To enable simple and effective high titer recombinant lentivirus production, we examined key parameters for the generation of lentivirus including: transfection optimization, media change, incubation time and DNA vector selection. These results illustrate the importance of optimizing transfection processes for high titer recombinant lentivirus production. Read More
Biological evaluation of hair growth/differentiation activity in vitro has been a formidable challenge, primarily due to the lack of relevant model cell systems. To solve this problem, we generated a stable model cell line in which successive differentiation via epidermal progenitors to hair components is easily inducible and traceable. Mouse induced pluripotent stem (iPS) cell-derived cells were selected to stably express a tetracycline (Tet)-inducible bone morphogenic protein-4 (BMP4) expression cassette and a luciferase reporter driven by a hair-specific keratin 31 gene (krt31) promoter (Tet-BMP4-KRT31-Luc iPS). Read More
Previously, we developed a one-step sequence- and ligation-independent cloning (SLIC) method that is simple, fast, and cost-effective. However, although one-step SLIC generally works well, its cloning efficiency is occasionally poor, potentially due to formation of stable secondary structures within the single-stranded DNA (ssDNA) region generated by T4 DNA polymerase during the 2.5 min treatment at room temperature. Read More
Division of Product Quality Research, Office of Testing and Research, Office of Pharmaceutical Quality, Center for Drug Evaluation and Research (CDER), Food and Drug Administration (FDA), Silver Spring, MD.
Phosphorylation is an important post-translational modification (PTM) of proteins and a critical quality attribute for protein therapeutics, especially if it is required for protein function or sub-cellular targeting. Most current methods to quantify phosphorylation are time-consuming, indirect, or require specific instrumentation and technical skills. Here, we report the adaptation of a phosphate-specific binding dye and common laboratory instruments for quantification of relative amounts of phosphorylated glycans as well as phosphorylation of amino acid residues on the backbones of proteins. Read More
Gene therapy is a fast-developing field of molecular medicine. New, effective, and cancer-specific promoters are in high demand by researchers seeking to treat cancer through expression of therapeutic genes. Here, we created a combinatorial library of tumor-specific chimeric promoter modules for identifying new promoters with desired functions. Read More
Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden.
Address correspondence to Sergey Belikov or Lars Wieslander, Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, SE-106 91 Stockholm, Sweden. E-mail: sergey.belikov@su. Read More
Nanomaterials (NMs) of various types, including carbon nanotubes (CNTs), can interfere with standard quantitative real-time PCR (qRT-PCR) assays, resulting in inaccurate gene expression measurements; however, the precise step in the qRT-PCR pipeline where this interference occurs has not been well described. Here, we investigated where in the process surface-oxidized multi-walled CNTs (oxMWNTs) inhibited qRT-PCR measurement of the expression of the housekeeping gene GAPDH and explored several strategies to minimize such inhibition. We determined that the interference occurred during the reverse transcription (RT) step and found that doubling reaction reagents or adding BSA successfully mitigated the inhibition. Read More
Biotechniques 2017 Aug 1;63(2):77-80. Epub 2017 Aug 1.
M.M. Shemyakin and Yu.A. Ovchinnikov Institute of Bioorganic Chemistry, Moscow, Russian Federation.
In nonpolar solvents, hydrophobic organic fluorophores often show bright fluorescence, whereas in polar media, they usually suffer from aggregation-caused quenching (ACQ). Here, we harnessed this solvatochromic behavior of a 1,3,5,7-tetramethyl-BODIPY derivative for cell staining and applied it to live-cell imaging and flow cytometry. As opposed to commercially available dyes, this BODIPY derivative showed excellent contrast immediately after staining and did not require any wash-off. Read More
Viral vector-mediated foreign gene expression in cultured cells has been extensively used in stem cell studies to explore gene function. However, it is difficult to obtain high-quality stem cells and primary cells after viral vector infection. Here, we describe a new protocol for high-efficiency retroviral infection of primary muscle stem cell (satellite cell) cultures. Read More
Biotechniques 2017 Aug 1;63(2):65-71. Epub 2017 Aug 1.
Institute for the Application of Nuclear Energy, INEP, University of Belgrade, Belgrade, Serbia.
Despite numerous studies, isolating pure preparations of extracellular vesicles (EVs) has proven challenging. Here, we compared ion-exchange chromatography (IEC) to the widely used sucrose density gradient (SDG) centrifugation method for the purification of EVs. EVs in bulk were isolated from pooled normal human amniotic fluid (AF) by differential centrifugation followed by IEC or sucrose density gradient separation. Read More
MicroRNAs (miRNAs) are ~22-nucleotide-long small non-coding RNAs that regulate the expression of protein-coding genes by base pairing to partially complementary target sites, preferentially located in the 3´ untranslated region (UTR) of target mRNAs. The expression and function of miRNAs have been extensively studied in human disease, as well as the possibility of using these molecules as biomarkers for prognostication and treatment guidance. To identify and validate miRNAs as biomarkers, their expression must be screened in large collections of patient samples. Read More
Commercially available lipid-based transfection reagents are widely used to deliver DNA to cells. However, these lipid-based transfection reagents show poor gene transfer efficiency in primary cells. Here, we demonstrate a simple method to improve gene transfer efficiency in primary fibroblasts and hepatoblasts using a combination of lipid-based transfection reagents. Read More
Counting nuclei released from intact cells is a convenient and reliable approach to assess cell density during microcarrier-based culture of adherent cells. However, commonly used methods for counting nuclei, such as crystal violet staining and quantification with a hemocytometer/automated imaging system or a Coulter counter, are imprecise, laborious and, limited in throughput. Here, we describe the use of high-affinity pro-fluorescent nucleic acid stains and volumetric flow cytometry for automated counting of nuclei released from cells attached to microcarriers with improved precision and high sample throughput. Read More
RNA-protein interactions play a major role in gene regulation. Although many techniques to analyze RNA-protein interactions have been developed, noteworthy challenges such as determining the RNA sequences that bind RNA-binding proteins (RBPs) remain unsolved. Here, we describe a novel technique using a 4-thio-uridine-incorporated RNA pool to identify the RBP-binding consensus sequences for RBPs produced by in vitro transcription and translation. Read More
Multiple displacement amplification (MDA) is widely used in whole-genome/transcriptome amplification. However, template-independent amplification (TIA) in MDA is a commonly observed phenomenon, particularly when using high concentrations of random hexamer primers and extended incubation times. Here, we demonstrate that the use of random pentamer primers with 5´ ends blocked by a C18 spacer results in MDA solely in a template-dependent manner, a technique we have named tdMDA. Read More
Current DNA assembly methods are prone to sequence errors, requiring rigorous quality control (QC) to identify incorrect assemblies or synthesized constructs. Such errors can lead to misinterpretation of phenotypes. Because of this intrinsic problem, routine QC analysis is generally performed on three or more clones using a combination of restriction endonuclease assays, colony PCR, and Sanger sequencing. Read More
A major bottleneck for metagenomic sequencing is rapid and efficient DNA extraction. Here, we compare the extraction efficiencies of three magnetic bead-based platforms (KingFisher, epMotion, and Tecan) to a standardized column-based extraction platform across a variety of sample types, including feces, oral, skin, soil, and water. Replicate sample plates were extracted and prepared for 16S rRNA gene amplicon sequencing in parallel to assess extraction bias and DNA quality. Read More
Ancient DNA (aDNA) research involves invasive and destructive sampling procedures that are often incompatible with anthropological, anatomical, and bioarcheological analyses requiring intact skeletal remains. The osseous labyrinth inside the petrous bone has been shown to yield higher amounts of endogenous DNA than any other skeletal element; however, accessing this labyrinth in cases of a complete or reconstructed skull involves causing major structural damage to the cranial vault or base. Here, we describe a novel cranial base drilling method (CBDM) for accessing the osseous labyrinth from the cranial base that prevents damaging the surrounding cranial features, making it highly complementary to morphological analyses. Read More
Biotechniques 2017 Jun 1;62(6):275-282. Epub 2017 Jun 1.
University of Idaho, Department of Chemistry, Moscow, ID.
Single-stranded DNA (ssDNA) oligonucleotides are useful as aptamers, hybridization probes and for emerging applications in DNA nanotechnology. Current methods to purify ssDNA require both a strand-separation step and a separate size-separation step but may still leave double-stranded DNA (dsDNA) impurities in the sample. Here, we use commercially available acrydite DNA primers to immobilize one strand of a PCR product within a polyacrylamide matrix. Read More
The most common gene editing methods, such as CRISPR, involve random repair of an induced double-stranded DNA break through the non-homologous end joining (NHEJ) repair pathway, resulting in small insertions/deletions. In diploid cells, these mutations can take on one of three zygosities: monoallelic, diallelic heterozygous, or diallelic homozygous. While many advances have been made in CRISPR delivery systems and gene editing efficiency, little work has been done to streamline detection of gene editing events. Read More
Optical mapping (OM) has been used in microbiology for the past 20 years, initially as a technique to facilitate DNA sequence-based studies; however, with decreases in DNA sequencing costs and increases in sequence output from automated sequencing platforms, OM has grown into an important auxiliary tool for genome assembly and comparison. Currently, there are a number of new and exciting applications for OM in the field of microbiology, including investigation of disease outbreaks, identification of specific genes of clinical and/or epidemiological relevance, and the possibility of single-cell analysis when combined with cell-sorting approaches. In addition, designing lab-on-a-chip systems based on OM is now feasible and will allow the integrated and automated microbiological analysis of biological fluids. Read More
Biotechniques 2017 Jun 1;62(6):252-253. Epub 2017 Jun 1.
Synthetic biologists have engineered a semisynthetic organism that can store increased genetic information using an alphabet consisting of six letters that form three base pairs. Janelle Weaver learns how they did it. Read More
The advent of genome editing strategies has expanded the range of animal models available for gene manipulation and renewed research interest in the rat. Gender is a key variable for in vivo gene function analyses. Here, we present a simple PCR-based method to determine genetic sex in the rat. Read More
The critical shortage of donor organs has spurred investigation of alternative approaches to either generate replacement organs or implant exogenous cells for treatment of end-stage organ failure. Non-thermal irreversible electroporation (NTIRE), which uses brief high electric field pulses to induce irreversible permeabilization of cell membranes, has emerged as a technique for tumor ablation. Here, we introduce a new application for NTIRE that employs in situ cell ablation to create a niche within a solid organ for engraftment of exogenous cells in vivo. Read More
Here, we describe the properties of a prototype microcentrifuge tube made from the plastic cyclic olefin polymer (COP). This material has been used in the manufacture of primary containers including syringes and vials for the storage, shipment, and delivery of biotherapeutics, vaccines, and cell therapy products. Its low level of extractable substances and metals along with its glass-like clarity make COP an attractive material for the fabrication of microcentrifuge tubes and other consumable laboratory plasticware where contamination is an important consideration, such as in the storage and analysis of labile proteins, nucleic acids, and metabolites. Read More
Embryonic stem cells (ESCs) can be established as permanent cell lines, and their potential to differentiate into adult tissues has led to widespread use for studying the mechanisms and dynamics of stem cell differentiation and exploring strategies for tissue repair. Imaging live ESCs during development is now feasible due to advances in optical imaging and engineering of genetically encoded fluorescent reporters; however, a major limitation is the low spatio-temporal resolution of long-term 3-D imaging required for generational and neighboring reconstructions. Here, we present the ESC-Track (ESC-T) workflow, which includes an automated cell and nuclear segmentation and tracking tool for 4-D (3-D + time) confocal image data sets as well as a manual editing tool for visual inspection and error correction. Read More
Protein-protein interactions critically determine the function of a protein within the cell. Several methods have been developed for the analysis of protein interactions, including two-hybrid assays in yeast and mammals. Mammalian two-hybrid systems provide the ideal physiological environment to study the interactions of mammalian proteins; however, these approaches are limited in sensitivity and their ability to quantify interaction strength. Read More
Recombinant vaccinia viruses (rVACVs) are promising antigen-delivery systems for vaccine development that are also useful as research tools. Two common methods for selection during construction of rVACV clones are (i) co-insertion of drug resistance or reporter protein genes, which requires the use of additional selection drugs or detection methods, and (ii) dominant host-range selection. The latter uses VACV variants rendered replication-incompetent in host cell lines by the deletion of host-range genes. Read More
Two different techniques for genomic DNA fragmentation before microsatellite-enriched library construction-restriction enzyme (NlaIII and MseI) digestion and sonication-were compared to examine their effects on simple sequence repeat (SSR) detection using high-throughput sequencing. Tens of thousands of SSR regions from 5 species of the plant family Myrtaceae were detected when the output of individual samples was >1 million paired-end reads. Comparison of the two DNA fragmentation techniques showed that restriction enzyme digestion was superior to sonication for identification of heterozygous genotypes, whereas sonication was superior for detection of various SSR flanking regions with both species-specific and common characteristics. Read More
Recent advances in biological imaging techniques and the enormous amount of data they generate call for the development of computational tools for efficient and reliable high-throughput analysis. Several software applications with this functionality are available, and one of the most commonly used is ImageJ. Here, we present two independent macros (WH_NJ and SA_NJ) for automating and facilitating the analysis of images acquired from two in vitro assays frequently used in cancer studies and drug screening: the wound-healing and soft-agar assays. Read More
Cell lines expressing foreign genes have been widely used to produce a variety of recombinant proteins. However, generating recombinant protein-expressing cell lines is usually a lengthy process and the resulting protein expression levels are often inconsistent. Here, we describe an efficient method for making stable cell lines expressing any recombinant protein of interest in a controllable and quantifiable manner. Read More
Here, we present a DNA restriction enzyme-based, fluorescent cytosine extension assay (CEA) to improve normalization and technical variation among sample-to-sample measurements. The assay includes end-labeling of parallel methylation-sensitive and methylation-insensitive DNA restriction enzyme digests along with co-purification and subsequent co-measurement of incorporated fluorescence. This non-radioactive, two-color fluorescent CEA (TCF-CEA) was shown to be a relatively rapid and accurate, with 3-fold greater precision than the one-color CEA. Read More
Peptide-major histocompatibility complex (pMHC) multimers enable the detection, characterization, and isolation of antigen-specific T-cell subsets at the single-cell level via flow cytometry and fluorescence microscopy. These labeling reagents exploit a multivalent scaffold to increase the avidity of individually weak T-cell receptor (TCR)-pMHC interactions. Dextramers are an improvement over the original streptavidin-based tetramer technology because they are more multivalent, improving sensitivity for rare, low-avidity T cells, including self/tumor-reactive clones. Read More
Fluorescent immunolabeling and imaging in free-floating thick (50-60 μm) tissue sections is relatively simple in practice and enables design-based non-biased stereology, or 3-D reconstruction and analysis. This method is widely used for 3-D in situ quantitative biology in many areas of biological research. However, the labeling quality and efficiency of standard protocols for fluorescent immunolabeling of these tissue sections are not always satisfactory. Read More
Tissue engineering approaches using growth factors and various materials for repairing chronic perforations of the tympanic membrane are being developed, but there are surprisingly few relevant tissue culture models available to test new treatments. Here, we present a simple three-dimensional model system based on micro-dissecting the rat tympanic membrane umbo and grafting it into the membrane of a cell culture well insert. Cell outgrowth from the graft produced sufficient cells to populate a membrane of similar surface area to the human tympanic membrane within 2 weeks. Read More
Synthetic biologists rely on semi-synthetic recombinant plasmids, but DNA synthesis is constrained by practical limits on length, accuracy, and sequence composition. Cloned DNA parts can be assembled into longer constructs via subcloning, but conventional methods are labor-intensive. One-pot recombination reactions are more convenient but harder to troubleshoot, and those that depend on PCR to create fragments with compatible ends necessitate re-sequencing. Read More