Gene knockout and transgenic technologies in risk assessment: The next generation

Abstract

Transgenic and knockout mice have been proposed as substitutes for one of the standard 2-yr rodent assays. The advantages of using genetically engineered mouse models is that fewer mice are needed, the time to develop disease is greatly reduced, and the mice are predisposed to developing cancer by virtue of gain or loss of functions. The models currently being used have yielded a large amount of data and have proved to be informative for risk assessment; however, they are still far from ideal. In fact, they inherently do not reflect the complexity of mutation and carcinogenesis in humans. Recent advances in technology and the creation of new knockout mice may produce more useful and more sensitive models. This review covers two recent advances in technology--inducible and regulatable gene expression and targeted genetic modifications in the genome--that will allow us to make better models. I also discuss new gene deletion and transgenic mouse models and their potential impact on risk-assessment assays. These models are presented in the context of four basic components or events that occur in the multistep process leading to cancer: maintenance of gene expression patterns, genome stability and DNA repair, cell-cell communication and signaling, and cell-cycle regulation. Finally, surrogate markers and utility in risk assessment are also discussed. This review is meant to stimulate further discussion in the field and to generate excitement about working toward the next generation of risk-assessment models.

The use of genetically modified mice in cancer risk assessment: Challenges and limitations

“…Significant progress has been made in recent years using these technologies (for reviews, see French et al, 2010; Gollapudi et al, 1998; Lynch et al, 2007; Macleod & Jacks, 1999; Pritchard et al, 2003; Rosenberg, 1997; Wells & Williams, 2009). GM animals are being actively used to investigate the role of specific xenobiotic metabolizing enzymes, DNA repair processes, cell-to-cell signaling, transcription factors, and gene expression, as well as cell cycle regulatory genes in tumor development (Boverhof et al, 2011; Gonzalez, 2001; Rosenberg, 1997). In most cases, the GM models which target specific genes and pathways differ substantially from the GM models described in this review which are primarily used to test or screen chemicals for carcinogenic effects.…”

Probing Human Cardiovascular Congenital Disease Using Transgenic Mouse Models

“…One encodes a tet-repressor herpes virus Vp16 termed rTA which is expressed either from a generic promoter that is nontissue-specific or from a developmentally regulated tissue-specific promoter. 85 The second construct (tetO) consists of a minimum promoter with no basal activity linked to the gene of interest. 85 The tet-V16 protein has a very high binding coefficient for the tetO.…”

“…85 The second construct (tetO) consists of a minimum promoter with no basal activity linked to the gene of interest. 85 The tet-V16 protein has a very high binding coefficient for the tetO. 85,86 There are two varieties of tet-regulatory sequences, one in which a gene is repressed by tet binding (rTA or “Tet-Off”) and the other where the gene is activated by tet binding (rtTA or “Tet-On”).…”

“…85 The tet-V16 protein has a very high binding coefficient for the tetO. 85,86 There are two varieties of tet-regulatory sequences, one in which a gene is repressed by tet binding (rTA or “Tet-Off”) and the other where the gene is activated by tet binding (rtTA or “Tet-On”). Repression of a gene with this system occurs because in the presence of tet or its analog, tet binds rTA and the confirmation changes so that it can no longer bind to the tetO sequence leading to downregulation of expression.…”

A Preliminary Operational Classification System for Nonmutagenic Modes of Action for Carcinogenesis

“…• As indicated earlier, observations that specific inhibition of the process signaled by the "biomarker" leads to a reduction in tumors or tumor-related DNA changes compatible with the dose response relationship described in the previous bullet. Such a specific inhibition may be produced, for example, by a chemical agent with a well-characterized specific action in the dosage used or an engineered genetic difference in a strain of experimental animals that knocks out the function of a particular gene (Rosenberg, 1997).…”