Gene Targeting Methods Research Articles

Functionality of In vitro Reconstituted Group II Intron RmInt1-Derived Ribonucleoprotein Particles.

The functional unit of mobile group II introns is a ribonucleoprotein particle (RNP) consisting of the intron-encoded protein (IEP) and the excised intron RNA. The IEP has reverse transcriptase activity but also promotes RNA splicing, and the RNA-protein complex triggers site-specific DNA insertion by reverse splicing, in a process called retrohoming. In vitro reconstituted ribonucleoprotein complexes from the Lactococcus lactis group II intron Ll.LtrB, which produce a double strand break, have recently been studied as a means of developing group II intron-based gene targeting methods for higher organisms. The Sinorhizobium meliloti group II intron RmInt1 is an efficient mobile retroelement, the dispersal of which appears to be linked to transient single-stranded DNA during replication. The RmInt1IEP lacks the endonuclease domain (En) and cannot cut the bottom strand to generate the 3′ end to initiate reverse transcription. We used an Escherichia coli expression system to produce soluble and active RmInt1 IEP and reconstituted RNPs with purified components in vitro. The RNPs generated were functional and reverse-spliced into a single-stranded DNA target. This work constitutes the starting point for the use of group II introns lacking DNA endonuclease domain-derived RNPs for highly specific gene targeting methods.

A trait stacking system via intra-genomic homologous recombination

A gene targeting method has been developed, which allows the conversion of 'breeding stacks', containing unlinked transgenes into a 'molecular stack' and thereby circumventing the breeding challenges associated with transgene segregation. A gene targeting method has been developed for converting two unlinked trait loci into a single locus transgene stack. The method utilizes intra-genomic homologous recombination (IGHR) between stably integrated target and donor loci which share sequence homology and nuclease cleavage sites whereby the donor contains a promoterless herbicide resistance transgene. Upon crossing with a zinc finger nuclease (ZFN)-expressing plant, double-strand breaks (DSB) are created in both the stably integrated target and donor loci. DSBs flanking the donor locus result in intra-genomic mobilization of a promoterless selectable marker-containing donor sequence, which can be utilized as a template for homology-directed repair of a concomitant DSB at the target locus resulting in a functional selectable marker via nuclease-mediated cassette exchange (NMCE). The method was successfully demonstrated in maize using a glyphosate tolerance gene as a donor whereby up to 3.3% of the resulting progeny embryos cultured on selection medium regenerated plants with the donor sequence integrated into the target locus. The process could be extended to multiple cycles of trait stacking by virtue of a unique intron sequence homology for NMCE between the target and the donor loci. This is the first report that describes NMCE via IGHR, thereby enabling trait stacking using conventional crossing.

Developing a de novo targeted knock-in method based on in utero electroporation into the mammalian brain.

Genome-editing technology has revolutionized the field of biology. Here, we report a novel de novo gene-targeting method mediated by in utero electroporation into the developing mammalian brain. Electroporation of donor DNA with the CRISPR/Cas9 system vectors successfully leads to knock-in of the donor sequence, such as EGFP, to the target site via the homology-directed repair mechanism. We developed a targeting vector system optimized to prevent anomalous leaky expression of the donor gene from the plasmid, which otherwise often occurs depending on the donor sequence. The knock-in efficiency of the electroporated progenitors reached up to 40% in the early stage and 20% in the late stage of the developing mouse brain. Furthermore, we inserted different fluorescent markers into the target gene in each homologous chromosome, successfully distinguishing homozygous knock-in cells by color. We also applied this de novo gene targeting to the ferret model for the study of complex mammalian brains. Our results demonstrate that this technique is widely applicable for monitoring gene expression, visualizing protein localization, lineage analysis and gene knockout, all at the single-cell level, in developmental tissues.

RAC-tagging: Recombineering And Cas9-assisted targeting for protein tagging and conditional analyses.

A fluent method for gene targeting to establish protein tagged and ligand inducible conditional loss-of-function alleles is described. We couple new recombineering applications for one-step cloning of gRNA oligonucleotides and rapid generation of short-arm (~1 kb) targeting constructs with the power of Cas9-assisted targeting to establish protein tagged alleles in embryonic stem cells at high efficiency. RAC (Recombineering And Cas9)-tagging with Venus, BirM, APEX2 and the auxin degron is facilitated by a recombineering-ready plasmid series that permits the reuse of gene-specific reagents to insert different tags. Here we focus on protein tagging with the auxin degron because it is a ligand-regulated loss-of-function strategy that is rapid and reversible. Furthermore it includes the additional challenge of biallelic targeting. Despite high frequencies of monoallelic RAC-targeting, we found that simultaneous biallelic targeting benefits from long-arm (>4 kb) targeting constructs. Consequently an updated recombineering pipeline for fluent generation of long arm targeting constructs is also presented.

Genome Engineering with TALE and CRISPR Systems in Neuroscience.

Recent advancement in genome engineering technology is changing the landscape of biological research and providing neuroscientists with an opportunity to develop new methodologies to ask critical research questions. This advancement is highlighted by the increased use of programmable DNA-binding agents (PDBAs) such as transcription activator-like effector (TALE) and RNA-guided clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR associated (Cas) systems. These PDBAs fused or co-expressed with various effector domains allow precise modification of genomic sequences and gene expression levels. These technologies mirror and extend beyond classic gene targeting methods contributing to the development of novel tools for basic and clinical neuroscience. In this Review, we discuss the recent development in genome engineering and potential applications of this technology in the field of neuroscience.

Targeted mutagenesis in chicken using CRISPR/Cas9 system.

The CRISPR/Cas9 system is a simple and powerful tool for genome editing in various organisms including livestock animals. However, the system has not been applied to poultry because of the difficulty in accessing their zygotes. Here we report the implementation of CRISPR/Cas9-mediated gene targeting in chickens. Two egg white genes, ovalbumin and ovomucoid, were efficiently (>90%) mutagenized in cultured chicken primordial germ cells (PGCs) by transfection of circular plasmids encoding Cas9, a single guide RNA, and a gene encoding drug resistance, followed by transient antibiotic selection. We transplanted CRISPR-induced mutant-ovomucoid PGCs into recipient chicken embryos and established three germline chimeric roosters (G0). All of the roosters had donor-derived mutant-ovomucoid spermatozoa, and the two with a high transmission rate of donor-derived gametes produced heterozygous mutant ovomucoid chickens as about half of their donor-derived offspring in the next generation (G1). Furthermore, we generated ovomucoid homozygous mutant offspring (G2) by crossing the G1 mutant chickens. Taken together, these results demonstrate that the CRISPR/Cas9 system is a simple and effective gene-targeting method in chickens.

Construction of a gene knockout CHO cell line using a simple gene targeting method

Background Therapeutic antibodies have become an important focus of the biopharmaceutical industry. The Chinese hamster ovary (CHO) cell line is a major host for therapeutic antibody production. To construct productive CHO cell lines, two major transfection methods are commonly used, i.e., random integration and gene targeting. Random integration is a common method in which randomly integrated transgenes cause variation in antibody productivity because they are located in various chromosomal regions that affect transgene expression levels. Recently, gene-targeting methods, in which exogenous genes are inserted into a specific chromosomal region, have improved remarkably. Gene targeting is based on homologous recombination using sequences targeting a specific genomic region of the host cell. Homologous sequences located on both sides of the exogenous gene are used. We used the recently developed clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated proteins (Cas9) system as a gene-targeting method. The CRISPR-Cas9 system induces double-strand breaks (DSBs) via guide RNA and Cas9, which increases the efficiency of homologous recombination [1]. Guide RNA hybridizes to a target integration site and induces Cas9 protein expression, leading to DSB. Finally, the Cas9 protein cuts genomic DNA. In this study, we constructed a simple genetargeting method in CHO cells using the CRISPR-Cas9 system in which CRISPR vectors induce DSBs and genetargeting vectors are inserted at the DSB site. In the conventional method, gene-targeting vectors should contain homology arms for effective recombination. In this study, we used the CRISPER system without homology arms for gene-targeted recombination. Materials and methods We constructed a CRISPR-Cas9 vector that expresses a guide RNA sequence targeting a region on chromosome O. Chromosome O was selected based on a previous classification of gene-amplified CHO cell chromosomes in order of decreasing size and assigned letters from A to T by fluorescence in situ hybridization (FISH) [2]. The CRISPR targeting sequence was determined from the BAC clone Cg0031N14, which contained the chromosome O sequence. Gene targeting vectors (pcDNA-GFP-DHFR) with or without target site homology arms were constructed from BAC clone Cg0031N14. The percentage of exogenous gene integration into chromosome O was determined by a FISH analysis. Total RNA extracted from E14Tg2a (mouse ES cells) was kindly provided by Dr. Tohru Kimura, Kitasato University, Kanagawa, Japan.

In vitro gene manipulation of spinal muscular atrophy fibroblast cell line using gene-targeting fragment for restoration of SMN protein expression.

The reduced level of survival motor neuron (SMN) protein, caused by homozygous deletions in the SMN gene, led to a common neurodegenerative disorder known as spinal muscular atrophy (SMA). In spite of extensive efforts to find a cure for SMA, there is currently no effective treatment available for this devastating disease. In this study, restoration of SMN expression through 'gene-targeting' method in SMA fibroblast cells was attempted. We designed a 2697-bp gene-targeting cassette; it consisted of an SMN1 open reading frame expressing 38 kD SMN protein and the upstream and downstream regions of exon 1 of SMN1 gene at the ends as the homology arms. SMA fibroblast cells were transfected by gene-targeting cassette using Lipofectamine LTX-PLUS reagent. Occurrence of homologous recombination in selected cells was investigated by PCR analysis. Increased expression of SMN protein was shown by real-time PCR and western blotting analysis. The immunofluorescence analysis results demonstrated that the number of SMN nuclear structures, Gems, was the same as or greater than the number of Gems found in normal fibroblasts. The results of this study indicate that gene-targeting methods do, in fact, present as an alternative for restoration of SMN expression in SMA patients-derived cells in vitro.

Accidents and Damage Control

My work uncovering the eukaryotic DNA damage response pathway is a tale of serendipity and four amino acids. After graduate school at MIT, I joined Ron Davis’s lab as a post-doc initially to work on plants but became interested in developing gene-targeting methods for mammals. I had reasoned, naively, that the protein responsible for homologous recombination in mammals would be related to the master regulator of recombination in bacteria, recA. RecA protein had the ability to initiate recombination in vitro on its own using ssDNA and ATP.

563. Rapid and Nuclease-Free Generation of Gene-Repaired Human iPS Cells from IL2RG-Defective Fibroblasts

Recent developments of artificial nucleases, such as TALENs and CRISPR/Cas9, have made gene repair therapy of inherited diseases more realistic. However, off-target chromosomal breaks resulting in imprecise DNA repair by the nucleases are still significant concerns from safety aspects, which is the most critical issue of clinical gene therapy. Furthermore, prolonged culture during induction and manipulation of induced pluripotent stem cells (iPSCs) has been shown to increase point mutations and copy number variations in the iPSC genome, raising additional safety concerns for therapeutic applications of iPSCs. In order to minimize cell culture for iPSC induction and achieve efficient gene repair without using nucleases, we examined a strategy of consecutive iPSC induction and gene repair without cell cloning between the two processes. For this purpose, we utilized Sendai virus vector (SeV)-mediated iPSC induction and helper-dependent adenoviral vector (HDAdV)-mediated gene targeting.To mimic somatic cells from patients of X-linked severe combined immunodeficiency, we firstly knocked out exon 1 of the common gamma chain of human interleukin-2 receptor (IL2RG) locus by utilizing TALENs, and subsequently derived fibroblast-like cells. Next, these cells were subject to iPSC induction by using the SeV expressing Yamanaka factors, SeVdp(KOSM). Instead of isolating and characterizing individual SeV-iPS colonies before gene targeting, iPSC-like colonies were grown as a cell population. Twenty-two to 26 days after SeV infection, the cells were transduced with a HDAdV targeting the IL2RG locus. This HDAdV was designed to introduce the PGK-neo cassette into intron 4 and to repair the mutation of exon 1. Cells were subject to G418/FIAU selection to isolate gene-targeted SeV-iPS colonies. Correct targeting at the IL2RG locus by the vector in G418/FIAU double-resistant colonies was verified by PCR analyses. From two independent experiments, the gene targeting frequencies were similar to those in authentic human iPSCs at 1.6 – 1.8 × 10-5 per cell and 60 – 75% of chromosomal integration (G418/FIAU-resistance), among them 60 – 80% of gene-targeted colonies had the exon 1 mutation repaired. At the time of HDAdV infection, the SeV-iPSCs already showed characteristics of pluripotency, revealed by bisulfite sequencing of the NANOG locus and TRA-1-60 immunostaining. The pluripotency was also maintained in gene-targeted iPSC colonies. From the start of iPSC induction (infection with SeV) to isolation of gene-repaired iPSC colonies, it took only 40 days. We are currently analyzing the expression of IL2RG in differentiated T cells derived from the gene-repaired iPSCs.These results suggest that, by combining efficient methods for iPSC induction and gene targeting, gene repair therapy using patients’ somatic cells becomes more realistic.

683. In Vivo Expansion of Hepatocytes with Targeted rAAV Integration Results in a >100-Fold Increase of Transgene Expression

The recent development of promoter-less transgene integration technology using 2A fusions promises enhanced safety over traditional gene therapies. These vectors target therapeutic transgenes to loci for highly expressed endogenous genes through homologous recombination. Due to the inherent low frequency of targeted integrations, transgene expression is limited and requires high vector doses. Here we describe a modified 2A fusion integration vector that facilitates in vivo selection and expansion of gene-targeted hepatocytes. In mice treated with this vector, factor IX transgene expression increased over 400-fold during selection.Selection was achieved by incorporating into the integration vector a genetic element that rescues gene-targeted hepatocytes from induced hepatotoxic conditions. Blocking Fah (fumarylacetoacetate hydrolase) leads to hepatotoxic accumulation of the enzyme's substrate fumarylacetoacetate (FAA). This toxicity can be rescued by inhibiting Hpd, an enzyme upstream of Fah. In Fah-deficient mice, hepatotoxity is readily manipulated by administering or withdrawing the drug NTBC which inhibits Hpd. Alternately, Hpd can be blocked with a shRNA. We've previously shown that in Fah-deficient mice, hepatocytes transduced with an Hpd-specific shRNA have a selective advantage when NTBC is withdrawn, leading to clonal expansion of transduced cells.This Hpd-specific shRNA was incorporated into the original albumin-targeting 2A integration vector as an shRNAmir. To prevent off-target expression, the shRNAmir was inserted without a promoter into an intron of the vector's 3’ albumin homology arm. The resulting AAV-8 vector was administered to Fah-deficient neonates (P0, n=8) by facial vein injection at a dose of 4e11 Vg. At 4 weeks of age, plasma hF-IX levels measured 167 +/- 65 ng/ml. The mice were then cycled off NTBC to select for hepatocytes rescued through expression of the Hpd shRNAmir. Plasma hF-IX levels increased exponentially, reaching 46, 000 +/- 5, 000 ng/ml after 11 weeks of NTBC cycling (n=4). Three of the treated mice were cycled off NTBC for just 3 weeks, then maintained on NTBC for an additional 6 weeks. hF-IX levels remained steady at 400 – 1100 ng/ml, suggesting the integrated sequences were not toxic to hepatocytes. Control mice treated with the original albumin integration vector (lacking the HPD shRNAmir) showed no increase in plasma hF-IX levels during NTBC cycling. Administration of the selectable AAV to adult mice also resulted in increased hF-IX during NTBC withdrawal. Current efforts aim to replicate selection in wild-type mice using pharmacological inhibition of Fah.In summary, 2A fusion-based integration vectors promise significant safety advantages over traditional gene targeting methods. We've shown that incorporating selectable genetic elements into these vectors facilitates highly robust transgene expression which can be modulated in vivo. Selectable vectors could allow significantly lower vector doses, thereby enhancing the safety of such therapies even further.

A modular gene targeting system for sequential transgene stacking in plants

A modular, selection-based method was developed for site-specific integration of transgenes into a genomic locus to create multigene stacks. High-frequency gene targeting was obtained using zinc finger nuclease (ZFN)-mediated double-strand break (DSB) formation at a pre-defined target genomic location using a unique intron directly downstream of a promoter driving a selectable marker gene to facilitate homology between target and donor sequences. In this system, only insertion into the target locus leads to a functional selectable marker, and regeneration from random insertions of the promoterless donor construct are reduced on selection media. A new stack of transgenes can potentially be loaded with each successive cycle of gene targeting by exchanging the selectable marker gene using the intron homology. This system was tested in maize using the pat selectable marker gene, whereby up to 30% of the plants regenerated on Bialaphos-containing medium were observed to have the donor construct integrated into the target locus. Unlike previous gene targeting methods that utilize defective or partial genes for selecting targeted events, the present method exchanges fully functional genes with every cycle of targeting, thereby allowing the recycling of selectable marker genes, hypothetically for multiple generations of gene targeting.

A new vector for efficient gene targeting to the pyrG locus in Aspergillus niger.

BackgroundThe possibility for efficient gene targeting for the controlled integration of DNA constructs is an important tool in fungal genetics.FindingsIn this study, we report a new targeting vector based on the pyrG marker in Aspergillus niger. The DNA sequence to be targeted is surrounded by two fragments of the pyrG gene to allow homologous recombination of the recombinant DNA at the pyrG locus. The 5’ end of the targeting cassette contains a non-functional truncated pyrG open reading frame (first 112 bases deleted) and the 3’ untranslated region (3’ UTR). At the 3’ end, the targeting cassette consists of the 3’ flanking region of the pyrG gene. A unique NotI site between the flanks allows the insertion of a gene of interest. The linearized targeting cassette is transformed to the A. niger pyrG mutant strain AB4.1 or a derivative thereof. By using a constitutively expressed luciferase reporter gene (mluc) as an example, it is shown that the targeting system is efficient as 4 out of 6 (67%) AB4.1 transformants and 51 out of 66 (77%) MA169.4 (ku70 −) transformants contained the reporter gene at the pyrG locus. A luciferase (lux) activity assay, performed with independently obtained transformants in which the mluc reporter was integrated at the pyrG locus, showed comparable and reproducible lux activities.ConclusionThe new pyrG targeting vector is an important improvement to the existing method for gene targeting in A. niger. Although the vector is specific for A. niger, the presented design and approach is easily applicable for constructing integration vectors for other fungi.

Current progress of targetron technology: development, improvement and application in metabolic engineering.

Targetrons are mobile group II introns that can recognize their DNA target sites by base-pairing RNA-DNA interactions with the aid of site-specific binding reverse transcriptases. Targetron technology stands out from recently developed gene targeting methods because of the flexibility, feasibility, and efficiency, and is particularly suitable for the genetic engineering of difficult microorganisms, including cellulolytic bacteria that are considered promising candidates for biomass conversion via consolidated bioprocessing. Along with the development of the thermotargetron method for thermophiles, targetron technology becomes increasingly important for the metabolic engineering of industrial microorganisms aiming at biofuel/chemical production. To summarize the current progress of targetron technology and provide new insights on the use of the technology, this paper reviews the retrohoming mechanisms of both mesophilic and thermophilic targetron methods based on various group II introns, investigates the improvement of targetron tools for high target efficiency and specificity, and discusses the current applications in the metabolic engineering for bacterial producers. Although there are still intellectual property and technical restrictions in targetron applications, we propose that targetron technology will contribute to both biochemistry research and the metabolic engineering for industrial productions.

High frequency of homologous gene disruption by single-stranded DNA in the taxol-producing fungus Pestalotiopsis microspora

Gene disruption in Pestalotiopsis microspora is blocked by the formation of extrachromosomal DNAs with telomeric repeats in transformants generated using the protoplast-PEG approach. In order to avoid this condition and to provide molecular tools, a highly efficient gene targeting method, mediated by single-stranded DNA homologous disruption of Agrobacterium tumefaciens-mediated transformation (ATMT) with one-step construction of Agrobacterium-recombination-ready-plasmids (OSCAR) was established for the first time in this fungus. Conditions affecting recombination for OSCAR were optimized. The polyketide synthase gene pks1—an essential gene for melanin biosynthesis—was selected as a target gene because of the clear phenotypic difference between the pks1 mutant and the wild-type strain. Disruption of pks1 by this method resulted in 80 % albino transformants compared with black colonies of the wild-type strain. Southern analysis and PCR amplification verified that a single-copy homologous recombination event had occurred at the pks1 locus. The pattern of secondary metabolites and the production of conidia were affected by the loss of pks1. This study demonstrated that ATMT with single-stranded DNA is an effective method for gene targeting in Pestalotiopsis microspora, which should facilitate genetic modification in this species. This study also indicates that crosstalk exists between the biosynthesis of melanin and other secondary metabolites in this fungus.

Rapid screening of gene function by systemic delivery of morpholino oligonucleotides to live mouse embryos.

Traditional gene targeting methods in mice are complex and time consuming, especially when conditional deletion methods are required. Here, we describe a novel technique for assessing gene function by injection of modified antisense morpholino oligonucleotides (MOs) into the heart of mid-gestation mouse embryos. After allowing MOs to circulate through the embryonic vasculature, target tissues were explanted, cultured and analysed for expression of key markers. We established proof-of-principle by partially phenocopying known gene knockout phenotypes in the fetal gonads (Stra8, Sox9) and pancreas (Sox9). We also generated a novel double knockdown of Gli1 and Gli2, revealing defects in Leydig cell differentiation in the fetal testis. Finally, we gained insight into the roles of Adamts19 and Ctrb1, genes of unknown function in sex determination and gonadal development. These studies reveal the utility of this method as a means of first-pass analysis of gene function during organogenesis before committing to detailed genetic analysis.

Hitting the Target Without Pulling the Trigger

Targeted genomic integration typically requires designer nucleases that augment gene targeting efficiencies by creating a double-strand DNA (dsDNA) break at the target locus. This break provides the “molecular trigger” necessary to boost the efficiency of homologous recombination by several orders of magnitude. Eliminating the nuclease once it has done its job is highly desirable but remains a challenge. In a recent issue of Nature, Barzel et al. described a promising nuclease-free method for gene targeting by homologous recombination with unexpected high efficiency.1 Promoterless adeno-associated virus (AAV) vectors were designed to specifically target the albumin locus, which is highly expressed in the liver. Consequently, targeted genomic integration of a coagulation factor IX (FIX) complementary DNA into the albumin locus directed sustained FIX expression at therapeutic levels and corrected the bleeding diathesis in hemophilic mice. This approach may ultimately pave the way toward a safer and efficacious liver-directed gene therapy that minimizes the risk of insertional oncogenesis and off-target effects. This is particularly relevant for diseases that manifest themselves in infants and require early treatment by gene therapy.

Novel R41Q-PAR1-Modified Mice Enable Proof-of-Concept Studies for in Vivo Mechanisms of Action for Thrombin (IIa) and Activated Protein C (APC)

Introduction: Thrombin (IIa) and activated protein C (APC) are serine proteases involved in coagulation and inflammatory responses that affect many cell types in the body. IIa employs the GPCR, protease activated receptor 1 (PAR1), to promote endothelial barrier disruption, vascular leakage, and inflammation. In contrast, APC requires PAR1 for its opposing actions to stabilize endothelial barriers and to provide anti-inflammatory and anti-apoptotic activities. Studies of murine in vivo injury models using PAR1 knockout mice show that APC requires PAR1 to reduce sepsis-induced mortality and to provide robust neuroprotection following ischemic stroke. Extensive in vitro studies support the hypothesis that IIa’s cleavage at R41 in PAR1 initiates its signaling. Although APC was long thought, paradoxically, to act also via cleavage at R41, we recently proposed that APC’s cleavage at R46 initiates its endothelial barrier-protective and cytoprotective signaling via biased signaling. Since PAR1 knock-out mice cannot provide mechanistic data for testing these hypotheses in vivo, mice carrying the point mutation of R41 to Q in PAR1 were generated to enable mechanistic studies to test whether or not IIa and APC require Arg41 for their PAR1-dependent effects.Methods: Using C57BL/6-derived embryonic stem cells and standard gene targeting methods, we prepared C57BL/6 mice carrying the PAR1 mutation of R41 to Q. IIa-induced and APC-induced signaling, detected as phosphorylation of ERK1/2 or Akt in Brain Microvascular Endothelial Cells (BECs), was quantified using immunoblotting. BECs were obtained from homozygous 41QQ-PAR1 mice and wild type 41RR-littermates. Endothelial barrier disruption of cultured BECs was assayed using Trans-Endothelial Resistance (TER) assays (iCelligence, Acea, San Diego). Mortality of wild type and 41QQ-PAR1 mutant mice that was caused by live E. coli-induced pneumonia and to endotoxin was determined using standard methods. The ability of a cytoprotective-selective murine APC mutant (5A-APC) to reduce mortality of E.coli-challenged wild type and homozygous mutant mice was determined.Results: Upon breeding of R41Q-PAR1 heterozygous mice, the progeny did not fit a Mendelian pattern and yielded only 14% rather than 25% homozygous 41QQ mice. This reduced yield of homozygous mutant mice was similar to the previously reported low yield of homozygous PAR1 knockout mice. Homozygous 41QQ-PAR1 mice showed normal protein expression in BECs for PAR1 and endothelial cell protein C receptor (EPCR) antigens. When BECs from homozygous mutant mice were compared to those from wild type littermates, the IIa-induced vascular disruption in TER assays was greatly reduced by the mutation. Intracellular Ca2+ release, a hallmark of IIa-induced signaling, was greatly impaired (>90%) in BECs from homozygous mutant mice compared to wild type controls. IIa-induced phosphorylation of ERK1/2 in BECs was also significantly reduced by the mutation whereas APC-induced phosphorylation of Akt was not significantly affected. In murine sepsis-induced mortality studies, homozygosity for the R41Q-PAR1 mutation conveyed considerable resistance to death induced by either E. coli pneumonia or endotoxin in female mice but not in male mice. Tests to determine whether 5A-APC rescued male mice from sepsis-induced lethality showed that homozygous 41QQ-PAR1 mice were entirely responsive to 5A-APC therapy because 5A-APC treatment reduced mortality from 50 % to 0 % (see Figure). Wild type control mice also showed a beneficial response with reduced mortality in response to 5A-APC therapy, as previously described.Conclusions: These studies show that mutation of Arg41 to Gln in murine PAR1 diminishes or eliminates signaling induced by IIa but not by APC. Moreover, the ability of cytoprotective-selective 5A-APC to reduce bacteria-induced septic mortality in 41QQ-PAR1 mutant mice provides strong in vivo proof-of-concept data for PAR1 activation caused by non-canonical cleavage by APC. In summary, the 41QQ-PAR1 mutant mouse provides a unique and powerful tool to define in vivo requirements for cleavage sites that enable PAR1 signaling activities induced by IIa, APC or other proteases. [Display omitted] DisclosuresMosnier:The Scripps Research Institute : The Scripps Research Institute Patents & Royalties. Griffin:The Scripps Research Institute: The Scripps Research Institute Patents & Royalties.

Abstract 13545: MicroRNA-33b Knock-in Mice for an Intron of Sterol Regulatory Element-Binding Factor 1 (Srebf1) Exhibit Reduced HDL-C in vivo

Background: MicroRNAs (miRs) are small non-protein-coding RNAs that bind to specific mRNAs and inhibit translation or promote mRNA degradation. Recent reports, including ours, indicated that miR-33 (miR-33a) located within the intron of sterol regulatory element-binding protein (SREBP) 2 controls cholesterol homeostasis and can be a possible therapeutic target for treating atherosclerosis. Primates, but not rodents, express a second miR-33 gene (miR-33b) from an intron of SREBF1. To address miR-33b function in vivo, we developed humanized mice, in which a miR-33b transgene is inserted within a Srebf1 intron. Methods and Results: The human miR-33b sequence was introduced into intron 16 of mouse Srebf1 by conventional gene targeting methods, because miR-33b is located in intron 16 of human SREBF1 and there are high homologies in exons 16 and 17 between human and mouse. We successfully established miR-33b knock-in (KI) mice with C57BL/6 background and this miR-33b KI strategy did not alter Srebf1 intron 16 splicing, which was confirmed by RT-PCR and sequencing. The expression of miR-33b in miR-33b KI hetero mice were almost half of those in miR-33b KI homo mice. An LXR agonist T0901317, which induces Srebf1 expression, enhanced miR-33b expression in primary hepatocytes and the liver of miR-33 KI homo mice. The protein levels of known miR-33a target genes, such as ABCA1, ABCG1, and SREBP-1, were reduced compared with those in wild-type mice. Peritoneal macrophages from the miR-33b KI mice had a reduced cholesterol efflux capacity via apoA-I and HDL-C. Serum HDL-C levels were reduced by almost 35% even in miR-33b KI hetero mice compared with wild-type mice. HPLC elution analysis showed that the decreased HDL levels were mainly composed of very large-, large-, medium sized HDL, which was compatible with the previous results of miR-33a deficient mice. Conclusions: miR-33b KI mice for an intron of Srebf1 showed reduced HDL-C levels. These results indicate that miR-33b can be a potential target for raising HDL-C in humans and may account for lower HDL-C levels in humans than those in mice. These mice will aid in elucidating the roles of miR-33s in different disease models and in screening of the drugs that can alter miR-33a and miR-33b levels and activities.

Genome editing in rice and wheat using the CRISPR/Cas system.

Targeted genome editing nucleases, such as zinc-finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs), are powerful tools for understanding gene function and for developing valuable new traits in plants. The clustered regularly interspersed short palindromic repeats (CRISPR)/Cas system has recently emerged as an alternative nuclease-based method for efficient and versatile genome engineering. In this system, only the 20-nt targeting sequence within the single-guide RNA (sgRNA) needs to be changed to target different genes. The simplicity of the cloning strategy and the few limitations on potential target sites make the CRISPR/Cas system very appealing. Here we describe a stepwise protocol for the selection of target sites, as well as the design, construction, verification and use of sgRNAs for sequence-specific CRISPR/Cas-mediated mutagenesis and gene targeting in rice and wheat. The CRISPR/Cas system provides a straightforward method for rapid gene targeting within 1-2 weeks in protoplasts, and mutated rice plants can be generated within 13-17 weeks.