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Past Issue in 2024
Volume: 14, Issue: 24
Biophysics
Total Internal Reflection Fluorescence (TIRF) Single-Molecule Assay to Analyze the Motility of Kinesin
The motile parameters of kinesin superfamily proteins are fundamental to intracellular transport. Single-molecule motility assays using total internal reflection fluorescence (TIRF) microscopy are a gold standard technique for measuring the motile parameters of kinesin motors. With this technique, one can evaluate the velocity, run length, and binding frequency of kinesins on microtubules by directly observing their motility. This protocol provides a comprehensive procedure for single molecule assays of kinesins, including the preparation of labeled microtubules, the measurement of kinesin motility via TIRF microscopy, and the quantification of kinesin motor parameters.
Developmental Biology
Egg Microinjection for the Ladybird Beetle Harmonia axyridis
In this paper, we present a detailed protocol for microinjecting DNA, RNA, or protein solutions into fertilized eggs of the multicolored Asian ladybird beetle, Harmonia axyridis, under a stereomicroscope equipped with an injection apparatus. H. axyridis is an emerging model organism for studying various biological fields, showing intraspecific polymorphisms exhibiting highly diverse color patterns on the elytra. Here, we describe how to rear ladybird beetles in a laboratory and obtain fertilized eggs for microinjection experiments. We also provide a constant fluid flow injection method, which enhances the efficiency of microinjection and improves throughput. Our step-by-step protocol is applicable to generating transgenic or genome-edited ladybird beetles, facilitating functional genetics in H. axyridis; the microinjection method should be applicable to other insect eggs.
Live Visualization of Calcified Bones in Zebrafish and Medaka Larvae and Juveniles Using Calcein and Alizarin Red S
Zebrafish and medaka are valuable model vertebrates for genetic studies. The advent of CRISPR-Cas9 technology has greatly enhanced our capability to produce specific gene mutants in zebrafish and medaka. Analyzing the phenotypes of these mutants is essential for elucidating gene function, though such analyses often yield unexpected results. Consequently, providing researchers with accessible and cost-effective phenotype analysis methods is crucial. A prevalent technique for investigating calcified bone development in these species involves using transgenic fish that express fluorescent proteins labeling calcified bones; however, acquiring these fish and isolating appropriate crosses can be time-consuming. We present a comprehensive protocol for visualizing ossified bones in zebrafish and medaka larvae and juveniles using calcein and alizarin red S staining, which is both economical and efficient. This method, applicable to live specimens during the ossification of bones, avoids apparent alterations in skeletal morphology and allows for the use of different fluorescent dyes in conjunction with transgenic labeling, thus enhancing the analysis of developmental processes in calcifying bones, such as vertebrae and fin rays.
Immunology
Isolation of Viral Biofilms From HTLV-1 Chronically Infected T Cells and Integrity Analysis
The human T-lymphotropic virus type-1 (HTLV-1) is an oncogenic retrovirus that predominantly spreads through cell-to-cell contact due to the limited infectivity of cell-free viruses. Among various modes of intercellular transmission, HTLV-1 biofilms emerge as adhesive structures, polarized at the cell surface, which encapsulate virions within a protective matrix. This biofilm is supposed to facilitate simultaneous virion delivery during infection. Yet, the molecular and functional intricacies of viral biofilms remain largely unexplored, despite their pivotal role in understanding retroviral pathogenesis. In this study, we optimized a protocol to isolate HTLV-1 biofilms from chronically infected T cells, facilitating their structural and molecular characterization using proteomic and super-resolution microscopy analyses. This protocol involves cultivating HTLV-1 chronically infected T cells at high density to facilitate the natural detachment of viral biofilms into the supernatant. Then, employing successive centrifugations, the cells are separated from the detached biofilms, and these structures are pelleted at medium speed (10,000× g). This method circumvents the need for mechanical, chemical, or enzymatic biofilm detachment, bypasses the use of ultracentrifugation, and enables us to resuspend the biofilms in the appropriate buffer for subsequent analyses such as western blotting or super-resolution microscopy imaging as presented.
Microbiology
An HPLC-based Assay to Study the Activity of Cyclic Diadenosine Monophosphate (C-di-AMP) Synthase DisA from Mycobacterium smegmatis
Cyclic diadenosine monophosphate (c-di-AMP) is a recently discovered second messenger that modulates several signal transduction pathways in bacterial and host cells. Besides the bacterial system, c-di-AMP signaling is also connected with the host cytoplasmic surveillance pathways (CSP) that induce type-I IFN responses through STING-mediated pathways. Additionally, c-di-AMP demonstrates potent adjuvant properties, particularly when administered alongside the Bacillus Calmette–Guérin (BCG) vaccine through mucosal routes. Because of its pivotal role in bacterial signaling and host immune response, this molecule has garnered significant interest from the pharmaceutical industry. This protocol outlines the quantification of c-di-AMP by an HPLC-based assay to enumerate the activity of c-di-AMP synthase from Mycobacterium smegmatis. The following protocol is designed to be generic, enabling the study of c-di-AMP synthase activity from other bacterial species. However, modifications may be required depending on the specific activity of c-di-AMP synthase from different bacterial sources.
Cryo-SEM Investigation of Chlorella Using Filter Paper as Substrate
Cryo-electron microscopy (cryo-EM) is a powerful technique capable of investigating samples in a hydrated state, compared to conventional high-vacuum electron microscopy that requires samples to be completely dry. During the drying process, numerous features and details may be lost due to damage caused by dehydration. Cryo-EM circumvents these problems by cryo-fixing the samples, thereby retaining the intact and original features of hydrated samples. This protocol describes a step-by-step cryo-scanning electron microscopy (cryo-SEM) experimental procedure with Chlorella sorokiniana as the subject. By employing filter paper as the sample substrate, we propose a simple and reliable method for cryo-fixation and freeze-fracture of Chlorella sorokiniana in water suspension. The advantage of using filter paper as a substrate lies in its ability to support a thin film of sample, enabling a cold knife to make a cut effortlessly and produce a clean freeze-fractured surface for SEM investigation. By following the approach described in this protocol, both the internal structure and surface morphology of Chlorella sorokiniana can be easily resolved with high quality. This protocol is highly versatile and can be applied to samples dispersed in water or solvents, including cyanobacterial cells, algal cells, and any kind of sample that can be adsorbed onto filter paper.
Molecular Biology
An Autocatalytic Platform Combining a Nonlinear Hybridization Chain Reaction and DNAzyme to Detect microRNA
MicroRNAs (miRNAs) are small, non-coding RNAs that play pivotal roles in gene regulation; they are increasingly recognized as vital biomarkers for various diseases, notably cancer. Conventional methods for miRNA detection, such as quantitative PCR and microarray analysis, often entail intricate sample preparation and lack the requisite sensitivity to detect low-abundance miRNAs like miRNA-21. This protocol presents an innovative approach that combines branched hybridization chain reaction (bHCR) with DNAzyme technology for the precise detection of miRNA-21. The bHCR amplifies the target signal through a branched structure, while the DNAzyme boosts detection sensitivity through catalytic cleavage, enabling swift and specific identification of miRNA-21. This dual amplification strategy offers a highly sensitive, specific, and rapid alternative to traditional techniques, making it particularly well-suited for early-stage disease diagnosis.
Assessment of SREBP Activation Using a Microsomal Vesicle Budding Assay
Sterol regulatory element binding proteins (SREBPs) are transcription factors that reside in the endoplasmic reticulum (ER) membrane as inactive precursors. To be active, SREBPs are translocated to the Golgi where the transcriptionally active N-terminus is cleaved and released to the nucleus to regulate gene expression. Nuclear SREBP levels can be determined by immunoblot analysis; however, this method can only determine the steady-state levels of nuclear SREBPs and does not capture the actual status of activation. The vesicle budding assay provides an alternative way to quantify the activation of SREBPs by monitoring the initiation of SREBP translocation from the ER to the Golgi through vesicles. Microsomal membranes isolated from the liver are incubated in a reaction buffer containing the necessary components to facilitate vesicle formation. Microsomal membranes and vesicles are isolated and SREBPs are quantified in each by immunoblot analysis. The amount of SREBPs found in the budded vesicles provides an assessment of the SREBP activation in the liver.
Neuroscience
Microdissection and Single-Cell Suspension of Neocortical Layers From Ferret Brain for Single-Cell Assays
Brain development is highly complex and dynamic. During this process, the different brain structures acquire new components, such as the cerebral cortex, which builds up different germinal and cortical layers during its development. The genetic study of this complex structure has been commonly approached by bulk-sequencing of the entire cortex as a whole. Here, we describe the methodology to study this layered tissue in all its complexity by microdissecting two germinal layers at two developmental time points. This protocol is combined with a step-by-step explanation of tissue dissociation that provides high-quality cells ready to be analyzed by the newly developed single-cell assays, such as scRNA-seq, scATAC-seq, and TrackerSeq. Altogether, this approach increases the resolution of the genetic analyses from the cerebral cortex compared to bulk studies. It also facilitates the study of laboratory animal models that recapitulate human cortical development better than mice, like ferrets.
Plant Science
Immunofluorescence for Detection of TOR Kinase Activity In Situ in Photosynthetic Organisms
The target of rapamycin (TOR) is a central hub kinase that promotes growth and development in all eukaryote cells. TOR induces protein synthesis through the phosphorylation of the S6 kinase (S6K), which, in turn, phosphorylates ribosomal S6 protein (RPS6) increasing this anabolic process. Therefore, S6K and RPS6 phosphorylation are generally used as readouts of TOR activity. Protein phosphorylation levels are measured by a western blot (WB) technique using an antibody against one specific phosphosite in cell extracts. However, at the tissue/cell-specific level, there is a huge gap in plants due to the lack of alternative techniques for the evaluation of TOR activity as there are for other organisms such as mammals. Here, we describe an in vivo protocol to detect S6K phosphorylation in tissues/cells of model photosynthetic organisms such as Arabidopsis thaliana and Chlamydomonas reinhardtii. Our proposed method consists of the immunolocalization of a phosphorylated target of TOR kinase using a fluorescent secondary antibody by confocal microscopy. The protocol involves four main steps: tissue/cell fixation, permeabilization, and incubation with primary and secondary antibodies. It is an easy technique that allows handling different samples at the same time. In addition, different ultrastructural cell markers can also be used, such as for nucleus and cell wall detection, allowing a detailed analysis of cell morphology. To our knowledge, this is the first protocol to detect TOR activity in situ in photosynthetic organisms; we consider that it will pave the research on the TOR kinase, opening new possibilities to better understand its complex signaling.
Stem Cell
CRISPR/Cas9-Based Protocol for Precise Genome Editing in Induced Pluripotent Stem Cells
The advent of clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9-based genome editing has marked a significant advancement in genetic engineering technology. However, the editing of induced pluripotent stem cells (iPSCs) with CRISPR presents notable challenges in ensuring cell survival and achieving high editing efficiency. These challenges become even more complex when considering the specific target site. P53 activation as a result of traditional CRISPR editing can lead to apoptosis, potentially worsening cell health or even resulting in cell death. Mitigating this apoptotic response can enhance cell survival post-CRISPR editing, which will ultimately increase editing efficiency. In our study, we observed that combining p53 inhibition with pro-survival small molecules yields a homologous recombination rate of over 90% when using CRISPR in human iPSCs. This protocol significantly streamlines the editing process and reduces the time and resources necessary for creating isogenic lines.
Systems Biology
Muscle Biopsy Sample Preparation and Proteomics Analysis Based on UHPLC-MS/MS
Proteomics analysis is crucial for understanding the molecular mechanisms underlying muscle adaptations to different types of exercise, such as concentric and eccentric training. Traditional methods like two-dimensional gel electrophoresis and standard mass spectrometry have been used to analyze muscle protein content and modifications. This protocol details the preparation of muscle samples for proteomics analysis using ultra-high-performance liquid chromatography (UHPLC). It includes steps for muscle biopsy collection, protein extraction, digestion, and UHPLC-based analysis. The UHPLC method offers high-resolution separation of complex protein mixtures, providing more detailed and accurate proteomic profiles compared to conventional techniques. This protocol significantly enhances sensitivity, reproducibility, and efficiency, making it ideal for comprehensive muscle proteomics studies.