New routes for transgenesis of the mouse

Investigation of the molecular biology underlying the pronounced high gene targeting frequency at the Myh9 gene locus in mouse embryonic stem cells

The generation of genetically modified mouse models derived from gene targeting (GT) in mouse embryonic stem (ES) cells (mESCs) has greatly advanced both basic and clinical research. Our previous finding that gene targeting at the Myh9 exon2 site in mESCs has a pronounced high homologous recombination (HR) efficiency (>90%) has facilitated the generation of a series of nonmuscle myosin II (NM II) related mouse models. Furthermore, the Myh9 gene locus has been well demonstrated to be a new safe harbor for site-specific insertion of other exogenous genes. In the current study, we intend to investigate the molecular biology underlying for this high HR efficiency from other aspects. Our results confirmed some previously characterized properties and revealed some unreported observations: 1) The comparison and analysis of the targeting events occurring at the Myh9 and several widely used loci for targeting transgenesis, including ColA1, HPRT, ROSA26, and the sequences utilized for generating these targeting constructs, indicated that a total length about 6 kb with approximate 50% GC-content of the 5’ and 3’ homologous arms, may facilitate a better performance in terms of GT efficiency. 2) Despite increasing the length of the homologous arms, shifting the targeting site from the Myh9 exon2, to intron2, or exon3 led to a gradually reduced GT frequency (91.7, 71.8 and 50.0%, respectively). This finding provides the first evidence that the HR frequency may also be associated with the targeting site even in the same locus. Meanwhile, the decreased trend of the GT efficiency at these targeting sites was consistent with the reduced percentage of simple sequence repeat (SSR) and short interspersed nuclear elements (SINEs) in the sequences for generating the targeting constructs, suggesting the potential effects of these DNA elements on GT efficiency; 3) Our series of targeting experiments and analyses with truncated 5’ and 3’ arms at the Myh9 exon2 site demonstrated that GT efficiency positively correlates with the total length of the homologous arms (R = 0.7256, p<0.01), confirmed that a 2:1 ratio of the length, a 50% GC-content and the higher amount of SINEs for the 5’ and 3’ arms may benefit for appreciable GT frequency. Though more investigations are required, the Myh9 gene locus appears to be an ideal location for identifying HR-related cis and trans factors, which in turn provide mechanistic insights and also facilitate the practical application of gene editing.

Identification and characterization of MYH9 locus for high efficient gene knock-in and stable expression in mouse embryonic stem cells

Targeted integration of exogenous genes into so-called safe harbors/friend sites, offers the advantages of expressing normal levels of target genes and preventing potentially adverse effects on endogenous genes. However, the ideal genomic loci for this purpose remain limited. Additionally, due to the inherent and unresolved issues with the current genome editing tools, traditional embryonic stem (ES) cell-based targeted transgenesis technology is still preferred in practical applications. Here, we report that a high and repeatable homologous recombination (HR) frequency (>95%) is achieved when an approximate 6kb DNA sequence flanking the MYH9 gene exon 2 site is used to create the homology arms for the knockout/knock-in of diverse nonmuscle myosin II (NM II) isoforms in mouse ES cells. The easily obtained ES clones greatly facilitated the generation of multiple NM II genetic replacement mouse models, as characterized previously. Further investigation demonstrated that though the targeted integration site for exogenous genes is shifted to MYH9 intron 2 (about 500bp downstream exon 2), the high HR efficiency and the endogenous MYH9 gene integrity are not only preserved, but the expected expression of the inserted gene(s) is observed in a pre-designed set of experiments conducted in mouse ES cells. Importantly, we confirmed that the expression and normal function of the endogenous MYH9 gene is not affected by the insertion of the exogenous gene in these cases. Therefore, these findings suggest that like the commonly used ROSA26 site, the MYH9 gene locus may be considered a new safe harbor for high-efficiency targeted transgenesis and for biomedical applications.

Development and identification of Set transgenic mice

As a multifunctional protein involved in numerous biological processes, Set is expressed in several embryonic and adult organs. Furthermore, Set is overexpressed in numerous types of human cancers, including acute myeloid leukemia, breast cancer and pancreatic cancer. The expression of Set in germ cells is involved in gonad development, and the overexpression of Set has been observed in polycystic ovaries. In order to elucidate the physiological and pathological roles of Set, a Set transgenic mouse model was developed, in which the global overexpression of Set in adult tissues could be induced via the Cre/loxP system with the precise deletion of the Stop fragment in double-transgenic hybrids. This result was then confirmed by genotypical and protein analysis using polymerase chain reaction and bioluminescence imaging. In conclusion, the conditional Set transgenic mice carrying a reporter system were successfully generated. The transgenic mice open a new window for the further investigation of the function of Set using tissue-specific Cre mice and inducible Cre systems.

Mouse Models for the Study of Synthesis, Secretion, and Action of Pituitary Gonadotropins

Gonadotropins play fundamental roles in reproduction. More than 30years ago, Cga transgenic mice were generated, and more than 20years ago, the phenotypes of Cga null mice were reported. Since then, numerous mouse strains have been generated and characterized to address several questions in reproductive biology involving gonadotropin synthesis, secretion, and action. More recently, extragonadal expression, and in some cases, functions of gonadotropins in nongonadal tissues have been identified. Several genomic and proteomic approaches including novel mouse genome editing tools are available now. It is anticipated that these and other emerging technologies will be useful to build an integrated network of gonadotropin signaling pathways in various tissues. Undoubtedly, research on gonadotropins will continue to provide new knowledge and allow us transcend from benchside to the bedside.

Group V Secretory Phospholipase A2 Is Involved in Tubular Integrity and Sodium Handling in the Kidney

Group V (GV) phospholipase A₂ (PLA₂) is a member of the family of secreted PLA₂ (sPLA2) enzymes_. This enzyme has been identified in several organs, including the kidney. However, the physiologic role of GV sPLA₂ in the maintenance of renal function remains unclear. We used mice lacking the gene encoding GV sPLA₂ (Pla2g5^−/−) and wild-type breeding pairs in the experiments. Mice were individually housed in metabolic cages and 48-h urine was collected for biochemical assays. Kidney samples were evaluated for glomerular morphology, renal fibrosis, and expression/activity of the (Na⁺ + K⁺)-ATPase α1 subunit. We observed that plasma creatinine levels were increased in Pla2g5^−/− mice following by a decrease in creatinine clearance. The levels of urinary protein were higher in Pla2g5^−/− mice than in the control group. Markers of tubular integrity and function such as γ-glutamyl transpeptidase, lactate dehydrogenase, and sodium excretion fraction (FE_Na⁺) were also increased in Pla2g5^−/− mice. The increased FE_Na⁺ observed in Pla2g5^−/− mice was correlated to alterations in cortical (Na⁺ + K⁺) ATPase activity/ expression. In addition, the kidney from Pla2g5^−/− mice showed accumulation of matrix in corticomedullary glomeruli and tubulointerstitial fibrosis. These data suggest GV sPLA₂ is involved in the maintenance of tubular cell function and integrity, promoting sodium retention through increased cortical (Na⁺ + K⁺)-ATPase expression and activity.

Mammalian Genotyping Using Acoustic Droplet Ejection for Enhanced Data Reproducibility, Superior Throughput, and Minimized Cross-Contamination

Genetically engineered animal models are major tools of a drug discovery pipeline because they facilitate understanding of the molecular and biochemical basis of disease. These highly complex models of human disease often require increasingly convoluted genetic analysis. With growing needs for throughput and consistency, we find that traditional aspiration-and-dispense liquid-handling robots no longer have the required speed, quality, or reproducibility.We present an adaptation and installation of an acoustic droplet ejection (ADE) liquid-handling system for ultra-high-throughput screening of genetically engineered models. An ADE system is fully integrated with existing laboratory processes and platforms to facilitate execution of PCR and quantitative PCR (qPCR) reactions. Such a configuration permits interrogation of highly complex genetic models in a variety of backgrounds. Our findings demonstrate that a single ADE system replaces 8-10 traditional liquid-handling robots while increasing quality and reproducibility.We demonstrate significant improvements achieved by transitioning to an ADE device: extremely low detectable cross-contamination in PCR and qPCR despite extensive use, greatly increased data reproducibility (large increases in data quality and Cq consistency), lowered reaction volumes for large cost savings, and nearly a magnitude increase in speed per instrument. We show several comparisons between traditional- and ADE-based pipetting for a qPCR-based workflow.

Obesity genetics in mouse and human: back and forth, and back again

Obesity is a major public health concern. This condition results from a constant and complex interplay between predisposing genes and environmental stimuli. Current attempts to manage obesity have been moderately effective and a better understanding of the etiology of obesity is required for the development of more successful and personalized prevention and treatment options. To that effect, mouse models have been an essential tool in expanding our understanding of obesity, due to the availability of their complete genome sequence, genetically identified and defined strains, various tools for genetic manipulation and the accessibility of target tissues for obesity that are not easily attainable from humans. Our knowledge of monogenic obesity in humans greatly benefited from the mouse obesity genetics field. Genes underlying highly penetrant forms of monogenic obesity are part of the leptin-melanocortin pathway in the hypothalamus. Recently, hypothesis-generating genome-wide association studies for polygenic obesity traits in humans have led to the identification of 119 common gene variants with modest effect, most of them having an unknown function. These discoveries have led to novel animal models and have illuminated new biologic pathways. Integrated mouse-human genetic approaches have firmly established new obesity candidate genes. Innovative strategies recently developed by scientists are described in this review to accelerate the identification of causal genes and deepen our understanding of obesity etiology. An exhaustive dissection of the molecular roots of obesity may ultimately help to tackle the growing obesity epidemic worldwide.

Inducible RNAi system and its application in novel therapeutics

RNA interference (RNAi) was discovered as a cellular defense mechanism more than decade ago. It has been exploited as a powerful tool for genetic manipulation. Characterized with specifically silencing target gene expression, it has great potential application for disease treatment. Currently, there are human clinical trials in progress or planned. Despite the excitement regarding this prominent technology, there are many obstacles and concerns that prevent RNAi from being widely used in the therapeutic field. Among them, the non-spatial and non-temporal control is the most difficult challenge, as well as off-target effects and triggering type I immune responses. Inducible RNAi technology can effectively regulate target genes by inducer-mediated small hairpin RNA expression. Combination with inducible regulation systems this makes RNAi technology more sophisticated and may provide a wider application field. This review discusses approaches of inducible RNAi systems, the potential problem areas and solutions and their therapeutic applications. Given the limitations discussed herein being resolved, we believe that inducible RNAi will be a major therapeutic modality within the next several years.

The humankind genome: from genetic diversity to the origin of human diseases

Genome-wide association studies have failed to establish common variant risk for the majority of common human diseases. The underlying reasons for this failure are explained by recent studies of resequencing and comparison of over 1200 human genomes and 10 000 exomes, together with the delineation of DNA methylation patterns (epigenome) and full characterization of coding and noncoding RNAs (transcriptome) being transcribed. These studies have provided the most comprehensive catalogues of functional elements and genetic variants that are now available for global integrative analysis and experimental validation in prospective cohort studies. With these datasets, researchers will have unparalleled opportunities for the alignment, mining, and testing of hypotheses for the roles of specific genetic variants, including copy number variations, single nucleotide polymorphisms, and indels as the cause of specific phenotypes and diseases. Through the use of next-generation sequencing technologies for genotyping and standardized ontological annotation to systematically analyze the effects of genomic variation on humans and model organism phenotypes, we will be able to find candidate genes and new clues for disease's etiology and treatment. This article describes essential concepts in genetics and genomic technologies as well as the emerging computational framework to comprehensively search websites and platforms available for the analysis and interpretation of genomic data.

Quantitative multispectral analysis following fluorescent tissue transplant for visualization of cell origins, types, and interactions

With the desire to understand the contributions of multiple cellular elements to the development of a complex tissue; such as the numerous cell types that participate in regenerating tissue, tumor formation, or vasculogenesis, we devised a multi-colored cellular transplant model of tumor development in which cell populations originate from different fluorescently colored reporter gene mice and are transplanted, engrafted or injected in and around a developing tumor. These colored cells are then recruited and incorporated into the tumor stroma. In order to quantitatively assess bone marrow derived tumor stromal cells, we transplanted GFP expressing transgenic whole bone marrow into lethally irradiated RFP expressing mice as approved by IACUC. 0ovarian tumors that were orthotopically injected into the transplanted mice were excised 6-8 weeks post engraftment and analyzed for bone marrow marker of origin (GFP) as well as antibody markers to detect tumor associated stroma using multispectral imaging techniques. We then adapted a methodology we call MIMicc- Multispectral Interrogation of Multiplexed cellular compositions, using multispectral unmixing of fluoroprobes to quantitatively assess which labeled cell came from which starting populations (based on original reporter gene labels), and as our ability to unmix 4, 5, 6 or more spectra per slide increases, we've added additional immunohistochemistry associated with cell lineages or differentiation to increase precision. Utilizing software to detect co-localized multiplexed-fluorescent signals, tumor stromal populations can be traced, enumerated and characterized based on marker staining.

A conceptual and practical guide to the behavioural evaluation of animal models of the symptomatology and therapy of schizophrenia

Schizophrenia is a chronic debilitating brain disorder characterized by a complex set of perceptual and behavioural symptoms that severely disrupt and undermine the patient's psychological well-being and quality of life. Since the exact disease mechanisms remain essentially unknown, holistic animal models are indispensable tools for any serious investigation into the neurobiology of schizophrenia, including the search for remedies, prevention of the disease and possible biological markers. This review provides some practical advice to those confronted with the task of evaluating their animal models for relevance to schizophrenia, a task that inevitably involves behavioural tests with animals. To a novice, this challenge not only is a technical one but also entails attention to interpretative issues concerning validity and translational power. Here, we attempt to offer some guidance to help overcome these obstacles by drawing on our experience of diverse animal models of schizophrenia based on genetics, strain difference, brain lesions, pharmacological induction and early life developmental manipulations. The review pays equal emphasis to the general (theoretical) considerations of experimental design and the illustration of the problems related to critical test parameters and the data analysis of selected exemplar behavioural tests. Finally, the individual differences of behavioural expression in relevant tests observed in wild-type animals might offer an alternative approach in order to explore the mechanism of schizophrenia-related behavioural dysfunction at the molecular, cellular and structural levels, all of which are of more immediate relevance to cell and tissue research.

Behavioral testing regimens in genetic-based animal models of Parkinson's disease: cogencies and caveats

Although the onset and progression of Parkinson's disease (PD) is fundamentally sporadic, identification of several of the genes implicated in the disease has provided significant insight concerning patho-physiological mechanisms potentially underlying sporadic PD. Moreover, such studies have caused a revolution in the way researchers view the disease. Since single genes responsible for rare familial forms of the disease have only been identified within the past few years, animal models based on these defects have only recently been generated, thereby not leaving a lot of time for their evaluation and subsequent improvement. The current article provides an extensive review of the major motor and non-motor behavioral tests used in genetically-induced Parkinsonian animals. Moreover, we assess the insights concerning the etiopathogenesis of PD generated from use of such tests and how these have improved available treatment strategies for alleviating aspects of sporadic and non-sporadic parkinsonism.