No abstract

Bulk studies are not suitable to describe and study cell-to-cell variation, which is of high importance in biological processes such as embryogenesis, tissue differentiation, and disease. Previously, capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) was used to measure the properties of organelles isolated from millions of cells. As such, these bulk measurements reported average properties for the organelles of cell populations. Similar measurements for organelles released from single cells would be highly relevant to describe the subcellular variations among cells. Toward this goal, here we introduce an approach to analyze the mitochondria released from single mammalian cells. Osteosarcoma 143B cells are labeled with either the fluorescent mitochondrion-specific 10-N-nonyl acridine orange (NAO) or via expression of the fluorescent protein DsRed2. Subsequently, a single cell is introduced into the CE-LIF capillary where the organelles are released by a combined treatment of digitonin and trypsin. After this treatment, an electric field is applied and the released organelles electromigrate toward the LIF detector. From an electropherogram, the number of detected events per cell, their individual electrophoretic mobilities, and their individual fluorescence intensities are calculated. The results obtained from DsRed2 labeling, which is retained in intact mitochondria, and NAO labeling, which labels all mitochondria, are the basis for discussion of the strengths and limitations of this single-cell approach.

We report the doxorubicin content in individual organelles following their capillary electrophoretic separation and illustrate that chemical accumulation at the subcellular level is highly heterogeneous. In individual mitochondria from cultured human leukemia cells DOX amount is around 50 zmol, 2 orders of magnitude higher than expected from diffusion during drug treatment, and spans 2 orders of magnitude.

No abstract

CE analysis of the acidic organelles of a single cellThe properties of organelles within a cell have been shown to be highly heterogeneous. Until now, it has been unclear just how much of this heterogeneity is endemic to the organelle subpopulations themselves and how much is actually due to stochastic cellular noise. An attractive approach for investigating the origins of heterogeneity among the organelles of a single cell is CE with LIF detection (CE-LIF). As a proof of principle, in this report we optimize and use a single cell CE-LIF method to investigate the properties of endocytic (acidic) organelles. Our results show that the properties of individual acidic organelles containing Alexa Fluor ® 488 Dextran suggest that there are two groups of CCRF-CEM cells: a group with a high dextran content per cell, and a group with a low dextran content per cell. Furthermore, the individual organelle measurements of the single cells allow us to compare in each group the distributions of doxorubicin content per acidic organelle and electrophoretic mobilities of these organelles. Keywords IntroductionHeterogeneity among cells of the same type is known to result partly from intracellular processes, such as pinocytosis [1], the expression of proteins participating in DNA replication [2], and cellular responses to drug treatments [3], and partly from the microenvironment in which the cells reside [4]. Within the cell, heterogeneity at the subcellular level, which refers to variations in the properties of organelles of a given type, has remained practically uncharacterized up to this point. There is a great need to develop and apply single cell approaches capable of measuring the different facets of cellular heterogeneity at the subcellular level. Among the existing techniques for investigating subcellular heterogeneity, chemical imaging has been used to probe the heterogeneity of subcellular properties such as organellar pH, ion concentration, and protein interactions [5,6]. Flow cytometry [7] and CE with LIF detection (CE-LIF) [7,8] have both been used to analyze individual organelles in samples prepared from thousands to millions of cells. With all of these techniques, it has been impossible to track down which organelles originate from the same cell, information that is needed if we are to determine cell-to-cell variations.In order to determine cell-to-cell variations, single cells have been analyzed by CE [9], chromatography [10], MS [11], enzymatic radiolabeling [12], sensitive voltammetric detection [13], and flow cytometry [14]. CE has been used to describe the contents and functions of single cells (e.g., protein expression [15], release of neurotransmitters, and cell secretion [16]). In regard to the subcellular analysis of single cells, CE has been used to sample small subcellular regions, and to measure properties of the whole nucleus of a single cell [17,18]. The ability to detect individual mitochondrial particles by CE-LIF after their release from single cells has been recently described [19]. This report sho...