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Brown J, Su TT. E2F1, DIAP1, and the presence of a homologous chromosome promote while JNK inhibits radiation-induced loss of heterozygosity in Drosophila melanogaster. Genetics 2024; 226:iyad192. [PMID: 37874851 PMCID: PMC10763536 DOI: 10.1093/genetics/iyad192] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2023] [Revised: 08/25/2023] [Accepted: 10/04/2023] [Indexed: 10/26/2023] Open
Abstract
Loss of heterozygosity (LOH) can occur when a heterozygous mutant cell loses the remaining wild-type allele to become a homozygous mutant. LOH can have physiological consequences if, for example, the affected gene encodes a tumor suppressor. We used fluorescent reporters to study the mechanisms of LOH induction by X-rays, a type of ionizing radiation (IR), in Drosophila melanogaster larval wing discs. IR is used to treat more than half of patients with cancer, so understanding its effects is of biomedical relevance. Quantitative analysis of IR-induced LOH at different positions between the telomere and the centromere on the X chromosome showed a strong sex dependence and the need for a recombination-proficient homologous chromosome, whereas, paradoxically, position along the chromosome made little difference in LOH incidence. We propose that published data documenting high recombination frequency within centromeric heterochromatin on the X chromosome can explain these data. Using a focused screen, we identified E2F1 as a key promotor of LOH and further testing suggests a mechanism involving its role in cell-cycle regulation. We leveraged the loss of a transcriptional repressor through LOH to express transgenes specifically in cells that have already acquired LOH. This approach identified JNK signaling and apoptosis as key determinants of LOH maintenance. These studies reveal previously unknown mechanisms for the generation and elimination of cells with chromosome aberrations after exposure to IR.
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Affiliation(s)
- Jeremy Brown
- Department of Molecular, Cellular and Developmental Biology, 347 UCB, University of Colorado, Boulder, CO 80309-0347, USA
- Department of Cell and Developmental Biology, University of Colorado, Anschutz Medical Campus, 13001 E. 17th Pl., Aurora, CO 80045, USA
| | - Tin Tin Su
- Department of Molecular, Cellular and Developmental Biology, 347 UCB, University of Colorado, Boulder, CO 80309-0347, USA
- University of Colorado Cancer Center, Anschutz Medical Campus, 13001 E. 17th Pl., Aurora, CO 80045, USA
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Brown J, Su TT. E2F1 promotes, JNK and DIAP1 inhibit, and chromosomal position has little effect on radiation-induced Loss of Heterozygosity in Drosophila. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.05.09.540084. [PMID: 37214983 PMCID: PMC10197609 DOI: 10.1101/2023.05.09.540084] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Loss of Heterozygosity (LOH) can occur when a heterozygous mutant cell loses the remaining wild type allele to become a homozygous mutant. LOH can have physiological consequences if, for example, the affected gene encodes a tumor suppressor. We used two fluorescent reporters to study mechanisms of LOH induction by X-rays, a type of ionizing radiation (IR), in Drosophila larval wing discs. IR is used to treat more than half of cancer patients, so understanding its effects is of biomedical relevance. We report that IR-induced LOH does not correlate with the chromosomal position of the LOH locus, unlike previously shown for spontaneously occurring LOH. Like spontaneous LOH, however, IR-induced LOH of X-linked loci shows a sex-dependence, occurring predominately in females. A focused genetic screen identified E2F1 as a key promotor of LOH and further testing suggests a mechanism involving its role in cell cycle regulation rather than apoptosis. We combined the QF/QS LOH reporter with QUAS-transgenes to manipulate gene function after LOH induction. This approach identified JNK signaling and apoptosis as key determinants of LOH maintenance. These studies reveal previously unknown mechanisms for generation and maintenance of cells with chromosome aberrations after exposure to IR.
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Chick WS, Ludwig M, Zhao X, Kitzenberg D, Williams K, Johnson TE. Screening for stress-resistance mutations in the mouse. Front Genet 2014; 5:310. [PMID: 25250048 PMCID: PMC4157564 DOI: 10.3389/fgene.2014.00310] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2014] [Accepted: 08/19/2014] [Indexed: 11/13/2022] Open
Abstract
Longevity is correlated with stress resistance in many animal models. However, previous efforts through the boosting of the antioxidant defense system did not extend life span, suggesting that longevity related stress resistance is mediated by other uncharacterized pathways. We have developed a high-throughput platform for screening and rapid identification of novel genetic mutants in the mouse that are stress resistant. Selection for resistance to stressors occurs in mutagenized mouse embryonic stem (ES) cells, which are carefully treated so as to maintain pluripotency for mouse production. Initial characterization of these mutant ES cells revealed mutations in Pigl, Tiam1, and Rffl, among others. These genes are implicated in glycosylphosphatidylinositol biosynthesis, NADPH oxidase function, and inflammation. These mutants: (1) are resistant to two different oxidative stressors, paraquat and the omission of 2-mercaptoethanol, (2) have reduced levels of endogenous reactive oxygen species (ROS), (3) are capable of generating live mice, and (4) transmit the stress resistance phenotype to the mice. This strategy offers an efficient way to select for new mutants expressing a stress resistance phenotype, to rapidly identify the causative genes, and to develop mice for in vivo studies.
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Affiliation(s)
- Wallace S Chick
- Department of Cell and Developmental Biology, University of Colorado Denver Aurora, CO, USA ; Charles C. Gates Regenerative Medicine and Stem Cell Biology Program, University of Colorado Denver Aurora, CO, USA
| | - Michael Ludwig
- Department of Cell and Developmental Biology, University of Colorado Denver Aurora, CO, USA
| | - Xiaoyun Zhao
- Department of Cell and Developmental Biology, University of Colorado Denver Aurora, CO, USA
| | - David Kitzenberg
- Department of Cell and Developmental Biology, University of Colorado Denver Aurora, CO, USA
| | - Kristina Williams
- Department of Pediatrics, University of Colorado Denver Aurora, CO, USA
| | - Thomas E Johnson
- Department of Integrative Physiology, University of Colorado Boulder Boulder, CO, USA ; Institute for Behavioral Genetics, University of Colorado Boulder Boulder, CO, USA ; Biofrontiers Institute, University of Colorado Boulder Boulder, CO, USA
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Abstract
One of the most straightforward approaches to making novel biological discoveries is the forward genetic screen. The time is ripe for forward genetic screens in the mouse since the mouse genome is sequenced, but the function of many of the genes remains unknown. Today, with careful planning, such screens are within the reach of even small individual labs. In this chapter we first discuss the types of screens in existence, as well as how to design a screen to recover mutations that are relevant to the interests of a lab. We then describe how to create mutations using the chemical N-ethyl-N-nitrosourea (ENU), including a detailed injection protocol. Next, we outline breeding schemes to establish mutant lines for each type of screen. Finally, we explain how to map mutations using recombination and how to ensure that a particular mutation causes a phenotype. Our goal is to make forward genetics in the mouse accessible to any lab with the desire to do it.
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Affiliation(s)
- Vanessa L Horner
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA, USA.
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Hegg CC, Jia C, Chick WS, Restrepo D, Hansen A. Microvillous cells expressing IP3 receptor type 3 in the olfactory epithelium of mice. Eur J Neurosci 2010; 32:1632-45. [PMID: 20958798 DOI: 10.1111/j.1460-9568.2010.07449.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Microvillous cells of the main olfactory epithelium have been described variously as primary olfactory neurons, secondary chemosensory cells or non-sensory cells. Here we generated an IP3R3(tm1(tauGFP)) mouse in which the coding region for a fusion protein of tau and green fluorescent protein replaces the first exon of the Itpr3 gene. We provide immunohistochemical and functional characterization of the cells expressing IP3 receptor type 3 in the olfactory epithelium. These cells bear microvilli at their apex, and we therefore termed them IP3R3 MV cells. The cell body of these IP3R3 MV cells lies in the upper third of the main olfactory epithelium; a long thick basal process projects towards the base of the epithelium without penetrating the basal lamina. Retrograde labeling and unilateral bulbectomy corroborated that these IP3R3 MV cells do not extend axons to the olfactory bulb and therefore are not olfactory sensory neurons. The immunohistochemical features of IP3R3 MV cells varied, suggesting either developmental stages or the existence of subsets of these cells. Thus, for example, subsets of the IP3R3 MV cells make contact with substance P fibers or express the purinergic receptor P2X3. In addition, in recordings of intracellular calcium, these cells respond to ATP and substance P as well as to a variety of odors. The characterization of IP3R3 MV cells as non-neuronal chemoresponsive cells helps to explain the differing descriptions of microvillous cells in the literature.
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Affiliation(s)
- Colleen C Hegg
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI, USA
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Chick WS, Drechsel DA, Hammond W, Patel M, Johnson TE. Transmission of mutant phenotypes from ES cells to adult mice. Mamm Genome 2009; 20:734-40. [PMID: 19795169 DOI: 10.1007/s00335-009-9228-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2009] [Accepted: 09/04/2009] [Indexed: 10/20/2022]
Abstract
Genetic manipulation of embryonic stem (ES) cells has been used to produce genetically engineered mice modeling human disorders. Here we describe a novel, additional application: selection for a phenotype of interest and subsequent transmission of that phenotype to a living mouse. We show, for the first time, that a cellular phenotype induced by ENU mutagenesis in ES cells can be transmitted and recapitulated in adult mice derived from these cells. We selected for paraquat-resistant (PQ(R)) ES clones. Subsequent injection of these cells into blastocysts resulted in the production of germline chimeras, from which tail skin fibroblasts exhibited enhanced PQ(R). This trait was also recovered in progeny of the chimera. We avoided PQ toxicity, which blocks the ability to involve the germline, by developing a sib-selection method, one that could be widely applied wherever the selection itself might diminish the pluripotency of the ES cells. Thus, phenotype-driven screens in ES cells are both feasible and efficient in producing intact mouse models for in vivo studies.
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Affiliation(s)
- Wallace S Chick
- Department of Cell and Developmental Biology, University of Colorado Denver, Anschutz Medical Campus, Aurora, CO 80045, USA.
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Abstract
Chromosomal rearrangements, such as deletions, duplications, inversions and translocations, occur frequently in humans and can be disease-associated or phenotypically neutral. To understand the genetic consequences of such genomic changes, these mutations need to be modelled in experimentally tractable systems. The mouse is an excellent organism for this analysis because of its biological and genetic similarity to humans, the ease with which its genome can be manipulated and the similarity of observed affects. Through chromosome engineering, defined rearrangements can be introduced into the mouse genome. The resulting mouse models are leading to a better understanding of the molecular and cellular basis of dosage alterations in human disease phenotypes, in turn opening new diagnostic and therapeutic opportunities.
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Affiliation(s)
- Louise van der Weyden
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridgeshire, UK
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Xu M, You Y, Hunsicker P, Hori T, Small C, Griswold MD, Hecht NB. Mice deficient for a small cluster of Piwi-interacting RNAs implicate Piwi-interacting RNAs in transposon control. Biol Reprod 2008; 79:51-7. [PMID: 18401007 DOI: 10.1095/biolreprod.108.068072] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
The mammalian testis expresses a class of small noncoding RNAs that interact with mammalian PIWI proteins. In mice, the PIWI-interacting RNAs (piRNAs) partner with mammalian PIWI proteins, PIWIL1 and PIWIL2, also known as MIWI and MILI, to maintain transposon silencing in the germline genome. Here, we demonstrate that inactivation of Nct1/2, two noncoding RNAs encoding piRNAs, leads to derepression of LINE-1 (L1) but does not affect mouse viability, spermatogenesis, testicular gene expression, or fertility. These findings indicate that piRNAs from a cluster on chromosome 2 are necessary to maintain transposon silencing.
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Affiliation(s)
- Mingang Xu
- Center for Research on Reproduction and Women's Health, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6080, USA
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Ji S, You Y, Kerner J, Hoppel CL, Schoeb TR, Chick WS, Hamm DA, Sharer JD, Wood PA. Homozygous carnitine palmitoyltransferase 1b (muscle isoform) deficiency is lethal in the mouse. Mol Genet Metab 2008; 93:314-22. [PMID: 18023382 PMCID: PMC2270477 DOI: 10.1016/j.ymgme.2007.10.006] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/05/2007] [Accepted: 10/06/2007] [Indexed: 11/29/2022]
Abstract
Carnitine palmitoyltransferase-1 (CPT-1) catalyzes the rate-limiting step of mitochondrial beta-oxidation of long chain fatty acids (LCFA), the most abundant fatty acids in mammalian membranes and in energy metabolism. Human deficiency of the muscle isoform CPT-1b is poorly understood. In the current study, embryos with a homozygous knockout of Cpt-1b were lost before embryonic day 9.5-11.5. Also, while there were normal percentages of CPT-1b+/- pups born from both male and female CPT-1b+/- mice crossed with wild-type mates, the number of CPT-1b+/- pups from CPT-1b+/- breeding pairs was under-represented (63% of the expected number). Northern blot analysis demonstrated approximately 50% Cpt-1b mRNA expression in brown adipose tissue (BAT), heart and skeletal muscles in the CPT-1b+/- male mice. Consistent with tissue-specific expression of Cpt-1b mRNA in muscle but not liver, CPT-1+/- mice had approximately 60% CPT-1 activity in skeletal muscle and no change in total liver CPT-1 activity. CPT-1b+/- mice had normal fasting blood glucose concentration. Consistent with expression of CPT-1b in BAT and muscle, approximately 7% CPT-1b+/- mice (n=30) developed fatal hypothermia following a 3h cold challenge, while none of the CPT-1b+/+ mice (n=30) did. With a prolonged cold challenge (6h), significantly more CPT-1b+/- mice developed fatal hypothermia (52% CPT-1b+/- mice vs. 21% CPT-1b+/+ mice), with increased frequency in females of both genotypes (67% female vs. 38% male CPT-1b+/- mice, and 33% female vs. 8% male CPT-1b+/+ mice). Therefore, lethality of homozygous CPT-1b deficiency in the mice is consistent with paucity of human cases.
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Affiliation(s)
- Shaonin Ji
- Department of Genetics, University of Alabama at Birmingham, USA
| | - Yun You
- Mammalian Genetics & Genomics, Life Sciences Division, Oak Ridge National Laboratory, USA
| | - Janos Kerner
- Department of Nutrition, Case Western Reserve University, School of Medicine, Cleveland, OH, USA
| | - Charles L. Hoppel
- Department of Pharmacology, Case Western Reserve University, School of Medicine, Cleveland, OH, USA
- Department of Medicine, Case Western Reserve University, School of Medicine, Cleveland, OH, USA
| | | | - Wallace S.H. Chick
- Mammalian Genetics & Genomics, Life Sciences Division, Oak Ridge National Laboratory, USA
| | - Doug A. Hamm
- Department of Genetics, University of Alabama at Birmingham, USA
| | - J. Daniel Sharer
- Department of Genetics, University of Alabama at Birmingham, USA
| | - Philip A. Wood
- Department of Genetics, University of Alabama at Birmingham, USA
- Corresponding author. FAX: 205−975−4418 Telephone: 205−934−1303 e-mail: web: www.uab.edu/genetics
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