Microscopic Analysis of Cell Fate Alteration Induced by Cell Fusion

In mammals, differentiated cells generally do not de-differentiate nor undergo cell fate alterations. However, they can be experimentally guided toward a different lineage. Cell fusion involving two different cell types has long been used to study this process, as this method induces cell fate alterations within hours to days in a subpopulation of fused cells, as evidenced by changes in gene-expression profiles. Despite the robustness of this system, its use has been restricted by low fusion rates and difficulty in eliminating unfused populations, thereby compromising resolution. In this study, we address these limitations by isolating fused cells using antibody-conjugated beads. This approach enables the microscopic tracking of fused cells starting as early as 5 hours after fusion. By taking advantage of species-specific FISH probes, we show that a small population of fused cells resulting from the fusion of mouse ES and human B cells, expresses OCT4 from human nuclei at levels comparable to human induced pluripotent stem cells (iPSCs) as early as 25 hours after fusion. We also show that this response can vary depending on the fusion partner. Our study broadens the usage of the cell fusion system for comprehending the mechanisms underlying cell fate alterations. These findings hold promise for diverse fields, including regenerative medicine and cancer.

Optimizing Tissue Preservation for High-Resolution Confocal Imaging of Single-Molecule RNA-FISH

Over the past century, formalin-fixed, paraffin-embedded (FFPE) tissue samples have represented the standard for basic histology and immunostaining. However, FFPE has several limitations and less stringent tissue preservation methods are required for the visualization of nucleic acids at high resolution, particularly those that are expressed at low levels. Here, we describe the FFPE properties that negatively impact RNA integrity, an alternative tissue preservation technique that prevents RNA loss, and the steps necessary to optimize slide preparation for single-molecule RNA fluorescent in situ hybridization (smRNA-FISH) and imaging by confocal microscopy. This strategy retains RNA quality and eliminates formalin-induced artifacts, thereby producing high-resolution, diffraction-limited confocal images of even rare RNA transcripts in tissues. As non-coding RNAs and alternative splicing of gene isoforms continue to emerge as important regulators of human health and disease, a reliable, cost-effective approach is required to examine the expression and localization of RNA targets in patient samples. © 2019 by John Wiley & Sons, Inc. Basic Protocol 1: Preparing an RNase-free workstation Support Protocol 1: Diethyl pyrocarbonate water treatment Support Protocol 2: Removing RNase contamination from glassware Basic Protocol 2: BE70 tissue fixation and processing Basic Protocol 3: Cutting slide sections from paraffin blocks Basic Protocol 4: Specimen pre-treatment Basic Protocol 5: RNA fluorescent in situ hybridization labeling Basic Protocol 6: Slide mounting Basic Protocol 7: Generating deconvolution-capable confocal micrographs.