Limitations of VS38c labeling in the detection of plasma cell myeloma by flow cytometry

Plasma cell myeloma (multiple myeloma [MM]) is a malignant neoplasm originating from the plasma cells. Besides other methods, flow cytometric analysis of the patient's bone marrow aspirate has an important role in the diagnosis and also in the response assessment. Since the cell surface markers, used for identifying abnormal plasma cells, are expressed diversely and the treatment can also alter the phenotype of the plasma cells, there is an increasing demand for new plasma cell markers. VS38c is a monoclonal antibody that recognizes the CLIMP-63 protein in the membrane of the endoplasmic reticulum. CLIMP-63 is known to be expressed at high levels in normal and pathologic plasma cells in the bone marrow, thus VS38c antibody can be used to identify them. Although VS38c staining of plasma cells is reported to be constant and strong even in myeloma, we were wondering whether sample preparation can affect the staining. We have investigated the effect of different permeabilization agents and washing of the cells on the quality of the VS38c staining and found that in many cases the staining is inadequate to identify the plasma cells. We measured the VS38c staining of the bone marrow aspirates of 196 MM patients and observed that almost all cases showed bright staining with VS38c. However, permeabilization with mild detergent resulted in the appearance of a significant VS38c^dim subpopulation, which showed increased sensitivity to mechanical stress (centrifugation). Our results indicate that VS38c^dim MM cells can appear due to the improper permeabilization of the endoplasmic reticulum and this finding raises the possibility of the existence of a plasma cell subpopulation with different membrane properties. The significance of this population is unclear yet, but these cells can be easily missed with VS38c staining and can be lost due to centrifugation-induced lysis during sample preparation.

Intracellular Labeling with Extrinsic Probes: Delivery Strategies and Applications

Extrinsic probes have outstanding properties for intracellular labeling to visualize dynamic processes in and of living cells, both in vitro and in vivo. Since extrinsic probes are in many cases cell-impermeable, different biochemical, and physical approaches have been used to break the cell membrane barrier for direct delivery into the cytoplasm. In this Review, these intracellular delivery strategies are discussed, briefly explaining the mechanisms and how they are used for live-cell labeling applications. Methods that are discussed include three biochemical agents that are used for this purpose-purpose-different nanocarriers, cell penetrating peptides and the pore-foraming bacterial toxin streptolysin O. Most successful intracellular label delivery methods are, however, based on physical principles to permeabilize the membrane and include electroporation, laser-induced photoporation, micro- and nanoinjection, nanoneedles or nanostraws, microfluidics, and nanomachines. The strengths and weaknesses of each strategy are discussed with a systematic comparison provided. Finally, the extrinsic probes that are reported for intracellular labeling so-far are summarized, together with the delivery strategies that are used and their performance. This combined information should provide for a useful guide for choosing the most suitable delivery method for the desired probes.

Fluorescence and Cytotoxicity of Cadmium Sulfide Quantum Dots Stabilized on Clay Nanotubes

Quantum dots (QD) are widely used for cellular labeling due to enhanced brightness, resistance to photobleaching, and multicolor light emissions. CdS and CdxZn₁-xS nanoparticles with sizes of 6⁻8 nm were synthesized via a ligand assisted technique inside and outside of 50 nm diameter halloysite clay nanotubes (QD were immobilized on the tube's surface). The halloysite⁻QD composites were tested by labeling human skin fibroblasts and prostate cancer cells. In human cell cultures, halloysite⁻QD systems were internalized by living cells, and demonstrated intense and stable fluorescence combined with pronounced nanotube light scattering. The best signal stability was observed for QD that were synthesized externally on the amino-grafted halloysite. The best cell viability was observed for CdxZn₁-xS QD immobilized onto the azine-grafted halloysite. The possibility to use QD clay nanotube core-shell nanoarchitectures for the intracellular labeling was demonstrated. A pronounced scattering and fluorescence by halloysite⁻QD systems allows for their promising usage as markers for biomedical applications.

Transport and release of colloidal 3-mercaptopropionic acid-coated CdSe-CdS/ZnS core-multishell quantum dots in human umbilical vein endothelial cells

Colloidal semiconductor quantum dots (QDs) have been extensively researched and developed for biomedical applications, including drug delivery and biosensing assays. Hence, it is pivotal to understand their behavior in terms of intracellular transport and toxicological effects. In this study, we focused on 3-mercaptopropionic acid-coated CdSe-CdS/ZnS core-multishell quantum dots (3MPA-QDs) converted from the as-grown octadecylamine-coated quantum dots (ODA-QDs) and their direct and dynamic interactions with human umbilical vein endothelial cells (HUVECs). Live cell imaging using confocal fluorescence microscopy showed that 3MPA-QDs first attached to and subsequently aggregated on HUVEC plasma membrane ~25 min after QD deposition. The aggregated QDs started being internalized at ~2 h and reached their highest internalization degree at ~24 h. They were released from HUVECs after ~48 h. During the 48 h period, the HUVECs responded normally to external stimulations, grew, proliferated and wound healed without any perceptible apoptosis. Furthermore, 1) 3MPA-QDs were internalized in newly formed LysoTracker-stained early endosomes; 2) adenosine 5′-triphosphate-induced [Ca²⁺]_i modulation caused a transient decrease in the fluorescence of 3MPA-QDs that were attached to the plasma membrane but a transient increase in the internalized 3MPA-QDs; and 3) fluorescence signal modulations of co-stained LysoTracker and QDs induced by the lysosomotropic agent Gly-Phe-β-naphthylamide were spatially co-localized and temporally synchronized. Our findings suggest that 3MPA-QDs converted from ODA-QDs are a potential nontoxic fluorescent probe for future use in clinical applications. Moreover, the photophysical strategy and techniques reported in this work are easily applicable to study of direct interactions between other nanoparticles and live cells; contributing to awareness and implementation of the safe applications of nanoparticles.

A three-camera imaging microscope for high-speed single-molecule tracking and super-resolution imaging in living cells

Our aim is to develop quantitative single-molecule assays to study when and where molecules are interacting inside living cells and where enzymes are active. To this end we present a three-camera imaging microscope for fast tracking of multiple interacting molecules simultaneously, with high spatiotemporal resolution. The system was designed around an ASI RAMM frame using three separate tube lenses and custom multi-band dichroics to allow for enhanced detection efficiency. The frame times of the three Andor iXon Ultra EMCCD cameras are hardware synchronized to the laser excitation pulses of the three excitation lasers, such that the fluorophores are effectively immobilized during frame acquisitions and do not yield detections that are motion-blurred. Stroboscopic illumination allows robust detection from even rapidly moving molecules while minimizing bleaching, and since snapshots can be spaced out with varying time intervals, stroboscopic illumination enables a direct comparison to be made between fast and slow molecules under identical light dosage. We have developed algorithms that accurately track and co-localize multiple interacting biomolecules. The three-color microscope combined with our co-movement algorithms have made it possible for instance to simultaneously image and track how the chromosome environment affects diffusion kinetics or determine how mRNAs diffuse during translation. Such multiplexed single-molecule measurements at a high spatiotemporal resolution inside living cells will provide a major tool for testing models relating molecular architecture and biological dynamics.

Electrophysiological and morphological properties of rat supratrigeminal premotor neurons targeting the trigeminal motor nucleus

The electrophysiological and morphological characteristics of premotor neurons in the supratrigeminal region (SupV) targeting the trigeminal motor nucleus (MoV) were examined in neonatal rat brain stem slice preparations with Ca(2+) imaging, whole cell recordings, and intracellular biocytin labeling. First, we screened SupV neurons that showed a rapid rise in intracellular free Ca(2+) concentration ([Ca(2+)]i) after single-pulse electrical stimulation of the ipsilateral MoV. Subsequent whole cell recordings were generated from the screened SupV neurons, and their antidromic responses to MoV stimulation were confirmed. We divided the antidromically activated premotor neurons into two groups according to their discharge patterns during the steady state in response to 1-s depolarizing current pulses: those firing at a frequency higher (HF neurons, n = 19) or lower (LF neurons, n = 17) than 33 Hz. In addition, HF neurons had a narrower action potential and a larger afterhyperpolarization than LF neurons. Intracellular labeling revealed that the axons of all HF neurons (6/6) and half of the LF neurons (4/9) entered the MoV from its dorsomedial aspect, whereas the axons of the remaining LF neurons (5/9) entered the MoV from its dorsolateral aspect. Furthermore, the dendrites of three HF neurons penetrated into the principal sensory trigeminal nucleus (Vp), whereas the dendrites of all LF neurons were confined within the SupV. These results suggest that the types of SupV premotor neurons targeting the MoV with different firing properties have different dendritic and axonal morphologies, and these SupV neuron classes may play unique roles in diverse oral motor behaviors, such as suckling and mastication.

Integrated microfluidic system with chemiluminescence detection for single cell analysis after intracellular labeling

This work describes the first application of microchip electrophoresis with chemiluminescence detection (MCE-CL) in single cell analysis. Human red blood cells were assayed to determine intracellular content of glutathione (GSH). Intracellular GSH was first labeled by incubating cells with diazo-luminol, and then individual cells were injected, in-line lysed, and MCE separated. CL detection was based on the oxidation reaction of luminol-labeled GSH with NaBrO. The MCE-CL assay had a linear calibration curve over a range from 0.2-90 amol GSH injected with a correlation coefficient of 0.9991 and a detection limit of 50 zmol or 3.6 x 10(-9) M (S/N = 3). The average content of GSH in individual human red blood cells was found 64.9 amol (n = 17). Compared with the MCE methods with laser induced fluorescence detection (LIF) reported so far for single cell analysis, the present MCE-CL assay of GSH is simple and about 100 times more sensitive.

Columnar organization of dendrites and axons of single and synaptically coupled excitatory spiny neurons in layer 4 of the rat barrel cortex

Cortical columns are the functional units of the neocortex that are particularly prominent in the "barrel" field of the somatosensory cortex. Here we describe the morphology of two classes of synaptically coupled excitatory neurons in layer 4 of the barrel cortex, spiny stellate, and star pyramidal cells, respectively. Within a single barrel, their somata tend to be organized in clusters. The dendritic arbors are largely confined to layer 4, except for the distal part of the apical dendrite of star pyramidal neurons that extends into layer 2/3. In contrast, the axon of both types of neurons spans the cortex from layer 1 to layer 6. The most prominent axonal projections are those to layers 4 and 2/3 where they are largely restricted to a single cortical column. In layers 5 and 6, a small fraction of axon collaterals projects also across cortical columns. Consistent with the dense axonal projection to layers 4 and 2/3, the total number and density of boutons per unit axonal length was also highest there. Electron microscopy combined with GABA postimmunogold labeling revealed that most (>90%) of the synaptic contacts were established on dendritic spines and shafts of excitatory neurons in layers 4 and 2/3. The largely columnar organization of dendrites and axons of both cell types, combined with the preferential and dense projections within cortical layers 4 and 2/3, suggests that spiny stellate and star pyramidal neurons of layer 4 serve to amplify thalamic input and relay excitation vertically within a single cortical column.

Synaptic communication among hippocampal interneurons: properties of spontaneous IPSCs in morphologically identified cells

The properties of spontaneous IPSCs (sIPSCs) recorded with whole-cell patch-clamp techniques were investigated in various anatomically identified hippocampal CA1 interneurons and were compared with those recorded in pyramidal cells. Neurons labeled with biocytin or neurobiotin were classified on the basis of their dendritic and axonal arborizations, leading to the identification of previously unknown interneuron types projecting to the dendritic region of pyramidal cells. In most interneurons, the average sIPSCs decayed slower than did those observed in pyramidal cells. The properties of sIPSCs were homogeneous within a given morphologically identified neuron type. Many interneurons had comparable somatic size, location, and dendritic arbor but displayed extremely different axonal projections paralleled by distinct sIPSC properties. Thus, physiological comparisons are only meaningful after the complete morphological identification of the recorded cells. The decay of sIPSCs matched for amplitudes and rise times could vary over 10-fold in a given interneuron, consistent with electrotonic filtering and possibly with different GABAA receptor subunit assemblies present at distinct synapses. Our findings demonstrate an extensive connectivity among hippocampal interneurons through GABAA synapses of various properties that may underlie complex network oscillations at different frequencies.