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El-Saadi MW, Tian X, Grames M, Ren M, Keys K, Li H, Knott E, Yin H, Huang S, Lu XH. Tracing brain genotoxic stress in Parkinson's disease with a novel single-cell genetic sensor. SCIENCE ADVANCES 2022; 8:eabd1700. [PMID: 35427151 PMCID: PMC9012470 DOI: 10.1126/sciadv.abd1700] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2020] [Accepted: 03/01/2022] [Indexed: 05/06/2023]
Abstract
To develop an in vivo tool to probe brain genotoxic stress, we designed a viral proxy as a single-cell genetic sensor termed PRISM that harnesses the instability of recombinant adeno-associated virus genome processing and a hypermutable repeat sequence-dependent reporter. PRISM exploits the virus-host interaction to probe persistent neuronal DNA damage and overactive DNA damage response. A Parkinson's disease (PD)-associated environmental toxicant, paraquat (PQ), inflicted neuronal genotoxic stress sensitively detected by PRISM. The most affected cell type in PD, dopaminergic (DA) neurons in substantia nigra, was distinguished by a high level of genotoxic stress following PQ exposure. Human alpha-synuclein proteotoxicity and propagation also triggered genotoxic stress in nigral DA neurons in a transgenic mouse model. Genotoxic stress is a prominent feature in PD patient brains. Our results reveal that PD-associated etiological factors precipitated brain genotoxic stress and detail a useful tool for probing the pathogenic significance in aging and neurodegenerative disorders.
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Affiliation(s)
- Madison Wynne El-Saadi
- Department of Pharmacology, Toxicology and Neuroscience, Louisiana State University Health, Shreveport, Shreveport, LA 71103, USA
| | - Xinli Tian
- Department of Pharmacology, Toxicology and Neuroscience, Louisiana State University Health, Shreveport, Shreveport, LA 71103, USA
| | - Mychal Grames
- Department of Pharmacology, Toxicology and Neuroscience, Louisiana State University Health, Shreveport, Shreveport, LA 71103, USA
| | - Michael Ren
- Department of Pharmacology, Toxicology and Neuroscience, Louisiana State University Health, Shreveport, Shreveport, LA 71103, USA
| | - Kelsea Keys
- Department of Pharmacology, Toxicology and Neuroscience, Louisiana State University Health, Shreveport, Shreveport, LA 71103, USA
| | - Hanna Li
- Department of Pharmacology, Toxicology and Neuroscience, Louisiana State University Health, Shreveport, Shreveport, LA 71103, USA
| | - Erika Knott
- Department of Pharmacology, Toxicology and Neuroscience, Louisiana State University Health, Shreveport, Shreveport, LA 71103, USA
| | - Hong Yin
- Feist-Weiller Cancer Center and Department of Medicine, Louisiana State University Health, Shreveport, Shreveport, LA 71103, USA
| | - Shile Huang
- Department of Biochemistry and Molecular Biology, Louisiana State University Health, Shreveport, Shreveport, LA 71103, USA
| | - Xiao-Hong Lu
- Department of Pharmacology, Toxicology and Neuroscience, Louisiana State University Health, Shreveport, Shreveport, LA 71103, USA
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Genetically-directed Sparse Neuronal Labeling in BAC Transgenic Mice through Mononucleotide Repeat Frameshift. Sci Rep 2017; 7:43915. [PMID: 28272512 PMCID: PMC5341054 DOI: 10.1038/srep43915] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2016] [Accepted: 01/30/2017] [Indexed: 12/18/2022] Open
Abstract
Mosaicism with Repeat Frameshift (MORF) allows a single Bacterial Artificial Chromosome (BAC) transgene to direct sparse labeling of genetically-defined neuronal populations in mice. The BAC transgene drives cell-type-specific transcription of an out-of-frame mononucleotide repeat that is placed between a translational start codon and a membrane-bound fluorescent protein lacking its start codon. The stochastic frameshift of the unstable repeat DNA in a subset of BAC-expressing neurons results in the in-frame translation of the reporter protein hence the sparse neuronal labeling. As a proof-of-concept, we generated D1-dopamine receptor (D1) BAC MORF mice that label about 1% striatal D1-expressing medium spiny neurons and allow visualization of their dendrites. These mice enable the study of D1-MSN dendrite development in wildtype mice, and its degeneration in a mouse model of Huntington’s disease.
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Single cell lineage tracing reveals a role for TgfβR2 in intestinal stem cell dynamics and differentiation. Proc Natl Acad Sci U S A 2016; 113:12192-12197. [PMID: 27791005 DOI: 10.1073/pnas.1611980113] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Intestinal stem cells (ISCs) are maintained by a niche mechanism, in which multiple ISCs undergo differential fates where a single ISC clone ultimately occupies the niche. Importantly, mutations continually accumulate within ISCs creating a potential competitive niche environment. Here we use single cell lineage tracing following stochastic transforming growth factor β receptor 2 (TgfβR2) mutation to show cell autonomous effects of TgfβR2 loss on ISC clonal dynamics and differentiation. Specifically, TgfβR2 mutation in ISCs increased clone survival while lengthening times to monoclonality, suggesting that Tgfβ signaling controls both ISC clone extinction and expansion, independent of proliferation. In addition, TgfβR2 loss in vivo reduced crypt fission, irradiation-induced crypt regeneration, and differentiation toward Paneth cells. Finally, altered Tgfβ signaling in cultured mouse and human enteroids supports further the in vivo data and reveals a critical role for Tgfβ signaling in generating precursor secretory cells. Overall, our data reveal a key role for Tgfβ signaling in regulating ISCs clonal dynamics and differentiation, with implications for cancer, tissue regeneration, and inflammation.
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Mcilhatton MA, Boivin GP, Groden J. Manipulation of DNA Repair Proficiency in Mouse Models of Colorectal Cancer. BIOMED RESEARCH INTERNATIONAL 2016; 2016:1414383. [PMID: 27413734 PMCID: PMC4931062 DOI: 10.1155/2016/1414383] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/18/2016] [Accepted: 05/09/2016] [Indexed: 12/20/2022]
Abstract
Technical and biological innovations have enabled the development of more sophisticated and focused murine models that increasingly recapitulate the complex pathologies of human diseases, in particular cancer. Mouse models provide excellent in vivo systems for deciphering the intricacies of cancer biology within the context of precise experimental settings. They present biologically relevant, adaptable platforms that are amenable to continual improvement and refinement. We discuss how recent advances in our understanding of tumorigenesis and the underlying deficiencies of DNA repair mechanisms that drive it have been informed by using genetically engineered mice to create defined, well-characterized models of human colorectal cancer. In particular, we focus on how mechanisms of DNA repair can be manipulated precisely to create in vivo models whereby the underlying processes of tumorigenesis are accelerated or attenuated, dependent on the composite alleles carried by the mouse model. Such models have evolved to the stage where they now reflect the initiation and progression of sporadic cancers. The review is focused on mouse models of colorectal cancer and how insights from these models have been instrumental in shaping our understanding of the processes and potential therapies for this disease.
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Affiliation(s)
- Michael A. Mcilhatton
- Department of Cancer Biology and Genetics, The Ohio State University, 460 West 12th Avenue, Columbus, OH 43210, USA
| | - Gregory P. Boivin
- Department of Pathology, Boonshoft School of Medicine, Wright State University, Health Sciences Building 053, 3640 Colonel Glenn Highway, Dayton, OH 45435, USA
| | - Joanna Groden
- Department of Cancer Biology and Genetics, The Ohio State University, 460 West 12th Avenue, Columbus, OH 43210, USA
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An intact Pms2 ATPase domain is not essential for male fertility. DNA Repair (Amst) 2015; 39:46-51. [PMID: 26753533 DOI: 10.1016/j.dnarep.2015.12.011] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2015] [Revised: 12/23/2015] [Accepted: 12/23/2015] [Indexed: 01/08/2023]
Abstract
The DNA mismatch repair (MMR) machinery in mammals plays critical roles in both mutation avoidance and spermatogenesis. Meiotic analysis of knockout mice of two different MMR genes, Mlh1 and Mlh3, revealed both male and female infertility associated with a defect in meiotic crossing over. In contrast, another MMR gene knockout, Pms2 (Pms2(ko/ko)), which contained a deletion of a portion of the ATPase domain, produced animals that were male sterile but female fertile. However, the meiotic phenotype of Pms2(ko/ko) males was less clear-cut than for Mlh1- or Mlh3-deficient meiosis. More recently, we generated a different Pms2 mutant allele (Pms2(cre)), which results in deletion of the same portion of the ATPase domain. Surprisingly, Pms2(cre/cre) male mice were completely fertile, suggesting that the ATPase domain of Pms2 is not required for male fertility. To explore the difference in male fertility, we examined the Pms2 RNA and found that alternative splicing of the Pms2(cre) allele results in a predicted Pms2 containing the C-terminus, which contains the Mlh1-interaction domain, a possible candidate for stabilizing Mlh1 levels. To study further the basis of male fertility, we examined Mlh1 levels in testes and found that whereas Pms2 loss in Pms2(ko/ko) mice results in severely reduced levels of Mlh1 expression in the testes, Mlh1 levels in Pms2(cre/cre) testes were reduced to a lesser extent. Thus, we propose that a primary function of Pms2 during spermatogenesis is to stabilize Mlh1 levels prior to its critical crossing over function with Mlh3.
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Stiedl P, Grabner B, Zboray K, Bogner E, Casanova E. Modeling cancer using genetically engineered mice. Methods Mol Biol 2015; 1267:3-18. [PMID: 25636462 DOI: 10.1007/978-1-4939-2297-0_1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Genetically engineered mouse (GEM) models have proven to be a powerful tool to study tumorigenesis. The mouse is the preferred complex organism used in cancer studies due to the high number and versatility of genetic tools available for this species. GEM models can mimic point mutations, gene amplifications, short and large deletions, translocations, etc.; thus, most of the genetic aberrations found in human tumors can be modeled in GEM, making GEM models a very attractive system. Furthermore, recent developments in mouse genetics may facilitate the generation of GEM models with increased mutational complexity, therefore resembling human tumors better. Within this review, we will discuss the different possibilities of modeling tumorigenesis using GEM and the future developments within the field.
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Affiliation(s)
- Patricia Stiedl
- Ludwig Boltzmann Institute for Cancer Research (LBI-CR), Währinger Str. 13a, Vienna, 1090, Austria
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Wen M, Gao Y, Wang L, Ran L, Li J, Luo K. Split-Cre complementation restores combination activity on transgene excision in hair roots of transgenic tobacco. PLoS One 2014; 9:e110290. [PMID: 25329460 PMCID: PMC4201524 DOI: 10.1371/journal.pone.0110290] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2014] [Accepted: 09/10/2014] [Indexed: 12/03/2022] Open
Abstract
The Cre/loxP system is increasingly exploited for genetic manipulation of DNA in vitro and in vivo. It was previously reported that inactive ''split-Cre'' fragments could restore Cre activity in transgenic mice when overlapping co-expression was controlled by two different promoters. In this study, we analyzed recombination activities of split-Cre proteins, and found that no recombinase activity was detected in the in vitro recombination reaction in which only the N-terminal domain (NCre) of split-Cre protein was expressed, whereas recombination activity was obtained when the C-terminal (CCre) or both NCre and CCre fragments were supplied. We have also determined the recombination efficiency of split-Cre proteins which were co-expressed in hair roots of transgenic tobacco. No Cre recombination event was observed in hair roots of transgenic tobacco when the NCre or CCre genes were expressed alone. In contrast, an efficient recombination event was found in transgenic hairy roots co-expressing both inactive split-Cre genes. Moreover, the restored recombination efficiency of split-Cre proteins fused with the nuclear localization sequence (NLS) was higher than that of intact Cre in transgenic lines. Thus, DNA recombination mediated by split-Cre proteins provides an alternative method for spatial and temporal regulation of gene expression in transgenic plants.
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Affiliation(s)
- Mengling Wen
- Key Laboratory of Eco-environments of Three Gorges Reservoir Region, Ministry of Education, Institute of Resources Botany, School of Life Sciences, Southwest University, Chongqing, China
- Chongqing Key Laboratory of Transgenic Plant and Safety Control, Southwest University, Chongqing, China
| | - Yuan Gao
- Key Laboratory of Eco-environments of Three Gorges Reservoir Region, Ministry of Education, Institute of Resources Botany, School of Life Sciences, Southwest University, Chongqing, China
- Chongqing Key Laboratory of Transgenic Plant and Safety Control, Southwest University, Chongqing, China
| | - Lijun Wang
- Key Laboratory of Eco-environments of Three Gorges Reservoir Region, Ministry of Education, Institute of Resources Botany, School of Life Sciences, Southwest University, Chongqing, China
- Chongqing Key Laboratory of Transgenic Plant and Safety Control, Southwest University, Chongqing, China
| | - Lingyu Ran
- Key Laboratory of Eco-environments of Three Gorges Reservoir Region, Ministry of Education, Institute of Resources Botany, School of Life Sciences, Southwest University, Chongqing, China
- Chongqing Key Laboratory of Transgenic Plant and Safety Control, Southwest University, Chongqing, China
| | - Jiahui Li
- Key Laboratory of Eco-environments of Three Gorges Reservoir Region, Ministry of Education, Institute of Resources Botany, School of Life Sciences, Southwest University, Chongqing, China
- Chongqing Key Laboratory of Transgenic Plant and Safety Control, Southwest University, Chongqing, China
| | - Keming Luo
- Key Laboratory of Eco-environments of Three Gorges Reservoir Region, Ministry of Education, Institute of Resources Botany, School of Life Sciences, Southwest University, Chongqing, China
- Chongqing Key Laboratory of Transgenic Plant and Safety Control, Southwest University, Chongqing, China
- Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining, China
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Koole W, Tijsterman M. Mosaic analysis and tumor induction in zebrafish by microsatellite instability-mediated stochastic gene expression. Dis Model Mech 2014; 7:929-36. [PMID: 24487406 PMCID: PMC4073281 DOI: 10.1242/dmm.014365] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mosaic analysis, in which two or more populations of cells with differing genotypes are studied in a single animal, is a powerful approach to study developmental mechanisms and gene function in vivo. Over recent years, several genetic methods have been developed to achieve mosaicism in zebrafish, but despite their advances, limitations remain and different approaches and further refinements are warranted. Here, we describe an alternative approach for creating somatic mosaicism in zebrafish that relies on the instability of microsatellite sequences during replication. We placed the coding sequences of various marker proteins downstream of a microsatellite and out-of-frame; in vivo frameshifting into the proper reading frame results in expression of the protein in random individual cells that are surrounded by wild-type cells. We optimized this approach for the binary Gal4-UAS expression system by generating a driver line and effector lines that stochastically express Gal4-VP16 or UAS:H2A-EGFP and self-maintaining UAS:H2A-EGFP-Kaloop, respectively. To demonstrate the utility of this system, we stochastically expressed a constitutively active form of the human oncogene H-RAS and show the occurrence of hyperpigmentation and sporadic tumors within 5 days. Our data demonstrate that inducing somatic mosaicism through microsatellite instability can be a valuable approach for mosaic analysis and tumor induction in Danio rerio.
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Affiliation(s)
- Wouter Koole
- Department of Toxicogenetics, Leiden University Medical Center, Leiden, 2333 ZC, The Netherlands
| | - Marcel Tijsterman
- Department of Toxicogenetics, Leiden University Medical Center, Leiden, 2333 ZC, The Netherlands.
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Kang H, Shibata D. Direct measurements of human colon crypt stem cell niche genetic fidelity: the role of chance in non-darwinian mutation selection. Front Oncol 2013; 3:264. [PMID: 24133655 PMCID: PMC3796283 DOI: 10.3389/fonc.2013.00264] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2013] [Accepted: 09/25/2013] [Indexed: 01/06/2023] Open
Abstract
Perfect human stem cell genetic fidelity would prevent aging and cancer. However, perfection would be difficult to achieve, and aging is universal and cancers common. A hypothesis is that because mutations are inevitable over a human lifetime, downstream mechanisms have evolved to manage the deleterious effects of beneficial and lethal mutations. In the colon, a crypt stem cell architecture reduces the number of mitotic cells at risk for mutation accumulation, and multiple niche stem cells ensure that a lethal mutation within any single stem cell does not lead to crypt death. In addition, the architecture of the colon crypt stem cell niche may harness probability or chance to randomly discard many beneficial mutations that might lead to cancer. An analysis of somatic chromosome copy number alterations (CNAs) reveals a lack of perfect fidelity in individual normal human crypts, with age-related increases and higher frequencies in ulcerative colitis, a proliferative, inflammatory disease. The age-related increase in somatic CNAs appears consistent with relatively normal replication error and cell division rates. Surprisingly, and similar to point mutations in cancer genomes, the types of crypt mutations were more consistent with random fixation rather than selection. In theory, a simple “non-Darwinian” way to nullify selection is to reduce the size of the reproducing population. Fates are more determined by chance rather than selection in very small populations, and therefore selection may be minimized within small crypt niches. The desired effect is that many beneficial mutations that might lead to cancer are randomly lost by drift rather than fixed by selection. The subdivision of the colon into multiple very small stem cell niches may trade Darwinian evolution for non-Darwinian somatic cell evolution, capitulating to aging but reducing cancer risks.
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Affiliation(s)
- Haeyoun Kang
- Department of Pathology, CHA Bundang Medical Center, CHA University , Seongnam-si , South Korea
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Fischer JM, Schepers AG, Clevers H, Shibata D, Liskay RM. Occult progression by Apc-deficient intestinal crypts as a target for chemoprevention. Carcinogenesis 2013; 35:237-46. [PMID: 23996931 DOI: 10.1093/carcin/bgt296] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Although Apc mutation is widely considered an initiating event in colorectal cancer, little is known about the earliest stages of tumorigenesis following sporadic Apc loss. Therefore, we have utilized a novel mouse model that facilitates the sporadic inactivation of Apc via frameshift reversion of Cre in single, isolated cells and subsequently tracks the fates of Apc-deficient intestinal cells. Our results suggest that consistent with Apc being a 'gatekeeper', loss of Apc early in life during intestinal growth leads to adenomas or increased crypt fission, manifested by fields of mutant but otherwise normal-appearing crypts. In contrast, Apc loss occurring later in life has minimal consequences, with mutant crypts being less prone to either increased crypt fission or adenoma formation. Using the stem cell-specific Lgr5-CreER mouse, we generated different sized fields of Apc-deficient crypts via independent recombination events and found that field size correlates with progression to adenoma. To evaluate this early stage prior to adenoma formation as a therapeutic target, we examined the chemopreventive effects of sulindac on Apc-deficient occult crypt fission. We found that sulindac treatment started early in life inhibits the morphologically occult spread of Apc-deficient crypts and thus reduces adenoma numbers. Taken together these results suggest that: (i) earlier Apc loss promotes increased crypt fission, (ii) a field of Apc-deficient crypts, which can form via occult crypt fission or independent neighboring events, is an important intermediate between loss of Apc and adenoma formation and (iii) normal-appearing Apc-deficient crypts are potential unappreciated targets for cancer screening and chemoprevention.
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Affiliation(s)
- Jared M Fischer
- Department of Molecular and Medical Genetics, Oregon Health and Science University, Portland, OR 97239, USA
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Washington MK, Powell AE, Sullivan R, Sundberg J, Wright N, Coffey RJ, Dove WF. Pathology of rodent models of intestinal cancer: progress report and recommendations. Gastroenterology 2013; 144:705-17. [PMID: 23415801 PMCID: PMC3660997 DOI: 10.1053/j.gastro.2013.01.067] [Citation(s) in RCA: 83] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/17/2012] [Revised: 01/26/2013] [Accepted: 01/31/2013] [Indexed: 12/21/2022]
Abstract
In October 2010, a pathology review of rodent models of intestinal neoplasia was held at The Jackson Laboratory. This review complemented 2 other concurrent events: a workshop on methods of modeling colon cancer in rodents and a conference on current issues in murine and human colon cancer. We summarize the results of the pathology review and the committee's recommendations for tumor nomenclature. A virtual high-resolution image slide box of these models has been developed. This report discusses significant recent developments in rodent modeling of intestinal neoplasia, including the role of stem cells in cancer and the creation of models of metastatic intestinal cancer.
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Affiliation(s)
- Mary Kay Washington
- Department of Pathology, Vanderbilt University Medical Center, Nashville, TN
| | - Anne E. Powell
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN
| | - Ruth Sullivan
- University of Wisconsin Madison Carbone Cancer Center, Research Animal Resources Center, and Laboratory for Optical and Computational Instrumentation, Madison, WI
| | - John Sundberg
- The Jackson Laboratory, Bar Harbor, ME and Department of Medicine, Vanderbilt University Medical Center, Nashville, TN
| | - Nicholas Wright
- Barts Cancer Institute, Barts and the London School of Medicine, Queen Mary University of London
| | - Robert J. Coffey
- Departments of Medicine and Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN and Department of Veterans Affairs Medical Center, Nashville, TN
| | - William F. Dove
- McArdle Laboratory for Cancer Research, Department of Oncology, University of Wisconsin, Madison, WI
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Hair cell replacement in adult mouse utricles after targeted ablation of hair cells with diphtheria toxin. J Neurosci 2013; 32:15093-105. [PMID: 23100430 DOI: 10.1523/jneurosci.1709-12.2012] [Citation(s) in RCA: 134] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
We developed a transgenic mouse to permit conditional and selective ablation of hair cells in the adult mouse utricle by inserting the human diphtheria toxin receptor (DTR) gene into the Pou4f3 gene, which encodes a hair cell-specific transcription factor. In adult wild-type mice, administration of diphtheria toxin (DT) caused no significant hair cell loss. In adult Pou4f3(+/DTR) mice, DT treatment reduced hair cell numbers to 6% of normal by 14 days post-DT. Remaining hair cells were located primarily in the lateral extrastriola. Over time, hair cell numbers increased in these regions, reaching 17% of untreated Pou4f3(+/DTR) mice by 60 days post-DT. Replacement hair cells were morphologically distinct, with multiple cytoplasmic processes, and displayed evidence for active mechanotransduction channels and synapses characteristic of type II hair cells. Three lines of evidence suggest replacement hair cells were derived via direct (nonmitotic) transdifferentiation of supporting cells: new hair cells did not incorporate BrdU, supporting cells upregulated the pro-hair cell gene Atoh1, and supporting cell numbers decreased over time. This study introduces a new method for efficient conditional hair cell ablation in adult mouse utricles and demonstrates that hair cells are spontaneously regenerated in vivo in regions where there may be ongoing hair cell turnover.
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Abstract
APC is considered a gatekeeper for colorectal cancer (CRC). Cells with heterozygous APC mutations have altered expression profiles suggesting that the first APC hit may help set the stage for subsequent transformation. Therefore, we measured transformation efficiency following what we have designated as “simultaneous” versus “stepwise” Apc loss. We combined a conditional Apc allele (ApcCKO) with a Cre reporter gene and an out-of-frame Cre allele (Pms2cre) that stochastically becomes functional by a frameshift mutation in single cells. Loss of one Apc allele (ApcCKO/+) had little consequence, whereas simultaneous loss of both Apc alleles (ApcCKO/CKO) resulted in increased clonal expansion (crypt fission), consistent with the gatekeeper function of Apc. Interestingly, our analyses showed that most of the Apc-deficient crypts in ApcCKO/CKO mice appeared normal, with morphologic transformation, including β-catenin deregulation, occurring in only 17% of such crypts. To determine whether transformation efficiency was different following stepwise Apc loss, we combined ApcCKO with a germline mutant allele, either ApcMin or Apc1638N. Transformation efficiency following stepwise Apc loss (ApcMin/CKO or Apc1638N/CKO) was increased 5-fold and essentially all of the Apc-deficient cells were dysplastic. In summary, our data suggest that the gatekeeper function of Apc consists of two roles, clonal expansion and morphologic transformation, because simultaneous Apc loss frequently leads to occult clonal expansion without morphologic transformation, whereas stepwise Apc loss more often results in visible neoplasia. Finally, that Apc-deficient cells in certain scenarios can retain a normal phenotype is unexpected and may have clinical implications for surveillance strategies to prevent CRC.
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Abstract
Animal models of cancer have been instrumental in understanding the progression and therapy of hereditary cancer syndromes. The ability to alter the genome of an individual mouse cell in both constitutive and inducible approaches has led to many novel insights into their human counterparts. In this review, knockout mouse models of inherited human cancer syndromes are presented and insights from the study of these models are highlighted.
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Affiliation(s)
- Sohail Jahid
- Department of Biological Chemistry, University of California Irvine, Irvine, CA, USA
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Xue Y, Johnson R, Desmet M, Snyder PW, Fleet JC. Generation of a transgenic mouse for colorectal cancer research with intestinal cre expression limited to the large intestine. Mol Cancer Res 2010; 8:1095-104. [PMID: 20663863 DOI: 10.1158/1541-7786.mcr-10-0195] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Genetically modified mice have been used for colon cancer research, but findings from these models are confounded by expression of cancer in multiple organs. We sought to create a transgenic mouse with Cre recombinase (Cre) expression limited to the epithelial cells of the large intestine and used this model to study colon cancer driven by adenomatosis polyposis coli (APC) gene inactivation. A promoter/enhancer from the mouse carbonic anhydrase I gene was used to generate a Cre-expressing transgenic mouse (CAC). After characterizing transgene expression and distribution, CAC mice were crossed to APC(580S) mice to generate mice with APC inactivation at one (CAC;APC(580S/+)) or both alleles (CAC;APC(580S/580S)). Transgene expression was limited to the epithelial cells of the cecum and colon, extended from the crypt base to the luminal surface, and was expressed in approximately 15% of the crypts. No abnormal gross phenotype was seen in 3- or 6-week-old CAC;APC(580S/+) mice, but CAC;APC(580S/580S) mice had significant mucosal hyperplasia in the colon at 3 weeks, which developed into tumors by 6 weeks. By 10 weeks, 20% of CAC;APC(580S/+) mice developed adenomatous lesions in the distal colon (3.0 +/- 0.4 mm; 1.1 per mouse). Dextran sulfate sodium treatment increased the incidence and number of tumors, and this occurred predominantly in distal colon. Our new model has improved features for colon cancer research, that is, transgene expression is limited to the epithelium of the large bowel with normal cells found next to genetically modified cells.
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Affiliation(s)
- Yingben Xue
- Purdue University, West Lafayette, IN 47906-2059, USA
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Abstract
Genetically engineered mice are essential tools in both mechanistic studies and drug development in colon cancer research. Mice with mutations in the Apc gene, as well as in genes that modify or interact with Apc, are important models of familial adenomatous polyposis. Mice with mutations in the beta-catenin signaling pathway have also revealed important information about colon cancer pathogenesis, along with models for hereditary nonpolyposis colon cancer and inflammatory bowel diseases associated with colon cancer. Finally, transplantation models (xenografts)have been useful in the study of metastasis and for testing potential therapeutics. This review discusses what models have been developed most recently and what they have taught us about colon cancer formation, progression, and possible treatment strategies.
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Affiliation(s)
- Makoto Mark Taketo
- Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York, USA
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Fischer JM, Stringer JR. Mutation in aging mice occurs in diverse cell types that proliferate postmutation. Aging Cell 2008; 7:667-80. [PMID: 18652575 DOI: 10.1111/j.1474-9726.2008.00416.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
To determine the relationship between aging, cell proliferation and mutation in different cell types, hearts, brains and kidneys from G11 PLAP mice between 1 week and 24 months of age were examined. Mutant cells were detected in tissue sections by staining for Placental Alkaline Phosphatase (PLAP) activity, an activity that marks cells that have sustained a frameshift mutation in a mononucleotide tract inserted into the coding region of the human gene encoding PLAP. The number of PLAP(+) cells increased with age in all three tissues. The types of cells exhibiting a mutant phenotype included cells that are proliferative, such as kidney epithelial cells, and cells that do not frequently replicate, such as cardiac muscle cells and neurons. In the brain, PLAP(+) cells appeared in various locations and occurred at similar frequencies in different regions. Within the cerebellum, PLAP(+) Purkinje cell neurons appeared at a rate similar to that seen in the brain as a whole. PLAP(+) cells were observed in kidney-specific cell types such as those in glomeruli and collecting tubules, as well as in connective tissue and blood vessels. In the heart, PLAP(+) cells appeared to be cardiac muscle cells. Regardless of tissue and cell type, PLAP(+) cells occurred as singletons and in clusters, both of which increased in frequency with age. These data show that age-associated accumulation of mutant cells occurs in diverse cell types and is due to both new mutation and proliferation of mutant cells, even in cell types that tend to not proliferate.
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Affiliation(s)
- Richard Fishel
- Department of Molecular Virology, Immunology and Medical Genetics, Ohio State University Medical Center, Columbus, Ohio 43210, USA.
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