Two CRISPR/Cas9-mediated methods for targeting complex insertions, deletions, or replacements in mouse

Genetically modified model organisms are valuable tools for probing gene function, dissecting complex signaling networks, studying human disease, and more. CRISPR/Cas9 technology has significantly democratized and reduced the time and cost of generating genetically modified models to the point that small gene edits are now routinely and efficiently generated in as little as two months. However, generation of larger and more sophisticated gene-modifications continues to be inefficient. Alternative ways to provide the replacement DNA sequence, method of Cas9 delivery, and tethering the template sequence to Cas9 or the guide RNA (gRNA) have all been tested in an effort to maximize homology-directed repair for precise modification of the genome. We present two CRISPR/Cas9 methods that have been used to successfully generate large and complex gene-edits in mouse. In the first method, the Cas9 enzyme is used in conjunction with two sgRNAs and a long single-stranded DNA (lssDNA) template prepared by an alternative protocol. The second method utilizes a tethering approach to couple a biotinylated, double-stranded DNA (dsDNA) template to a Cas9-streptavidin fusion protein.

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Alternative method for generating long, single-stranded DNA templates for CRISPR/Cas9 editing.

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Demonstration that using two sgRNAs with Cas9-streptavidin/biotinylated-dsDNA is feasible for large DNA modifications.

Direction Matters: Monovalent Streptavidin/Biotin Complex under Load

Novel site-specific attachment strategies combined with improvements of computational resources enable new insights into the mechanics of the monovalent biotin/streptavidin complex under load and forced us to rethink the diversity of rupture forces reported in the literature. We discovered that the mechanical stability of this complex depends strongly on the geometry in which force is applied. By atomic force microscopy-based single molecule force spectroscopy we found unbinding of biotin to occur beyond 400 pN at force loading rates of 10 nN/s when monovalent streptavidin was tethered at its C-terminus. This value is about twice as high than that for N-terminal attachment. Steered molecular dynamics simulations provided a detailed picture of the mechanics of the unbinding process in the corresponding force loading geometries. Using machine learning techniques, we connected findings from hundreds of simulations to the experimental results, identifying different force propagation pathways. Interestingly, we observed that depending on force loading geometry, partial unfolding of N-terminal region of monovalent streptavidin occurs before biotin is released from the binding pocket.

Hybrid PET/optical imaging of integrin αVβ3 receptor expression using a (64)Cu-labeled streptavidin/biotin-based dimeric RGD peptide

BACKGROUND

Hybrid PET/optical imaging provides quantitative and complementary information for diagnosis of tumors. Herein, we developed a (64)Cu-labeled AlexaFluor 680-streptavidin ((AF)SAv)/biotin-based dimeric cyclic RGD peptide (RGD2) for hybrid PET/optical imaging of integrin αVβ3 expression.

METHODS

(64)Cu-1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid (DOTA)-(AF)SAv/biotin-PEG-RGD2 was prepared by formation of a complex comprising DOTA-(AF)SAv and biotin-PEG-RGD2, followed by radiolabeling with (64)Cu. Receptor binding studies of DOTA-(AF)SAv/biotin-PEG-RGD2 were performed using U87MG cells and (125)I-RGDyK as the radioligand, and cellular uptake studies of (64)Cu-DOTA-(AF)SAv/biotin-PEG-RGD2 were also performed. MicroPET imaging followed by optical imaging of U87MG tumor-bearing mice was acquired after injection of the hybrid probe, and region of interest (ROI) analysis of tumors was performed. Ex vivo PET/optical imaging and biodistribution studies of the major tissues were performed after the in vivo imaging, and immunofluorescence staining of the tumor tissue sections was carried out.

RESULTS

(64)Cu-DOTA-(AF)SAv/biotin-PEG-RGD2 was prepared in 52.1 ± 5.4 % radiochemical yield and with specific activity of 1.0 ± 0.1 GBq/mg. Receptor binding studies showed that DOTA-(AF)SAv/biotin-PEG-RGD2 had higher binding affinity for integrin αVβ3 than RGD2, reflecting a possible polyvalency effect. Moreover, the hybrid probe revealed time-dependent uptake by U87MG cells. In a microPET/optical imaging study, the hybrid probe demonstrated high accumulation in tumors; ROI analysis revealed 2.7 ± 0.2 % ID/g at 1 h and 4.7 ± 0.2 % ID/g at 21 h after injection, and subsequently acquired optical images showed tumors with strong fluorescence intensity. Ex vivo PET/optical images of the major tissues confirmed the in vivo imaging data, and biodistribution studies demonstrated high and specific uptake in tumors (4.8 ± 0.1 % ID/g). Immunofluorescence staining showed the formation of new blood vessels in tumor tissues, suggesting that the tumor uptake was due to specific binding of the hybrid probe to integrin αVβ3 expressed on tumor cells.

CONCLUSIONS

These results indicate that a (64)Cu-DOTA-(AF)SAv/biotin-PEG-RGD2 is able to provide quantitative information on hybrid PET/optical imaging of integrin αVβ3 expression.

[Development of an antigen 'sandwich' enzyme immunoassay for the detection of antibodies against HIV-2 by using a biotinylated synthetic peptide of gp36 protein]

INTRODUCTION

Among the several existing methods for the detection of antibodies to HIV, the 'sandwich' ELISA is currently the most used. This study aims to assess a biotinylated monomeric synthetic peptide of the glycoprotein trans-membrane gp36 from HIV-2, in a sandwich assay, for the detection of antibodies against this HIV-2 protein.

MATERIALS AND METHODS

To perform the assay, plates coated with recombinant protein gp36 at 0.5μg/mL and synthetic peptide gp36(5) at 1μg/mL were used. The concentration of the biotinylated synthetic peptide (gp36(5)-B) used was 0.1μg/mL prepared with a Tris-BSA-NaCl buffer solution and the Streptavidin- Alkaline Phosphatase conjugate diluted 1:30000 prepared with a PBS-Sucrose-BSA solution. Positive serum samples to antibodies against HIV-1 and HIV-2 viruses (88 and 34, respectively) were tested, with 483 negative samples from blood donors and 96 serum samples to assess the analytical specificity. All the samples were tested using the UMELISA HIV 1+2 RECOMBINANT assay, and all positives were confirmed using a DAHIV-BLOT assay.

RESULTS

Thirty four samples with antibodies against HIV-2 were assessed as positive for both coating variants. The highest specificity was obtained with the variant using the synthetic peptide gp36(5) in its coating. The antigen 'sandwich' assay developed by using gp36(5)-B enables the detection of antibodies against gp36 protein of HIV-2.