High-throughput RNA FISH analysis by imaging flow cytometry reveals that pioneer factor Foxa1 reduces transcriptional stochasticity

SUBCELLULAR TRANSCRIPTOMICS & PROTEOMICS: A COMPARATIVE METHODS REVIEW

The internal environment of cells is molecularly crowded, which requires spatial organization via subcellular compartmentalization. These compartments harbor specific conditions for molecules to perform their biological functions, such as coordination of the cell cycle, cell survival, and growth. This compartmentalization is also not static, with molecules trafficking between these subcellular neighborhoods to carry out their functions. For example, some biomolecules are multifunctional, requiring an environment with differing conditions or interacting partners, and others traffic to export such molecules. Aberrant localization of proteins or RNA species has been linked to many pathological conditions, such as neurological, cancer, and pulmonary diseases. Differential expression studies in transcriptomics and proteomics are relatively common, but the majority have overlooked the importance of subcellular information. In addition, subcellular transcriptomics and proteomics data do not always colocate because of the biochemical processes that occur during and after translation, highlighting the complementary nature of these fields. In this review, we discuss and directly compare the current methods in spatial proteomics and transcriptomics, which include sequencing- and imaging-based strategies, to give the reader an overview of the current tools available. We also discuss current limitations of these strategies as well as future developments in the field of spatial -omics.

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Subcellular information of protein and RNA give insights into molecular function.

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This review discusses strategies available to measure subcellular information.

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Hybridization of methods shows promise for exploring the composition of organelles.

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Advances are aiding understanding of the organisation and dynamics of cells.

Virtual-freezing fluorescence imaging flow cytometry

By virtue of the combined merits of flow cytometry and fluorescence microscopy, imaging flow cytometry (IFC) has become an established tool for cell analysis in diverse biomedical fields such as cancer biology, microbiology, immunology, hematology, and stem cell biology. However, the performance and utility of IFC are severely limited by the fundamental trade-off between throughput, sensitivity, and spatial resolution. Here we present an optomechanical imaging method that overcomes the trade-off by virtually freezing the motion of flowing cells on the image sensor to effectively achieve 1000 times longer exposure time for microscopy-grade fluorescence image acquisition. Consequently, it enables high-throughput IFC of single cells at >10,000 cells s⁻¹ without sacrificing sensitivity and spatial resolution. The availability of numerous information-rich fluorescence cell images allows high-dimensional statistical analysis and accurate classification with deep learning, as evidenced by our demonstration of unique applications in hematology and microbiology.

High throughput imaging flow cytometry suffers from trade-offs between throughput, sensitivity and spatial resolution. Here the authors introduce a method to virtually freeze cells in the image acquisition window to enable 1000 times longer signal integration time and improve signal-to-noise ratio.

Self-association and subcellular localization of Puumala hantavirus envelope proteins

Hantavirus assembly and budding are governed by the surface glycoproteins Gn and Gc. In this study, we investigated the glycoproteins of Puumala, the most abundant Hantavirus species in Europe, using fluorescently labeled wild-type constructs and cytoplasmic tail (CT) mutants. We analyzed their intracellular distribution, co-localization and oligomerization, applying comprehensive live, single-cell fluorescence techniques, including confocal microscopy, imaging flow cytometry, anisotropy imaging and Number&Brightness analysis. We demonstrate that Gc is significantly enriched in the Golgi apparatus in absence of other viral components, while Gn is mainly restricted to the endoplasmic reticulum (ER). Importantly, upon co-expression both glycoproteins were found in the Golgi apparatus. Furthermore, we show that an intact CT of Gc is necessary for efficient Golgi localization, while the CT of Gn influences protein stability. Finally, we found that Gn assembles into higher-order homo-oligomers, mainly dimers and tetramers, in the ER while Gc was present as mixture of monomers and dimers within the Golgi apparatus. Our findings suggest that PUUV Gc is the driving factor of the targeting of Gc and Gn to the Golgi region, while Gn possesses a significantly stronger self-association potential.

Toward High-Throughput and Multiplexed Imaging of Genome Organization

Dr. Eric Joyce from the Department of Genetics at the University of Pennsylvania was awarded The President's Innovation award at the annual Society of Biomolecular Imaging and Informatics meeting held in Boston, September 2016. Chromosome interactions are a fundamental aspect of nuclear organization that can activate and silence genes or even direct chromosome rearrangements. However, the molecular mechanisms underlying how chromosomal segments find each other and form stable interactions within cells remain unknown. To address this gap, we have recently developed two technologies that use fluorescent in situ hybridization (FISH) to interrogate chromosome positioning at single-cell resolution. The first is a technology for high-throughput FISH, and the other, called Oligopaints, is a new type of probe that reduces the cost and increases the resolution of FISH. Here, I review our use of these two technologies to uncover and characterize the molecular mechanisms that govern chromosome pairing in Drosophila. I further describe how these methods should benefit a broad spectrum of research fields, including those focusing on chromatin looping, compaction, replication, homologous recombination, and DNA repair.

Fluorescence In situ Hybridization: Cell-Based Genetic Diagnostic and Research Applications

Fluorescence in situ hybridization (FISH) is a macromolecule recognition technology based on the complementary nature of DNA or DNA/RNA double strands. Selected DNA strands incorporated with fluorophore-coupled nucleotides can be used as probes to hybridize onto the complementary sequences in tested cells and tissues and then visualized through a fluorescence microscope or an imaging system. This technology was initially developed as a physical mapping tool to delineate genes within chromosomes. Its high analytical resolution to a single gene level and high sensitivity and specificity enabled an immediate application for genetic diagnosis of constitutional common aneuploidies, microdeletion/microduplication syndromes, and subtelomeric rearrangements. FISH tests using panels of gene-specific probes for somatic recurrent losses, gains, and translocations have been routinely applied for hematologic and solid tumors and are one of the fastest-growing areas in cancer diagnosis. FISH has also been used to detect infectious microbias and parasites like malaria in human blood cells. Recent advances in FISH technology involve various methods for improving probe labeling efficiency and the use of super resolution imaging systems for direct visualization of intra-nuclear chromosomal organization and profiling of RNA transcription in single cells. Cas9-mediated FISH (CASFISH) allowed in situ labeling of repetitive sequences and single-copy sequences without the disruption of nuclear genomic organization in fixed or living cells. Using oligopaint-FISH and super-resolution imaging enabled in situ visualization of chromosome haplotypes from differentially specified single-nucleotide polymorphism loci. Single molecule RNA FISH (smRNA-FISH) using combinatorial labeling or sequential barcoding by multiple round of hybridization were applied to measure mRNA expression of multiple genes within single cells. Research applications of these single molecule single cells DNA and RNA FISH techniques have visualized intra-nuclear genomic structure and sub-cellular transcriptional dynamics of many genes and revealed their functions in various biological processes.

Visualizing the Spatial Relationship of the Genome with the Nuclear Envelope Using Fluorescence In Situ Hybridization

The genome has a special relationship with the nuclear envelope in cells. Much of the genome is anchored at the nuclear periphery, tethered by chromatin binding proteins such nuclear lamins and other integral membrane proteins. Even though there are global assays such as DAM-ID or ChIP to assess what parts of the genome are associated with the nuclear envelope, it is also essential to be able to visualize regions of the genome in order to reveal their individual relationships with nuclear structures in single cells. This is executed by fluorescence in situ hybridization (FISH) in 2-dimensional flattened nuclei (2D-FISH) or 3-dimensionally preserved cells (3D-FISH) in combination with indirect immunofluorescence to reveal structural proteins. This chapter explains the protocols for 2D- and 3D-FISH in combination with indirect immunofluorescence and discusses options for image capture and analysis. Due to the nuclear envelope proteins being part of the non-extractable nucleoskeleton, we also describe how to prepare DNA halos through salt extraction and how they can be used to study genome behavior and association when combined with 2D-FISH.

X-FISH: Analysis of cellular RNA expression patterns using flow cytometry

Fluorescent in situ hybridization (FISH) is a powerful technique for the detection of RNA or DNA within cells and tissues, which provides a unique link between molecular and cell biology. This technique is broadly applicable across a range of biological systems. While FISH has been previously adapted to flow-based platforms, their use remains limited because of procedural challenges and costs associated with commercial kits. Herein we present a protocol that modifies existing techniques to sensitively and specifically detect and examine RNA expression patterns in primary cells and cell lines using flow cytometry (expression-FISH; X-FISH). As relevant examples, we show how this technique can be used to monitor changes in mRNA expression following activation, how it can be combined with antibody staining to study RNA and protein in the same sample, and how it can help distinguish among subsets in a mixed cell population. X-FISH can integrate multiple probes and can be performed in conjunction with other assays, allowing for informative multiparametric analyses and increased statistical robustness. For non-classical comparative animal models this procedure provides a time saving alternative to de novo production of antibody-based markers. Finally, X-FISH provides an economical solution that is applicable to conventional as well as multi-spectral imaging flow cytometry platforms.