细胞生物学

Macrophages are known for engulfing and digesting pathogens and dead cells through a specialized form of endocytosis called phagocytosis. Unfortunately, many macrophage cell lines are refractory to most reagents used for transient transfections. Alternative transient approaches, such as electroporation or transduction with lentiviral vectors, typically cause cell death (electroporation) or can be time-consuming to generate numerous lentivirus when using different genes of interest. Therefore, we use the Sleeping Beauty system to generate stably transfected cells. The system uses a “resurrected” transposase gene named Sleeping Beauty found in salmonid fish. Experimentally, the system introduces two plasmids: one carrying the Sleeping Beauty transposase and the other with an integration cassette carrying the gene of interest, a reverse-doxycycline controlled repressor gene, and an antibiotic resistance gene. The construct used in this protocol provides puromycin resistance. Stable integrations are selected by culturing the cells in the presence of puromycin, and further enrichment can be obtained using fluorescence-activated cell sorting (FACS). In this protocol, we use the Sleeping Beauty transposon system to generate RAW264.7 cells with doxycycline-inducible inositol polyphosphate 4-phosphatase B containing a C-terminal CaaX motif (INPP4B-CaaX). INPP4B-CaaX dephosphorylates the D-4 position of phosphatidylinositol 3,4-bisphosphate and inhibits phagocytosis. One benefit is that generating stable cell lines is substantially faster than selecting for random integrations. Without FACS, the method typically gives ~50% of the cells that are transfected; with sorting, this approaches 100%. This makes phagocytosis experiments easier since more cells can be analyzed per experiment, allowing for population-based measurements where a ~10% transient transfection rate is insufficient. Finally, using the doxycycline-promoter allows for low near endogenous expression of proteins or robust overexpression.

Due to overlapping sequences with linear cognates, identifying internal sequences of circular RNA (circRNA) remains a challenge. Recently, we have developed a full-length circRNA sequencing method (circFL-seq) and computational pipeline, to profile ordinary and fusion circRNA at the isoform level. Compared to short-read RNA-seq, rolling circular reverse transcription and nanopore long-read sequencing of circFL-seq make circRNA reads more than tenfold enriched, and show advantages for identification of both short (<100 nt) and long (>2,000 nt) circRNA transcripts. circFL-seq allows identification of differential alternative splicing suggested wide application prospects for functional studies of internal sequences in circRNAs. In addition, the experimental protocol and computational pipeline of circFL-seq shows better sensitivity and precision for identification of back-splicing junctions than current long-read sequencing methods. Together, the accurate identification and quantification of full-length circRNAs makes circFL-seq a potential tool for large-scale screening of functional circRNAs.

In this protocol, we describe our methods to isolate crypts from patients' biopsy samples and to culture human intestinal stem cells as it’s called “organoid.” Beyond that, we describe how to dissociate organoids cells into single cells for single-cell analysis as a further application. This protocol should provide investigators sufficient tools to generate human organoids from biopsy samples and to accomplish a stable in-vitro assay system.

Ex vivo culture assays of biopsy specimens are advantageous for the experimental evaluation of human circadian characteristics. We developed a simple and non-invasive experimental evaluation method for monitoring the expression of circadian clock genes in an ex vivo culture assay using human hair follicles. This method imposes little burden on subjects. This assay is useful for validating correlations between circadian characteristics in hair follicles and intrinsic characteristics observed in physiological and behavioral studies. While they should be further validated, this ex vivo method constitutes a useful tool for estimating in vivo circadian characteristics.

Cell heterogeneity is high in tissues like lung. Research conducted on pure population of cells usually offers more insights than bulk tissues, such as circadian clock work. In this protocol, we provide a detailed work flow on how to do circadian clock study by RNA seq in laser capture micro-dissected mouse lung club cells. The method uses frozen tissues and is highly reproduciable.

The ability to rapidly assemble and prototype cellular circuits is vital for biological research and its applications in biotechnology and medicine. The Mammalian ToolKit (MTK) is a Golden Gate-based cloning toolkit for fast, reproducible and versatile assembly of large DNA vectors and their implementation in mammalian models. The MTK consists of a curated library of characterized, modular parts that can be assembled into transcriptional units and further weaved into complex circuits. These circuits are easily repurposed and introduced in mammalian cells by different methods.

Cancer cell lines serve as invaluable model systems for cancer biology research and help in evaluating the efficacy of new therapeutic agents. However, cell line contamination and misidentification have become one of the most pressing problems affecting biomedical research. Available methods of cell line authentication suffer from limited access, time-consuming and often costly for many researchers, hence a new and cost-effective approach for cell line authentication is needed. In this regard, we developed a new method called CeL-ID for cell line authentication using genomic variants as a byproduct derived from RNA-seq data. CeL-ID was trained and tested on publicly available more than 900 RNA-seq dataset derived from the Cancer Cell Line Encyclopedia (CCLE) project; including most frequently used adult and pediatric cancer cell lines. We generated cell line specific variant profiles from RNA-seq data using our in-house pipeline followed by pair-wise variant profile comparison between cell lines using allele frequencies and depth of coverage values of the entire variant set. Comparative analysis of variant profiles revealed that they differ significantly from cell line to cell line whereas identical, synonymous and derivative cell lines share high variant identity and their allelic fractions are highly correlated, which is the basis of this cell line authentication protocol. Additionally, CeL-ID also includes a method to estimate the possible cross-contamination using a linear mixture model with any possible CCLE cells in case no perfect match was detected.

This protocol details a method to analyze two tissue samples at the transcriptomic level using microarray analysis, ingenuity pathway analysis (IPA) and gene set enrichment analysis (GSEA). Methods such as these provide insight into the mechanisms underlying biological differences across two samples and thus can be applied to interrogate a variety of processes across different tissue samples, conditions, and the like. The full method detailed below can be applied to determine the effects of muscle-specific Notch1 activation in the mdx mouse model and to analyze previously published microarray data of human liposarcoma cell lines.

RNAi screening technology has revealed unknown determinants of various biological signaling pathways in biomedical studies. This protocol provided detailed information about how to use RNAi screening to identify proliferation determinants in breast tumor cells. siRNA-based libraries targeting against Estrogen receptor (ER)-network, including 631 genes
relevant to estrogen signaling, was constructed for screening in breast cancer cells. Briefly, reverse transfection of siRNA induced transient gene knockdown in MCF7 cells. First, the transfection reagent for MCF7 cells was selected. Next, the Z’-score assay was used to monitor if screening conditions yielded efficiently. Then, the ER-network siRNA library screening was preceded by automatic machines under optimized experimental conditions.

A synthetic lethal interaction is a type of genetic interaction where the disruption of either of two genes individually has little effect but their combined disruption is lethal. Knowledge of synthetic lethal interactions can allow for elucidation of network structure and identification of candidate drug targets for human diseases such as cancer. In Drosophila, combinatorial gene disruption has been achieved previously by combining multiple RNAi reagents. Here we describe a protocol for high-throughput combinatorial gene disruption by combining CRISPR and RNAi. This approach previously resulted in the identification of highly reproducible and conserved synthetic lethal interactions (Housden et al., 2015).