Pancreatic ductal adenocarcinoma (PDA), one of the deadliest human cancers, often involves somatic activation of K-Ras oncogenes. We report that selective expression of an endogenous K-Ras(G12V) oncogene in embryonic cells of acinar/centroacinar lineage results in pancreatic intraepithelial neoplasias (PanINs) and invasive PDA, suggesting that PDA originates by differentiation of acinar/centroacinar cells or their precursors into ductal-like cells. Surprisingly, adult mice become refractory to K-Ras(G12V)-induced PanINs and PDA. However, if these mice are challenged with a mild form of chronic pancreatitis, they develop the full spectrum of PanINs and invasive PDA. These observations suggest that, during adulthood, PDA stems from a combination of genetic (e.g., somatic K-Ras mutations) and nongenetic (e.g., tissue damage) events.

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Adult liver has the unusual ability to fully regenerate after injury. Although regeneration is accomplished by the division of mature hepatocytes, the replicative potential of these cells is unknown. Here, the replicative capacity of adult liver cells and their medical usefulness as donor cells for transplantation were investigated by transfer of adult mouse liver cells into transgenic mice that display an endogenous defect in hepatic growth potential and function. The transplanted liver cell populations replaced up to 80 percent of the diseased recipient liver. These findings demonstrate the enormous growth potential of adult hepatocytes, indicating the feasibility of liver cell transplantation as a method to replace lost or diseased hepatic parenchyma.

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In a previous study we showed that genomic constructs were expressed more efficiently in transgenic mice than constructs that were identical except for the lack of introns. Using the mouse metallothionein promoter-rat growth hormone gene construct as a model, we show that the rrst intron ofthe rat growth hormone gene is essential for high-level expression, whereas the other three introns are less effective. Several heterologous introns placed 3' of the coding region of an intronless rat growth hormone gene are also ineffective. However, insertion of some heterologous introns between the metallothionein promoter and the growth hormone gene improves expression. To determine whether addition of heterologous introns would provide a general strategy for improving expression, we have tested them in conjunction with other intronless genes and with different promoters.In principle, it is possible to direct the expression of any gene to any specific cell type of an animal by using established transgenic methodology. This approach relies upon the fact that it is possible to combine the regulatory region(s) ofa gene that is expressed in a cell-specific manner with any mRNAencoding structural gene. The structural gene should then be transcribed according to the specificity dictated by the regulatory elements. This strategy has been used to explore a wide variety of fascinating developmental and physiological problems (see refs. 1-3 for reviews). However, not all gene constructs work well in transgenic mice. The two most common problems are inappropriate expression patterns and failure to achieve adequate expression levels.Inadequate expression is often associated with attempts to express cDNA constructs. The most baffling aspect of this phenomenon is that cDNA constructs that fail to work in transgenic mice are often expressed efficiently when transfected into tissue culture cells. These observations suggested that introns may be of special importance for achieving gene expression in transgenic mice. Because most of the early experiments that led to this suspicion were not well controlled, we set out to test it directly by comparing constructs that were identical except for the presence or absence of introns. With each of three test genes, mouse metallothionein I (mMT-I), mMT-rat growth hormone (rGH), and human ,3-globin (hf3G), we observed a striking improvement both in the number of transgenic mice that expressed the gene and in the average level of expression when the natural introns were included (4). Furthermore, nuclear run-on assays indicated that the introns had a major effect on transcription rather than mRNA processing or stability. Because the mMT and mMTrGH constructs showed no dependence on introns for expression after stable transfection into BHK (baby hamster kidney) cells, we postulated that introns may contain sequences that are recognized during embryogenesis.Introns could improve expression of transgenes by a number of different mechanisms. For example, some introns may contain enhancers or other ...

A general purpose algorithm for the solution of nonlinear mathematical programming problems containing integer, discrete, zero-one, and continuous design variables is described. The algorithm implements a branch and bound procedure in conjunction with either an exterior penalty function or a quadratic programming method. Variable bounds are handled independently from the design constraints which removes the necessity to reformulate the problem at each branching node. Examples are presented to demonstrate the utility of the algorithm for solving design problems.

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The ability to unambiguously mark a cell's genotype is essential for studies in which genetically distinct cell populations must be distinguished from one another in vivo. One approach to this challenge has been the creation of transgenic mice expressing a transgene marker that is easily detectable, with no background staining. Multiple transgenic mouse strains bearing constructs with different combinations of promoter elements and coding sequences have been described, each with its own advantages and limitations. In this report we describe the use of an 800-bp promoter fragment isolated from the beta(geo) integration site in ROSA26 mice to target expression of two marker genes. We demonstrate that the ROSA26 promoter directs ubiquitous expression of human placental alkaline phosphatase and enhanced green fluorescent protein during embryonic and postnatal development in mouse and rat. We further demonstrate the general utility of these transgenes for marking donor cells in transplantation studies.