Cell Biology

The formation of spheroids with mesenchymal stem/stromal cells (MSCs), mesenchymal bodies (MBs), is usually performed using bioreactors or conventional well plates. While these methods promote the formation of a large number of spheroids, they provide limited control over their structure or over the regulation of their environment. It has therefore been hard to elucidate the mechanisms orchestrating the structural organization and the induction of the trophic functions of MBs until now. We have recently demonstrated an integrated droplet-based microfluidic platform for the high-density formation and culture of MBs, as well as for the quantitative characterization of the structural and functional organization of cells within them. The protocol starts with a suspension of a few hundred MSCs encapsulated within microfluidic droplets held in capillary traps. After droplet immobilization, MSCs start clustering and form densely packed spherical aggregates that display a tight size distribution. Quantitative imaging is used to provide a robust demonstration that human MSCs self-organize in a hierarchical manner, by taking advantage of the good fit between the microfluidic chip and conventional microscopy techniques. Moreover, the structural organization within the MBs is found to correlate with the induction of osteo-endocrine functions (i.e., COX-2 and VEGF-A expression). Therefore, the present platform provides a unique method to link the structural organization in MBs to their functional properties.

Graphic abstract:

Droplet microfluidic platform for integrated formation, culture, and characterization of mesenchymal bodies (MBs). The device is equipped with a droplet production area (flow focusing) and a culture chamber that enables the culture of 270 MBs in parallel. A layer-by-layer analysis revealed a hierarchical developmental organization within MBs.

To study the inhomogeneity within a cell population including exosomes properties such as exosome secretion rate of cells and surface markers carried by exosomes, we need to quantify and characterize those exosomes secreted by each individual cell. Here we develop a method to collect and analyze exosomes secreted by an array of single cells using antibody-modified glass slides that are position-registered to each single cell. After each collection, antibody-conjugated quantum dots are used to label exosomes to allow counting and analysis of exosome surface proteins. Detailed studies of exosome properties related to cell behaviors such as responses to drugs and stress at single cell resolution can be found in the publication (Chiu et al., 2016).

This protocol describes the extraction, fractionation, and recovery of cytoplasmic nucleic acids (e.g., cytoplasmic RNA) versus nucleic acids in the cell nucleus (including genomic DNA, gDNA) from single cells with a microfluidic system. The method enables independent, sequence-specific analyses of these critical markers (Kuriyama et al., 2015). The system uses a microfluidic chip with a simple geometry and four end-channel electrodes, and completes the entire process in less than 5 min, including lysis, purification, fractionation, and delivery to two output reservoirs: One for the nucleus (including gDNA and nuclear RNA) and one for cytoplasmic RNA. Each reservoir then contains high quality and purity aliquots with no measurable cross-contamination of cytoplasmic RNA versus nucleic acids in nucleus. As described here, our protocol focuses on the analysis of cytoplasmic RNA versus gDNA from the nucleus. We have tested this protocol with mouse and human cells but not with walled cells such as plant cells.

This protocol describes how to use Fluidigm Biomark^TM 96.96 dynamic arrays for high-throughput expression profiling from single mouse stem cells, assaying up to 96 independent samples with up to 96 quantitative PCR (qPCR) probes (equivalent to 9,216 reactions) in a single experiment. This Dynamic Array contains a network of microfluidic channels, chambers and valves that automatically assemble all these individual PCR reactions. Single-cell profiling can provide definitive evidence of stem cell heterogeneity. Modifications are most likely needed if users intend to use Biomark^TM 48.48 Dynamic array or experimenter-designed primers in conjunction with DNA-binding dyes such as EvaGreen (Biotium 31000).