brn-4) is expressed in the pancreatic anlaga of the mouse foregut at e10 in the alpha cells and transactivates glucagon gene expression. We expressed Brn-4 in pancreatic precursors or beta cell lineage in transgenic mice by placing it under either Idx-1 or insulin promoter (rat insulin II promoter) control, respectively. Idx-1 expression occurs at developmental day e8.5, and insulin expression occurs at e9.5, respectively. Misexpression of Brn-4 by the Idx-1 promoter results in ectopic expression of the proglucagon gene in insulin-expressing pancreatic beta cells, whereas misexpression by rat insulin II promoter did not. The early developmental expression of Brn-4 appears to be a dominant regulator of the glucagon expressing alpha cell lineage, even in the context of the beta cell lineage.     

A complex array of positive and negative elements regulates the chicken alpha A-crystallin gene: involvement of Pax-6, USF, CREB and/or CREM, and AP-1 proteins.

The abundance of crystallins (> 80% of the soluble protein) in the ocular lens provides advantageous markers for selective gene expression during cellular differentiation. Here we show by functional and protein-DNA binding experiments that the chicken alpha A-crystallin gene is regulated by at least five control elements located at sites A (-148 to -139), B (-138 to -132), C (-128 to -101), D (-102 to -93), and E (-56 to -41). Factors interacting with these sites were characterized immunologically and by gel mobility shift experiments. The results are interpreted with the following model. Site A binds USF and is part of a composite element with site B. Site B binds CREB and/or CREM to enhance expression in the lens and binds an AP-1 complex including CREB, Fra2 and/or JunD which interacts with USF on site A to repress expression in fibroblasts. Sites C and E (which is conserved across species) bind Pax-6 in the lens to stimulate alpha A-crystallin promoter activity. These experiments provide the first direct data that Pax-6 contributes to the lens-specific expression of a crystallin gene. Site D (-104 to -93) binds USF and is a negative element. Thus, the data indicate that USF, CREB and/or CREM (or AP-1 factors), and Pax-6 bind a complex array of positive and negative cis-acting elements of the chicken alpha A-crystallin gene to control high expression in the lens and repression in fibroblasts.