Genetically-modified Mouse Strains Research Articles

Multiple and Consecutive Genome Editing Using i-GONAD and Breeding Enrichment Facilitates the Production of Genetically Modified Mice.

Genetically modified (GM) mice are essential tools in biomedical research. Traditional methods for generating GM mice are expensive and require specialized personnel and equipment. The use of clustered regularly interspaced short palindromic repeats (CRISPR) coupled with improved-Genome editing via Oviductal Nucleic Acids Delivery (i-GONAD) has highly increased the feasibility of producing GM mice in research laboratories. However, genetic modification in inbred mouse strains of interest such as C57BL/6 (B6) is still challenging because of their low fertility and embryo fragility. We have successfully generated multiple novel GM mouse strains in the B6 background while attempting to optimize i-GONAD. We found that i-GONAD reduced the litter size in superovulated pregnant females but did not impact pregnancy rates. Natural mating or low-hormone dose did not increase the low fertility rate observed in superovulated B6 females. However, diet enrichment had a positive effect on pregnancy success. We also optimized breeding conditions to increase the survival of small litters by co-housing i-GONAD-treated pregnant B6 females with synchronized pregnant FVB/NJ companion mothers. Thus, GM mice generation was increased by an enriched diet and shared pup rearing with highly fertile females such as FVB/NJ. In the present study, we generated 16 GM mice using a CRISPR/Cas system to target individual and multiple loci simultaneously or consecutively. We also compared homology-directed repair efficiency using different methods for LoxP insertion for conditional knockout mouse production. We found that a two-step serial LoxP insertion, in which each LoxP sequence was inserted individually in different i-GONAD procedures, was a low-risk high-efficiency method for generating floxed mice.

Mouse Lines with Cre-Mediated Recombination in Retinal Amacrine Cells

Amacrine cells (ACs) are the most diverse neuronal cell type in the vertebrate retina. Yet little is known about the contribution of ACs to visual processing and retinal disease. A major challenge in evaluating AC function is genetic accessibility. A classic tool of mouse genetics, Cre-mediated recombination, can provide such access. We have screened existing genetically-modified mouse strains and identified multiple candidates that express Cre-recombinase in subsets of retinal ACs. The Cre-expressing mice were crossed to fluorescent-reporter mice to assay Cre expression. In addition, a Cre-dependent fluorescent reporter plasmid was electroporated into the subretinal space of Cre strains. Herein, we report three mouse lines (Tac1::IRES-cre, Camk2a-cre, and Scx-cre) that express Cre recombinase in sub-populations of ACs. In two of these lines, recombination occurred in multiple AC types and a small number of other retinal cell types, while recombination in the Camk2a-cre line appears specific to a morphologically distinct AC. We anticipate that these characterized mouse lines will be valuable tools to the community of researchers who study retinal biology and disease.

The Aryl Hydrocarbon Receptor Attenuates Acute Cigarette Smoke-Induced Airway Neutrophilia Independent of the Dioxin Response Element.

Cigarette smoke is a prevalent respiratory toxicant that remains a leading cause of death worldwide. Cigarette smoke induces inflammation in the lungs and airways that contributes to the development of diseases such as lung cancer and chronic obstructive pulmonary disease (COPD). Due to the presence of aryl hydrocarbon receptor (AhR) ligands in cigarette smoke, activation of the AhR has been implicated in driving this inflammatory response. However, we have previously shown that the AhR suppresses cigarette smoke-induced pulmonary inflammation, but the mechanism by which the AhR achieves its anti-inflammatory function is unknown. In this study, we use the AhR antagonist CH-223191 to inhibit AhR activity in mice. After an acute (3-day) cigarette smoke exposure, AhR inhibition was associated with significantly enhanced neutrophilia in the airways in response to cigarette smoke, mimicking the phenotype of AhR-deficient mice. We then used genetically-modified mouse strains which express an AhR that can bind ligand but either cannot translocate to the nucleus or bind its cognate response element, to show that these features of the AhR pathway are not required for the AhR to suppress pulmonary neutrophilia. Finally, using the non-toxic endogenous AhR ligand FICZ, we provide proof-of-concept that activation of pulmonary AhR attenuates smoke-induced inflammation. Collectively, these results support the importance of AhR activity in mediating its anti-inflammatory function in response to cigarette smoke. Further investigation of the precise mechanisms by which the AhR exerts is protective functions may lead to the development of therapeutic agents to treat people with chronic lung diseases that have an inflammatory etiology, but for which few therapeutic options exist.

Mouse Models for Food Allergies: Where Do We Stand?

Food allergies are a steadily increasing health and economic problem. Immunologically, food allergic reactions are caused by pathological, allergen-specific Th2 responses resulting in IgE-mediated mast cell degranulation and associated inflammatory reactions. Clinically, food allergies are characterized by local inflammation of the mouth mucosa, the face, the throat, the gastrointestinal tract, are frequently paralleled by skin reactions, and can result in life-threatening anaphylactic reactions. To better understand food allergies and establish novel treatment options, mouse models are indispensable. This review discusses the available mouse food allergy models, dividing them into four categories: (1) adjuvant-free mouse models, (2) mouse models relying on adjuvants to establish allergen-specific Th2 responses, (3) mouse models using genetically-modified mouse strains to allow for easier sensitization, and (4) humanized mouse models in which different immunodeficient mouse strains are reconstituted with human immune or stem cells to investigate humanized immune responses. While most of the available mouse models can reproducibly portray the immunological parameters of food allergy (Th2 immune responses, IgE production and mast cell activation/expansion), so far, the recreation of the clinical parameters has proven more difficult. Therefore, up to now none of the available mouse models can reproduce the complete human pathology.

Assessing the tolerance to room temperature and viability of freeze-dried mice spermatozoa over long-term storage at room temperature under vacuum

Freeze-drying has been frequently used to preserve food and microorganisms at room temperature (RT) for extended periods of time; however, its application to mammalian species is difficult. Here, we developed a method to prolong the stability of freeze-dried (FD) mice spermatozoa at RT for more than one year without using any cryoprotectant agents. Our data showed that maintaining a vacuum in ampoules is critical to ensuring the viability of FD spermatozoa, as the stability of spermatozoa DNA increased when imperfectly vacuumed ampoules were detected using a non-destructive test and eliminated. Finally a large number of healthy offspring were obtained from mice oocytes fertilized with FD spermatozoa stored at RT for more than one year. Although the birth rate from three-month stored spermatozoa was lower than that from one-day stored spermatozoa, no further reduction was observed even in one-year stored spermatozoa. Therefore, FD spermatozoa preserved in this study were highly tolerant to warm temperatures. This method of storage shows a great potential for the preservation of genetic resources of mammalian species, such as genetically-modified mouse strains, without the use of electric power.

Role of the Immune System in Hypertension.

High blood pressure is present in more than one billion adults worldwide and is the most important modifiable risk factor of death resulting from cardiovascular disease. While many factors contribute to the pathogenesis of hypertension, a role of the immune system has been firmly established by a large number of investigations from many laboratories around the world. Immunosuppressive drugs and inhibition of individual cytokines prevent or ameliorate experimental hypertension, and studies in genetically-modified mouse strains have demonstrated that lymphocytes are necessary participants in the development of hypertension and in hypertensive organ injury. Furthermore, immune reactivity may be the driving force of hypertension in autoimmune diseases. Infiltration of immune cells, oxidative stress, and stimulation of the intrarenal angiotensin system are induced by activation of the innate and adaptive immunity. High blood pressure results from the combined effects of inflammation-induced impairment in the pressure natriuresis relationship, dysfunctional vascular relaxation, and overactivity of the sympathetic nervous system. Imbalances between proinflammatory effector responses and anti-inflammatory responses of regulatory T cells to a large extent determine the severity of inflammation. Experimental and human studies have uncovered autoantigens (isoketal-modified proteins and heat shock protein 70) of potential clinical relevance. Further investigations on the immune reactivity in hypertension may result in the identification of new strategies for the treatment of the disease.

Nucleotide-binding oligomerization domain-containing protein 2 (Nod2) modulates T1DM susceptibility by gut microbiota

Nucleotide-binding oligomerization domain-containing protein 2 (Nod2) is an innate immune receptor. To investigate the role of Nod2 in susceptibility to the autoimmune disease, type 1 diabetes mellitus (T1DM), we generated Nod2−/− non-obese diabetic (NOD) mice. The Nod2−/−NOD mice had different composition of the gut microbiota compared to Nod2+/+NOD mice and were significantly protected from diabetes, but only when housed separately from Nod2+/+NOD mice. This suggested that T1DM susceptibility in Nod2−/−NOD mice is dependent on the alteration of gut microbiota, which modulated the frequency and function of IgA-secreting B-cells and IL-10 promoting T-regulatory cells. Finally, colonizing germ-free NOD mice with Nod2−/−NOD gut microbiota significantly reduced pro-inflammatory cytokine-secreting immune cells but increased T-regulatory cells. Thus, gut microbiota modulate the immune system and T1D susceptibility. Importantly, our study raises a critical question about the housing mode in the interpretation of the disease phenotype of genetically-modified mouse strains in T1DM studies.

Revitalizing genetically-modified mouse strains using frozen-thawed sperm after up to 192 h of refrigerated epididymis transportation.

In the scientific interchange of genetically-modified mouse strains the transportation of refrigerated epididymis has several advantages over the transportation of live animals, especially with regard to the 3R (replacement, reduction and refinement) principles. The major limiting factor is the duration of the transportation. Previous reports have shown that sperm collected from transported epididymis maintained their fertility for around 72 h, but there are no published data with longer transportation times, and this window of time may be too short, especially for international shipments and where locations are not well connected. In this study live pups were born using frozen-thawed sperm after up to 192 h (8 days) of transportation, using a special invitro fertilization design which resulted in a fertilization rate of 10.5%.

Partial hepatectomy in mice.

The surgical procedure of two-thirds partial hepatectomy (PH) in rodents was first described more than 80 years ago by Higgins and Anderson. Nevertheless, this technique is still a state-of-the-art method for the community of liver researchers as it allows the in-depth analysis of signalling pathways involved in liver regeneration and hepatocarcinogenesis. The importance of PH as a key method in experimental hepatology has even increased in the last decade due to the increasing availability of genetically-modified mouse strains. Here, we propose a standard operating procedure (SOP) for the implementation of PH in mice, which is based on our experience of more than 10 years. In particular, the SOP offers all relevant background information on the PH model and provides comprehensive guidelines for planning and performing PH experiments. We provide established recommendations regarding optimal age and gender of animals, use of appropriate anaesthesia and biometric calculation of the experiments. We finally present an easy-to-follow step-by-step description of the complete surgical procedure including required materials, critical steps and postoperative management. This SOP especially takes into account the latest changes in animal welfare rules in the European Union but is still in agreement with current international regulations. In summary, this article provides comprehensive information for the legal application, design and implementation of PH experiments.

Abstract IA04: Targeting K-Ras signaling in lung and pancreatic adenocarcinomas

Abstract K-Ras oncogenes have been implicated in about one fifth of all human cancers including those with the worse prognosis including non-small cell lung carcinoma (NSCLC) and pancreatic ductal adenocarcinoma (PDAC). We have used genetic engineering strategies to develop genetically modified mouse (GEM) models that closely recapitulate the natural history of these human neoplasias. We have used these strains to validate targets of potential therapeutic value with the ultimate goal to translate these findings to the clinic. Briefly, we have crossed these GEM strains with mice that carried conditional knock out mutations in loci encoding potential therapeutic targets. These targets were ablated by genetic means (using inducible recombinases) either at the time of tumor initiation or, whenever possible, once the tumor has been generated. Then, we follow the fate of the tumor in the absence of the target that we wish to validate. This genetic-based strategy has significant advantages over classical pharmacological studies since it does not rely on the quality of the drug/inhibitor. For instance, the observed effects are always mechanism-based and not off-target effects. Moreover, if the target is eliminated systemically, our studies offer relevant information regarding potential toxic effects that may occur when the target would be pharmacologically inhibited in normal tissues. More recently, we are replacing the conditional knock strains by conditional knocked in mice so we will expressing kinase dead isoforms in tumor tissue instead of eliminating the target. We hope that this experimental approach will mimic more accurately those pharmacological responses that will be observed in the clinic. Using these experimental approaches, we have validated each of the K-Ras downstream kinases including those of the Raf/Mek/Erk pathway as well as the cell cycle Cdks. Our results have revealed some unexpected results which may have important implications for the development of future targeted therapies. For instance. whereas c-Raf is essential for the development of lung adenocarcinomas and pancreatic ductal adenocarcinomas, the closely related B-Raf and A-Raf kinases are completely dispensable. Thus demonstrating that K-Ras signaling does not proceed equally through the Raf kinases as previously thought. Likewise, lung adenocarciomas do not progress in the absence of Cdk4. However, ablation of the highly related cell cycle kinases Cdk2 and Cdk6 have no significant effect on tumor development. These observations underscore the need to carry out target validation studies using mouse models of cancer in order to design selective therapies that will have a greater chance of success in the clinic. Finally, we have also validated some upstream signaling effectors, mainly the EGFR for which there are already selective inhibitors in the clinic. Unexpectedly, whereas the EGFR has no therapeutic value in K-Ras driven lung adenocarcinomas as well intestinal tumors (as previously observed in the clinic), it is essential for the initiation of pancreatic tumors. These findings indicate that K-Ras oncogenic signaling may proceed through different effector pathways in a tissue specific manner, a finding that should also help to design more selective therapies. Citation Format: Mariano Barbacid. Targeting K-Ras signaling in lung and pancreatic adenocarcinomas. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr IA04. doi: 10.1158/1557-3125.RASONC14-IA04

Cochlear implantation in the mouse via the round window: Effects of array insertion

Animal models are the only means of assessing the effects of cochlear implantation (CI) at a cellular and molecular level. The range of naturally occurring and genetically-modified mouse strains which mimic human deafness provide excellent opportunities for auditory research. To date, there are very few studies of CI in mice. The main aims of this study were to develop a reproducible and viable technique to enable long term CI in the mouse and to assess the response of the mouse cochlea to implantation as a means of evaluating the success of the procedure. Electrode array implantation via the round window was performed in C57Bl/6 mice aged 3 and 6 months. The contralateral cochlea acted as a control. Auditory brainstem responses (ABR) were recorded prior to and following CI. Analysis showed greater threshold shifts in the implanted ear compared to the control ear post-implantation, but substantial preservation of hearing. There were no cases in which implantation caused a profound hearing loss across all frequencies. Cone beam computerised tomography and light microscopy confirmed correct placement of the electrode array within the scala tympani. Cochleae were prepared for histological examination. Initial analysis revealed encapsulation of the implant in tissue with morphological characteristics suggestive of fibrosis. Our results show that mouse CI via the round window offers a model for exploring tissue responses to implantation.

Simultaneous Detection of Multiple Transgenes for Genetically-Modified Mouse Strains

Recent advances in the genetic manipulation of mice have enabled us to generate transgenic and knockout mice. However, it is not easy to maintain these genetically-modified mice with the high-quality necessary to meet both scientific and legal requirements. RIKEN BRC has collected various transgenic, knockout, and conditional knockout mice. To examine the genetic modifications in these strains quickly and thoroughly, we established a simultaneous PCR test to detect multiple transgenes. We have called this, the "KO-survey". The PCR condition was optimized to detect neo, puro, pgk-neo, lacZ, and HSVtk-neo in set I, and hyg, IRES, cre, flp, and Gfp in set II. This "KO-survey" is useful for providing users with mouse strains of the highest genetic quality and accurate information on their genetic modifications.

Roles and regulation of the cardiac sodium channel Nav1.5: Recent insights from experimental studies

During the past decade, Na(v)1.5, the main voltage-gated Na(+) channel in the heart, has been shown to be involved in many cardiac diseases. Genetic variants in the gene SCN5A, encoding Na(v)1.5, have been linked to various cardiac phenotypes, such as the congenital and acquired long QT syndromes, Brugada syndrome, conduction slowing, sick sinus syndrome, atrial fibrillation, and even cases of dilated cardiomyopathy. This unexpected phenotypic diversity may reflect that Na(v)1.5 is not only restricted to the initiation of the action potential and rapid cardiac conduction, but may also be involved in other, not-yet elucidated, functions. Despite the fact that our understanding of the regulation of expression, localization, and function of Na(v)1.5 is deepening, we are still far from a comprehensive view. Much of our current knowledge has been obtained by carrying out experiments using "cellular expression systems", e.g. host cells expressing exogenous Na(v)1.5. Although very informative, these techniques are limited, in that Na(v)1.5 is not expressed in the physiological cellular environment of a cardiac cell. Recently, however, there have been several studies published which used approaches closer to "normal" or pathological physiology. In an attempt to summarize recently published data, this article will review the phenotypes of genetically-modified mouse strains where Na(v)1.5 expression and activity are directly or indirectly modified, as well as the regulation of Na(v)1.5 function using native cardiac myocytes. Despite obvious limitations, the reviewed studies provide an overview of the complex multi-factorial and multi-protein regulation of Na(v)1.5.

Of mice without pockets: mouse models to study the function of Rb family proteins

Three negative regulators of cell cycle, the related proteins, pRB, p107 and p130, constitute the family of pocket proteins. pRB is a tumor suppressor which has drawn a lot of attention on its family of proteins, with the ensuing intense study of their biology. As a result we have a wealth of information on their biochemistry and biology, ranging from their regulation to their biochemical activities, and the effects of their absence or overexpression on cells. Despite this, many questions remain unsolved. In recent years, analysis of genetically-modified mouse strains has provided interesting data regarding the physiological and pathophysiological roles of these three proteins. Specifically, germ-line and conditional knockout strains for one or more than one of the members of the family have revealed as powerful tools in this regard. Here we review the mouse models available for studying these cell cycle regulators and how data generated by these approaches have sometimes challenged previous thoughts about the pocket proteins biology.