Improved embryonic stem cell technologies

A dystrophic Duchenne mouse model for testing human antisense oligonucleotides

Duchenne muscular dystrophy (DMD) is a severe muscle-wasting disease generally caused by reading frame disrupting mutations in the DMD gene resulting in loss of functional dystrophin protein. The reading frame can be restored by antisense oligonucleotide (AON)-mediated exon skipping, allowing production of internally deleted, but partially functional dystrophin proteins as found in the less severe Becker muscular dystrophy. Due to genetic variation between species, mouse models with mutations in the murine genes are of limited use to test and further optimize human specific AONs in vivo. To address this we have generated the del52hDMD/mdx mouse. This model carries both murine and human DMD genes. However, mouse dystrophin expression is abolished due to a stop mutation in exon 23, while the expression of human dystrophin is abolished due to a deletion of exon 52. The del52hDMD/mdx model, like mdx, shows signs of muscle dystrophy on a histological level and phenotypically mild functional impairment. Local administration of human specific vivo morpholinos induces exon skipping and dystrophin restoration in these mice. Depending on the number of mismatches, occasional skipping of the murine Dmd gene, albeit at low levels, could be observed. Unlike previous models, the del52hDMD/mdx model enables the in vivo analysis of human specific AONs targeting exon 51 or exon 53 on RNA and protein level and muscle quality and function. Therefore, it will be a valuable tool for optimizing human specific AONs and genome editing approaches for DMD.

Generation of embryonic stem cells and mice for duchenne research

Duchenne muscular dystrophy (DMD) is a muscle-wasting disease in which muscle is continuously damaged, resulting in loss of muscle tissue and function. Antisense-mediated exon skipping is a promising therapeutic approach for DMD. This method uses sequence specific antisense oligonucleotides (AONs) to reframe disrupted dystrophin transcripts. As AONs function in a sequence specific manner, human specific AONs cannot be tested in the mdx mouse, which carries a mutation in the murine Dmd gene. We have previously generated a mouse model carrying the complete human DMD gene (hDMD mouse) integrated in the mouse genome to overcome this problem. However, as this is not a disease model, it cannot be used to study the effect of AON treatment on protein level and muscle function. Therefore, our long term goal is to generate deletions in the human DMD gene in a mouse carrying the hDMD gene in an mdx background. Towards this aim, we generated a male ES cell line carrying the hDMD gene while having the mdx point mutation. Inheritance of the hDMD gene by the ES cell was confirmed both on DNA and mRNA level. Quality control of the ES cells revealed that the pluripotency marker genes Oct-4 and Nanog are well expressed and that 85% of cells have 40 chromosomes. Germ line competence of this cell line has been confirmed, and 2 mice strains were derived from this cell line and crossed back on a C57BL6 background: hDMD/mdx and mdx(BL6).

Efficient division and sampling of cell colonies using microcup arrays

A microengineered array to sample clonal colonies is described. The cells were cultured on an array of individually releasable elements until the colonies expanded to cover multiple elements. Single elements were released using a laser-based system and collected to sample cells from individual colonies. A greater than an 85% rate in splitting and collecting colonies was achieved using a 3-dimensional cup-like design or "microcup". Surface modification using patterned titanium deposition of the glass substrate improved the stability of microcup adhesion to the glass while enabling minimization of the laser energy for splitting the colonies. Smaller microcup dimensions and slotting the microcup walls reduced the time needed for colonies to expand into multiple microcups. The stem cell colony retained on the array and the collected fraction within released microcups remained undifferentiated and viable. The colony samples were characterized by both reporter gene expression and a destructive assay (PCR) to identify target colonies. The platform is envisioned as a means to rapidly establish cell lines using a destructive assay to identify desired clones.

Fluorescent transgenic mice suitable for multi-color aggregation chimera studies

We recently reported a novel method of mouse transgenesis called Pronuclear Injection-based Targeted Transgenisis (PITT) using which a series of fluorescent transgenic (Tg) mice lines were generated. These lines, unlike those generated using conventional random integration methods, express the transgenes faithfully and reproducibly generation after generation. Because of this superior nature, these lines are ideal for the generation of multi-colored aggregation chimeras that can be used to study cell-cell interactions and lineage analyses in living embryos/organs, where the transgenes can be detected and the clonal origin of a given cell population easily traced by its distinct fluorescence. In this study, to verify if Tg fluorescent mice generated through PITT were suitable for such applications, we sought to generate chimeric blastocysts and chimeric-Tg mice by aggregating two- or three-colored 8-cell embryos. Our analyses using these models led to the following observations. First, we noticed that cell mixing was infrequent during the stages of morula to early blastocyst. Second, chimeric fetuses obtained after aggregation of the two-colored 8-cell embryos exhibited uniform cell mixing. And third, in the organs of adult chimeric mice, the mode of cell distribution could be either clonal or polyclonal, as previously pointed out by others. Implications of our novel and improved Tg-chimeric mice approach for clonal cell lineage and developmental studies are discussed.

Mouse models to study kidney development, function and disease

PURPOSE OF REVIEW

The mouse is the most widely used model organism to study gene function in the kidney in vivo. Here we review recent advances in technologies to manipulate the mouse genome and gene function to study renal biology. We discuss strengths and weaknesses of the approaches and provide examples in which they have been used to address renal questions. In addition, we provide a summary of the available resources of mouse tools and gene-targeting consortia.

RECENT FINDINGS

Although conventional gene-targeting and spontaneous genetic mutations in mice have provided great insights into kidney function over several decades, the addition of powerful renal-specific gene-targeting tools and the advent of RNA technologies to manipulate gene function in vivo allow investigators to address research questions more precisely in the laboratory. Together with the establishment of multiple international consortia to target all the genes in the mouse genome and the development of gene trap and N-ethyl-N-nitrosourea resources, genetic manipulation in mice has become more efficient.

SUMMARY

The availability of newer technologies and tremendous resources for mouse strains and reagents ensures that the mouse will remain a key model organism to study renal function.

Functional phenotyping of the maternal albumin turnover in the mouse placenta by dynamic contrast-enhanced MRI

Purpose

The purpose of this study was to develop a tool for functional phenotyping of the maternal circulation in the mouse placenta.

Procedures

In utero macromolecular dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was performed on embryonic day 10.5 (E10.5), E13.5, and E18.5. Fluorescence analysis was also used for validation of the results.

Results

The initial rate of contrast enhancement revealed an increased maternal blood volume fraction as the pregnancy progressed. Serial imaging of E10.5 and E13.5 placentas revealed a loss of contrast enhancement due to phagocytic uptake. A key application of macromolecular DCE-MRI would be to follow mouse pregnancies during fetal and placental manipulation including embryo transfer, tetraploid complementation, and fetal resorptions. We were able to resolve strain differences in ICR outbred mice carrying both ICR and C57Bl/6J embryos and to differentiate in utero resorptions from functional placentas.

Conclusions

Our results highlight the importance of the functional in utero analysis of placental vascularization in physiological phenotyping of transgenic mice and suggest MRI, particularly macromolecular DCE-MRI, as a non-invasive tool for the analysis of the placenta.

The construction of transgenic and gene knockout/knockin mouse models of human disease

The genetic and physiological similarities between mice and humans have focused considerable attention on rodents as potential models of human health and disease. Together with the wealth of resources, knowledge, and technologies surrounding the mouse as a model system, these similarities have propelled this species to the forefront of biomedical research. The advent of genomic manipulation has quickly led to the creation and use of genetically engineered mice as powerful tools for cutting edge studies of human disease research including the discovery, refinement, and utility of many currently available therapeutic regimes. In particular, the creation of genetically modified mice as models of human disease has remarkably changed our ability to understand the molecular mechanisms and cellular pathways underlying disease states. Moreover, the mouse models resulting from gene transfer technologies have been important components correlating an individual's gene expression profile to the development of disease pathologies. The objective of this review is to provide physician-scientists with an expansive historical and logistical overview of the creation of mouse models of human disease through gene transfer technologies. Our expectation is that this will facilitate on-going disease research studies and may initiate new areas of translational research leading to enhanced patient care.

Survival and size are differentially regulated by placental and fetal PKBalpha/AKT1 in mice

The importance of placental circulation is exemplified by the correlation of placental size and blood flow with fetal weight and survival during normal and compromised human pregnancies in such conditions as preeclampsia and intrauterine growth restriction (IUGR). Using noninvasive magnetic resonance imaging, we evaluated the role of PKBalpha/AKT1, a major mediator of angiogenesis, on placental vascular function. PKBalpha/AKT1 deficiency reduced maternal blood volume fraction without affecting the integrity of the fetomaternal blood barrier. In addition to angiogenesis, PKBalpha/AKT1 regulates additional processes related to survival and growth. In accordance with reports in adult mice, we demonstrated a role for PKBalpha/AKT1 in regulating chondrocyte organization in fetal long bones. Using tetraploid complementation experiments with PKBalpha/AKT1-expressing placentas, we found that although placental PKBalpha/AKT1 restored fetal survival, fetal PKBalpha/AKT1 regulated fetal size, because tetraploid complementation did not prevent intrauterine growth retardation. Histological examination of rescued fetuses showed reduced liver blood vessel and renal glomeruli capillary density in PKBalpha/Akt1 null fetuses, both of which were restored by tetraploid complementation. However, bone development was still impaired in tetraploid-rescued PKBalpha/Akt1 null fetuses. Although PKBalpha/AKT1-expressing placentas restored chondrocyte cell number in the hypertrophic layer of humeri, fetal PKBalpha/AKT1 was found to be necessary for chondrocyte columnar organization. Remarkably, a dose-dependent phenotype was exhibited for PKBalpha/AKT1 when examining PKBalpha/Akt1 heterozygous fetuses as well as those complemented by tetraploid placentas. The differential role of PKBalpha/AKT1 on mouse fetal survival and growth may shed light on its roles in human IUGR.

New approaches for modelling sporadic genetic disease in the mouse

Sporadic diseases, which occur as single, scattered cases, are among the commonest causes of human morbidity and death. They result in a variety of diseases, including many cancers, premature aging, neurodegeneration and skeletal defects. They are often pathogenetically complex, involving a mosaic distribution of affected cells, and are difficult to model in the mouse. Faithful models of sporadic diseases require innovative forms of genetic manipulation to accurately recreate their initiation and pathogenesis. Such modelling is crucial to understanding these diseases and, by extension, to the development of therapeutic approaches to treat them. This article focuses on sporadic diseases with a genetic aetiology, the challenges they pose to biomedical researchers, and the different current and developing approaches used to model such disorders in the mouse.

Sorting and expansion of murine embryonic stem cell colonies using micropallet arrays

Isolation of cell colonies is an essential task in most stem cell studies. Conventional techniques for colony selection and isolation require significant time, labor, and consumption of expensive reagents. New microengineered technologies hold the promise for improving colony manipulation by reducing the required manpower and reagent consumption. Murine embryonic stem cells were cultured on arrays composed of releasable elements termed micropallets created from a biocompatible photoresist. Micropallets containing undifferentiated colonies were released using a laser-based technique followed by cell collection and expansion in culture. The micropallet arrays provided a biocompatible substrate for maintaining undifferentiated murine stem cells in culture. A surface coating of 0.025% gelatin was shown to be optimal for cell culture and collection. Arrays composed of surface-roughened micropallets provided further improvements in culture and isolation. Colonies of viable stem cells were efficiently isolated and collected. Colonies sorted in this manner were shown to remain undifferentiated even after collection and further expansion in culture. Qualitative and quantitative analyses of sorting, collection efficiency, and cell viability after release and expansion of stem cell colonies demonstrated that the micropallet array technology is a promising alternative to conventional sorting methods for stem cell applications.

Aggregation chimeras: combining ES cells, diploid, and tetraploid embryos

During the past 40 years, mouse chimeras have served as invaluable tools for studying not only genetics but also embryonic development, and the path from undifferentiated cell populations to fully committed functional cell types. This chapter gives a description of the early events of cell commitment and differentiation in the pre-and postimplantation-stage embryo. Next, a discussion follows highlighting the most commonly used as well as more recently developed applications of various cell types and origins used in the production of chimeras. Finally, detailed protocols and trouble-shooting suggestions will be presented for each of the steps involved.