Ulf Ahlgren

Current techniques for three-dimensional (3D) optical microscopy (deconvolution, confocal microscopy, and optical coherence tomography) generate 3D data by "optically sectioning" the specimen. This places severe constraints on the maximum thickness of a specimen that can be imaged. We have developed a microscopy technique that uses optical projection tomography (OPT) to produce high-resolution 3D images of both fluorescent and nonfluorescent biological specimens with a thickness of up to 15 millimeters. OPT microscopy allows the rapid mapping of the tissue distribution of RNA and protein expression in intact embryos or organ systems and can therefore be instrumental in studies of developmental biology or gene function.

To study the late beta-cell-specific function of the homeodomain protein IPF1/PDX1 we have generated mice in which the Ipf1/Pdx1 gene has been disrupted specifically in beta cells. These mice develop diabetes with age, and we show that IPF1/PDX1 is required for maintaining the beta cell identity by positively regulating insulin and islet amyloid polypeptide expression and by repressing glucagon expression. We also provide evidence that IPF1/PDX1 regulates the expression of Glut2 in a dosage-dependent manner suggesting that lowered IPF1/PDX1 activity may contribute to the development of type II diabetes by causing impaired expression of both Glut2 and insulin.

We have previously shown that mice carrying a null mutation in the homeobox gene ipf1, now renamed to pdx1, selectively lack a pancreas. To elucidate the level at which PDX1 is required during the development of the pancreas, we have in this study analyzed the early stages of pancreas ontogeny in PDX-/- mice. These analyses have revealed that the early inductive events leading to the formation of the pancreatic buds and the appearance of the early insulin and glucagon cells occur in the PDX1-deficient embryos. However, the subsequent morphogenesis of the pancreatic epithelium and the progression of differentiation of the endocrine cells are arrested in the pdx1-/- embryos. In contrast, the pancreatic mesenchyme grows and develops, both morphologically and functionally, independently of the epithelium. We also show that the pancreatic epithelium in the pdx1 mutants is unable to respond to the mesenchymal-derived signal(s) which normally promote pancreatic morphogenesis. Together these data provide evidence that PDX-1 acts cell autonomously and that the lack of a pancreas in the pdx1-/- mice is due to a defect in the pancreatic epithelium.