Targeted insertion of conditional expression cassettes into the mouse genome using the modified i-PITT.

BACKGROUND: Transgenic (Tg) mice are widely used in biomedical research, and they are typically generated by injecting transgenic DNA cassettes into pronuclei of one-cell stage zygotes. Such animals often show unreliable expression of the transgenic DNA, one of the major reasons for which is random insertion of the transgenes. We previously developed a method called "pronuclear injection-based targeted transgenesis" (PITT), in which DNA constructs are directed to insert at pre-designated genomic loci. PITT was achieved by pre-installing so called landing pad sequences (such as heterotypic LoxP sites or attP sites) to create seed mice and then injecting Cre recombinase or PhiC31 integrase mRNAs along with a compatible donor plasmid into zygotes derived from the seed mice. PITT and its subsequent version, improved PITT (i-PITT), overcome disadvantages of conventional Tg mice such as lack of consistent and reliable expression of the cassettes among different Tg mouse lines, and the PITT approach is superior in terms of cost and labor. One of the limitations of PITT, particularly using Cre-mRNA, is that the approach cannot be used for insertion of conditional expression cassettes using Cre-LoxP site-specific recombination. This is because the LoxP sites in the donor plasmids intended for achieving conditional expression of the transgene will interfere with the PITT recombination reaction with LoxP sites in the landing pad. RESULTS: To enable the i-PITT method to insert a conditional expression cassette, we modified the approach by simultaneously using PhiC31o and FLPo mRNAs. We demonstrate the strategy by creating a model containing a conditional expression cassette at the Rosa26 locus with an efficiency of 13.7%. We also demonstrate that inclusion of FLPo mRNA excludes the insertion of vector backbones in the founder mice. CONCLUSIONS: Simultaneous use of PhiC31 and FLP in i-PITT approach allows insertion of donor plasmids containing Cre-loxP-based conditional expression cassettes.

Influence of Heterologous Transplant of DNA-lacking Mitochondria from Entamoeba histolytica on Proliferation of Entamoeba invadens.

In mitochondria, compatibility of proteins encoded in mitochondrial DNA and nuclear DNA is essential for the normal functioning of the organelle. Incompatibility between mitochondrial and nuclear DNA can lead to dysfunctional respiration, mitochondrial diseases, and lethal problems, which suggests that the presence of heterologous mitochondria is unfavorable. In a previous study, we established a transplant method for DNA-lacking mitochondria (mitosomes) in the anaerobic protozoan Entamoeba histolytica. In this study, interspecies transplant of mitosomes from E. histolytica into Entamoeba invadens, which is a parasitic protozoon of reptiles, was performed using the microinjection method at various temperatures and injection volumes. When E. invadens was used as recipient, it showed higher tolerance to a lower temperature and larger injection volume, in comparison with E. histolytica. After microinjection, donor mitosomes expressing HA-tag conjugated protein were observed in recipient cells by immunofluorescent staining. The heterologous mitosomes-injected cells proliferated and growth rate of the microinjected-cells was similar to that of intact cells. Therefore, we conclude that interspecies transplant of DNA-lacking mitochondria does not result in incompatibility.

Conditional knockout of Foxc2 gene in kidney: efficient generation of conditional alleles of single-exon gene by double-selection system.

Foxc2 is a single-exon gene and a key regulator in development of multiple organs, including kidney. To avoid embryonic lethality of conventional Foxc2 knockout mice, we conditionally deleted Foxc2 in kidneys. Conditional targeting of a single-exon gene involves the large floxed gene segment spanning from promoter region to coding region to avoid functional disruption of the gene by the insertion of a loxP site. Therefore, in ES cell clones surviving a conventional single-selection, e.g., neomycin-resistant gene (neo) alone, homologous recombination between the long floxed segment and target genome results in a high incidence of having only one loxP site adjacent to the selection marker. To avoid this limitation, we employed a double-selection system. We generated a Foxc2 targeting construct in which a floxed segment contained 4.6 kb mouse genome and two different selection marker genes, zeocin-resistant gene and neo, that were placed adjacent to each loxP site. After double-selection by zeocin and neomycin, 72 surviving clones were screened that yielded three correctly targeted clones. After floxed Foxc2 mice were generated by tetraploid complementation, we removed the two selection marker genes by a simultaneous-single microinjection of expression vectors for Dre and Flp recombinases into in vitro-fertilized eggs. To delete Foxc2 in mouse kidneys, floxed Foxc2 mice were mated with Pax2-Cre mice. Newborn Pax2-Cre; Foxc2(loxP/loxP) mice showed kidney hypoplasia and glomerular cysts. These results indicate the feasibility of generating floxed Foxc2 mice by double-selection system and simultaneous removal of selection markers with a single microinjection.

Diphenyl-tetrazol-propanamide Derivatives Act as Dual-Specific Antagonists of Platelet CLEC-2 and Glycoprotein VI.

BACKGROUND: Platelet C-type lectin-like receptor 2 (CLEC-2) induces platelet activation and aggregation after clustering by its ligand podoplanin (PDPN). PDPN, which is not normally expressed in cells in contact with blood flow, is induced in inflammatory immune cells and some malignant tumor cells, thereby increasing the risk of venous thromboembolism (VTE) and tumor metastasis. Therefore, small-molecule compounds that can interfere with the PDPN-CLEC-2 axis have the potential to become selective antiplatelet agents. METHODS AND RESULTS: Using molecular docking analysis of CLEC-2 and a PDPN-CLEC-2 binding-inhibition assay, we identified a group of diphenyl-tetrazol-propanamide derivatives as novel CLEC-2 inhibitors. A total of 12 hit compounds also inhibited PDPN-induced platelet aggregation in humans and mice. Unexpectedly, these compounds also fit the collagen-binding pocket of the glycoprotein VI molecule, thereby inhibiting collagen interaction. These compounds also inhibited collagen-induced platelet aggregation, and one compound ameliorated collagen-induced thrombocytopenia in mice. For clinical use, these compounds will require a degree of chemical modification to decrease albumin binding. CONCLUSION: Nonetheless, as dual activation of platelets by collagen and PDPN-positive cells is expected to occur after the rupture of atherosclerotic plaques, these dual antagonists could represent a promising pharmacophore, particularly for arterial thrombosis, in addition to VTE and metastasis.

Pronuclear injection-based mouse targeted transgenesis for reproducible and highly efficient transgene expression.

Mouse transgenesis has proven invaluable for analysis of gene function and generation of human disease models. We describe here the development of a pronuclear injection-based targeted transgenesis (PITT) system, involving site-specific integration in fertilized eggs. The system was applied to two different genomic target loci to generate a series of transgenic lines including fluorescent mice, which reproducibly displayed strong, ubiquitous and stable transgene expression. We also demonstrated that knockdown mice could be readily generated by PITT by taking advantage of the reproducible and highly efficient expression system. The PITT system, which circumvents the problem of unpredictable and unstable transgene expression of conventional random-integration transgenic mice, reduces the time, cost and effort needed to generate transgenic mice, and is potentially applicable to both in vivo 'gain-of-function' and 'loss-of-function' studies.

Monitoring the autophagy-endolysosomal system using monomeric Keima-fused MAP1LC3B.

The autophagy-endolysosomal pathway is an evolutionally conserved degradation system that is tightly linked to a wide variety of physiological processes. Dysfunction of this system is associated with many pathological conditions such as cancer, inflammation and neurodegenerative diseases. Therefore, monitoring the cellular autophagy-endolysosomal activity is crucial for studies on the pathogenesis as well as therapeutics of such disorders. To this end, we here sought to create a novel means exploiting Keima, an acid-stable fluorescent protein possessing pH-dependent fluorescence excitation spectra, for precisely monitoring the autophagy-endolysosomal system. First, we generated three lines of transgenic (tg) mouse expressing monomeric Keima-fused MAP1LC3B (mKeima-LC3B). Then, these tg mice were subjected to starvation by food-restriction, and also challenged to neurodegeneration by genetically crossing with a mouse model of amyotrophic lateral sclerosis; i.e., SOD1H46R transgenic mouse. Unexpectedly, despite that a lipidated-form of endogenous LC3 (LC3-II) was significantly increased, those of mKeima-LC3B (mKeima-LC3B-II) were not changed under both stressed conditions. It was also noted that mKeima-LC3B-positive aggregates were progressively accumulated in the spinal cord of SOD1H46R;mKeima-LC3B double-tg mice, suggestive of acid-resistance and aggregate-prone natures of long-term overexpressed mKeima-LC3B in vivo. Next, we characterized mouse embryonic fibroblasts (MEFs) derived from mKeima-LC3B-tg mice. In contrast with in vivo, levels of mKeima-LC3B-I were decreased under starved conditions. Furthermore, when starved MEFs were treated with chloroquine (CQ), the abundance of mKeima-LC3B-II was significantly increased. Remarkably, when cultured medium was repeatedly changed between DMEM (nutrient-rich) and EBSS (starvation), acidic/neutral signal ratios of mKeima-LC3B-positive compartments were rapidly and reversibly shifted, which were suppressed by the CQ treatment, indicating that intraluminal pH of mKeima-LC3B-positive vesicles was changeable upon nutritional conditions of culture media. Taken together, although mKeima-LC3B-tg mice may not be an appropriate tool to monitor the autophagy-endolysosomal system in vivo, mKeima-LC3B must be one of the most sensitive reporter molecules for monitoring this system under in vitro cultured conditions.

Creation of CRISPR-based germline-genome-engineered mice without ex vivo handling of zygotes by i-GONAD.

Methods to create genetically engineered mice involve three major steps: harvesting embryos from one set of females, microinjection of reagents into embryos ex vivo and their surgical transfer to another set of females. Although tedious, these methods have been used for more than three decades to create mouse models. We recently developed a method named GONAD (genome editing via oviductal nucleic acids delivery), which bypasses these steps. GONAD involves injection of CRISPR components (Cas9 mRNA and guide RNA (gRNA)) into the oviducts of pregnant females 1.5 d post conception, followed by in vivo electroporation to deliver the components into the zygotes in situ. Using GONAD, we demonstrated that target genes can be disrupted and analyzed at different stages of mouse embryonic development. Subsequently, we developed improved GONAD (i-GONAD) by delivering CRISPR ribonucleoproteins (RNPs; Cas9 protein or Cpf1 protein and gRNA) into day-0.7 pregnant mice, which made it suitable for routine generation of knockout and large-deletion mouse models. i-GONAD can also generate knock-in models containing up to 1-kb inserts when single-stranded DNA (ssDNA) repair templates are supplied. i-GONAD offers other advantages: it does not require vasectomized males and pseudo-pregnant females, the females used for i-GONAD are not sacrificed and can be used for other experiments, it can be easily adopted in laboratories lacking sophisticated microinjection equipment, and can be implemented by researchers skilled in small-animal surgery but lacking embryo-handling skills. Here, we provide a step-by-step protocol for establishing the i-GONAD method. The protocol takes ∼6 weeks to generate the founder mice.

Behavior of DNA-lacking mitochondria in Entamoeba histolytica revealed by organelle transplant.

The anaerobic protozoan parasite Entamoeba histolytica has mitosomes that are mitochondria lacking some canonical functions and organelle DNA. Mitosomes play an important role in the life cycle of the parasite. The distribution of proteins in mitosomes is not uniform, and how mitosomes are maintained and retained is unknown. To answer these questions, we developed a transplant method for mitosomes with hemagglutinin-tagged protein into recipient cells containing mitosomes with Myc-tagged protein. Immunofluorescence staining showed that the two protein tags colocalized in single mitosomes in some recipient cells. These results suggest that our transplant method can be used in anaerobic protozoa and that donor mitosomes may obtain recipient proteins through fusion with other mitosomes or through de novo synthesis of proteins in recipient cells.

A transposon-based chromosomal engineering method to survey a large cis-regulatory landscape in mice.

A large cis-regulatory landscape is a common feature of vertebrate genomes, particularly at key developmental gene loci with finely tuned expression patterns. Existing genetic tools for surveying large genomic regions of interest spanning over hundreds of kilobases are limited. Here we propose a chromosomal engineering strategy exploiting the local hopping trait of the Sleeping Beauty transposon in the mouse genome. We generated embryonic stem cells with a targeted integration of the transposon vector, carrying an enhancer-detecting lacZ reporter and loxP cassette, into the developmentally critical Pax1 gene locus, followed by efficient local transpositions, nested deletion formation and derivation of embryos by tetraploid complementation. Comparative reporter expression analysis among different insertion/deletion embryos substantially facilitated long-range cis-regulatory element mapping in the genomic neighborhood and demonstrated the potential of the transposon-based approach as a versatile tool for exploration of defined genomic intervals of functional or clinical relevance, such as disease-associated microdeletions.