Chapter 062. Principles of Human Genetics (Part 10)

Transgenic Mice as Models of Genetic DiseaseSeveral organisms have been studied extensively as genetic models, including Mus musculus (mouse), Drosophila melanogaster (fruit fly), Caenorhabditis elegans (nematode), Saccharomyces cerevisiae (bakers yeast), and Escherichia coli (colonic bacterium). The ability to use these evolutionarily distant organisms as genetic models that are relevant to human physiology reflects a surprising conservation of genetic pathways and gene function. Transgenic mouse models have been particularly valuable, because many human and mouse genes exhibit similar structure and function, and because manipulation of the mouse genome is relatively straightforward compared to those of other mammalian species. ...
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Chapter 062. Principles of Human Genetics (Part 10) Chapter 062. Principles of Human Genetics (Part 10) Transgenic Mice as Models of Genetic Disease Several organisms have been studied extensively as genetic models,including Mus musculus (mouse), Drosophila melanogaster (fruit fly),Caenorhabditis elegans (nematode), Saccharomyces cerevisiae (bakers yeast),and Escherichia coli (colonic bacterium). The ability to use these evolutionarilydistant organisms as genetic models that are relevant to human physiology reflectsa surprising conservation of genetic pathways and gene function. Transgenicmouse models have been particularly valuable, because many human and mousegenes exhibit similar structure and function, and because manipulation of themouse genome is relatively straightforward compared to those of othermammalian species. Transgenic strategies in mice can be divided into two main approaches: (1)expression of a gene by random insertion into the genome, and (2) deletion ortargeted mutagenesis of a gene by homologous recombination with the nativeendogenous gene (knock-out, knock-in) (Fig. 62-6; Table 62-3). Transgenic miceare generated by pronuclear injection of foreign DNA into fertilized mouseoocytes and subsequent transfer into the oviduct of pseudopregnant foster mothers. Figure 62-6 Transgenic mouse models. Left. Transgenic mice are generated bypronuclear injection of foreign DNA into fertilized mouse oocytes and subsequenttransfer into the oviduct of pseudopregnant foster mothers. Right. For targetedmutagenesis (gene knock-out/knock-in), embryonic stem (ES) cells are transfectedwith the targeted (mutagenized) transgene. The transgene undergoes homologousrecombination with the wild-type gene. After selection, positive ES cells areintroduced into blastocysts and implanted into foster mothers. Chimeric mice canbe identified based on the mixed coat color of the offspring. Heterozygous miceare bred to obtain mice homozygous for the mutant allele. Table 62-3 Genetically Modified Animals Commonly Technical RemarksUsed Description Principle Transgenic Pronuclear Commonly used injection of transgene Genomic DNA or cDNA constructs Random integration of transgene Variable copy numbers of transgene Variable expression in each individual founder Gain-of-function models due to overexpression using tissue- specific promoters Loss-of-function models using anti-sense and dominant negative transgenes Inducible expression possible (Tetracycline, ecdysone) Applicable to several species (Targeted) Substitution of Predominantly used in miceKnock-out functional gene with inactive gene by Tissue-specific knock-out homologous possible (Cre/lox) recombination in Absence of phenotype embryonic stem cells possible due to redundancy (Targeted) Introduction of Predominantly used in miceKnock-in subtle mutation(s) into gene by substitution of Can accurately model human endogenous gene with disease gene carrying a specific mutation. Homologous recombination in embryonic stem cells Forward Mutations created Selection of phenotypegenetics randomly by ENU (N- followed by genetic characterization ...