The translation of novel discoveries from basic research to clinical application is a long, often inefficient, and thus costly process. Accordingly, the process of drug development requires optimization both for economic and for ethical reasons, in order to provide patients with appropriate treatments in a reasonable time frame. Consequently, "Translational Medicine" became a top priority in national and international roadmaps of human health research. Appropriate animal models for the evaluation of efficacy and safety of new drugs or therapeutic concepts are critical for the success of translational research. In this context rodent models are most widely used. At present, transgenic pigs are increasingly being established as large animal models for selected human diseases. The first pig whole genome sequence and many other genomic resources will be available in the near future. Importantly, efficient and precise techniques for the genetic modification of pigs have been established, facilitating the generation of tailored disease models. This article provides an overview of the current techniques for genetic modification of pigs and the transgenic pig models established for neurodegenerative diseases, cardiovascular diseases, cystic fibrosis, and diabetes mellitus.

The novel diabetic mouse model Munich Ins2C95S was discovered within the Munich N-ethyl-N-nitrosourea mouse mutagenesis screen. These mice exhibit a T3 A transversion in the insulin 2 (Ins2) gene at nucleotide position 1903 in exon 3, which leads to the amino acid exchange C95S and loss of the A6-A11 intrachain disulfide bond. From 1 month of age onwards, blood glucose levels of heterozygous Munich Ins2 C95S mutant mice were significantly increased compared with controls. The fasted and postprandial serum insulin levels of the heterozygous mutants were indistinguishable from those of wild-type littermates. However, serum insulin levels after glucose challenge, pancreatic insulin content, and homeostasis model assessment (HOMA) ␤-cell indices of heterozygous mutants were significantly lower than those of wild-type littermates. The initial blood glucose decrease during an insulin tolerance test was lower and HOMA insulin resistance indices were significantly higher in mutant mice, indicating the development of insulin resistance in mutant mice. The total islet volume, the volume density of ␤-cells in the islets, and the total ␤-cell volume of heterozygous male mutants was significantly reduced compared with wild-type mice. Electron microscopy of the ␤-cells of male mutants showed virtually no secretory insulin granules, the endoplasmic reticulum was severely enlarged, and mitochondria appeared swollen. Thus, Munich Ins2 C95S mutant mice are considered a valuable model to study the mechanisms of ␤-cell dysfunction and death during the development of diabetes.

BackgroundCurrently, genome-wide evaluation of cattle populations is based on SNP-genotyping using ~ 54 000 SNP. Increasing the number of markers might improve genomic predictions and power of genome-wide association studies. Imputation of genotypes makes it possible to extrapolate genotypes from lower to higher density arrays based on a representative reference sample for which genotypes are obtained at higher density.MethodsGenotypes using 639 214 SNP were available for 797 bulls of the Fleckvieh cattle breed. The data set was divided into a reference and a validation population. Genotypes for all SNP except those included in the BovineSNP50 Bead chip were masked and subsequently imputed for animals of the validation population. Imputation of genotypes was performed with Beagle, findhap.f90, MaCH and Minimac. The accuracy of the imputed genotypes was assessed for four different scenarios including 50, 100, 200 and 400 animals as reference population. The reference animals were selected to account for 78.03%, 89.21%, 97.47% and > 99% of the gene pool of the genotyped population, respectively.ResultsImputation accuracy increased as the number of animals and relatives in the reference population increased. Population-based algorithms provided highly reliable imputation of genotypes, even for scenarios with 50 and 100 reference animals only. Using MaCH and Minimac, the correlation between true and imputed genotypes was > 0.975 with 100 reference animals only. Pre-phasing the genotypes of both the reference and validation populations not only provided highly accurate imputed genotypes but was also computationally efficient. Genome-wide analysis of imputation accuracy led to the identification of many misplaced SNP.ConclusionsGenotyping key animals at high density and subsequent population-based genotype imputation yield high imputation accuracy. Pre-phasing the genotypes of the reference and validation populations is computationally efficient and results in high imputation accuracy, even when the reference population is small.

Model organisms like the mouse are important tools to learn more about gene function in man. Within the last 20 years many mutant mouse lines have been generated by different methods such as ENU mutagenesis, constitutive and conditional knock-out approaches, knock-down, introduction of human genes, and knock-in techniques, thus creating models which mimic human conditions. Due to pleiotropic effects, one gene may have different functions in different organ systems or time points during development. Therefore mutant mouse lines have to be phenotyped comprehensively in a highly standardized manner to enable the detection of phenotypes which might otherwise remain hidden. The German Mouse Clinic (GMC) has been established at the Helmholtz Zentrum München as a phenotyping platform with open access to the scientific community (www.mousclinic.de; [1]). The GMC is a member of the EUMODIC consortium which created the European standard workflow EMPReSSslim for the systemic phenotyping of mouse models (http://www.eumodic.org/[2]).

Transgenic pigs are promising donor organisms for xenotransplantation as they share many anatomical and physiological characteristics with humans. The most profound barrier to pig‐to‐primate xenotransplantation is the rejection of the grafted organ by a cascade of immune mechanisms commonly referred to as hyperacute rejection (HAR), acute humoral xenograft rejection (AHXR), immune cell‐mediated rejection, and chronic rejection. Various strategies for the genetic modification of pigs facilitate tailoring them to be donors for organ transplantation. Genetically modified pigs lacking alpha‐1,3‐Gal epitopes, the major xenoantigens triggering HAR of pig‐to‐primate xenografts, are considered to be the basis for further genetic modifications that can address other rejection mechanisms and incompatibilities between the porcine and primate blood coagulation systems. These modifications include expression of human complement regulatory proteins, CD39, endothelial protein C receptor, heme oxygenase 1, thrombomodulin, tissue factor pathway inhibitor as well as modulators of the cellular immune system such as human TNF alpha‐related apoptosis inducing ligand, HLA‐E/beta‐2‐microglobulin, and CTLA‐4Ig. In addition, transgenic strategies have been developed to reduce the potential risk of infections by endogenous porcine retroviruses. The protective efficacy of all these strategies is strictly dependent on a sufficiently high expression level of the respective factors with the required spatial distribution. This review provides an overview of the transgenic approaches that have been used to generate donor pigs for xenotransplantation, as well as their biological effects in in vitro tests and in preclinical transplantation studies. A future challenge will be to combine the most important and efficient genetic modifications in multi‐transgenic pigs for clinical xenotransplantation. Mol. Reprod. Dev. 77: 209–221, 2010. © 2009 Wiley‐Liss, Inc.