Enrichment of slow-growing marine microorganisms from mixed cultures using gel microdrop (GMD) growth assay and fluorescence-activated cell sorting

Encapsulation of cells in agarose gel microdrops (GMDs) combined with fluorescence-activated cell sorting (FACS) has been used previously to analyze and recover specific mammalian, bacterial, and yeast cell populations. Recently, we have developed a method to enrich mixed bacterial populations for slow-growing microorganisms using the GMD Growth Assay combined with fluorochrome staining and flow cytometry. Here, we demonstrate the feasibility of using this experimental approach to detect clonogenic growth of individual bacteria within GMDs in less than 3 h and to separate subpopulations based on differential growth rates. We show that after sorting, organisms remain viable and can be propagated in culture for further analysis.     

Developmental age-related cell sorting inDictyostelium discoideum

Summary The sorting behavior of mixtures ofD. discoideum cells which had been developed for different lengths of time was examined. Cells developed for 4 and 8 h were mixed together and allowed to form slugs. Within the slugs, 8 h cells sorted to the anterior prestalk region while 4 h cells sorted to the posterior prespore region. These results indicate that the more developed a cell is, the more likely it is to become part of the prestalk zone in the slug. They are also consistent with the differential adhesion and chemotaxis hypotheses as a mechanism for cell sorting since cells become more adhesive and chemotactically responsive as development proceeds.     

Messenger RNA quantification after fluorescence activated cell sorting using intracellular antigens

Recent studies using stem cells or cancer stem cells have revealed the importance of detecting minor populations of cells in blood or tissue and analyzing their biological characteristics. The only possible method for carrying out such procedures is fluorescence activated cell sorting (FACS). However, FACS has the following limitations. First, cells without an appropriate cell surface marker cannot be sorted. Second, the cells have to be kept alive during the sorting process in order to analyze their biological characteristics. If an intracellular antigen that was specific to a particular cell type could be stained with a florescent dye and then the cells can be sorted without causing RNA degradation, a more simple and universal method for sorting and analyzing cells with a specific gene expression pattern could be established since the biological characteristics of the sorted cells could then be determined by analyzing their gene expression profile. In this study, we established a basic protocol for messenger RNA quantification after FACS (FACS-mQ) targeting intracellular antigens. This method can be used for the detection and analysis of stem cells or cancer stem cells in various tissues.     

Enhanced lipid production in Nannochloropsis sp. using fluorescence‐activated cell sorting

To advance the utilization of microalgae as a viable feedstock for biodiesel production, the intracellular lipid content of three strains of the marine microalgae Nannochloropsis sp. was enhanced using flow cytometry (FC) coupled with cell sorting. Total lipid content was doubled to 55% (biomass dry weight) in the sorted, daughter cells of Nannochloropsis (strain 47) after consecutive three rounds of cell sorting, and this trait was maintained for approximately 100 subsequent cell generations. In addition, daughter cells had a fatty acid profile similar to that of the parent, wild‐type strain. The study demonstrates that FC coupled with cell sorting is a powerful tool for the enhancement of intracellular lipid content in microalgae exploited for biodiesel feedstock.     

Cell sorting in cancer research—Diminishing degree of cell heterogeneity

Increasing evidence of intratumor heterogeneity and its augmentation due to selective pressure of microenvironment and recent achievements in cancer therapeutics lead to the need to investigate and track the tumor subclonal structure. Cell sorting of heterogeneous subpopulations of tumor and tumor-associated cells has been a long established strategy in cancer research. Advancement in lasers, computer technology and optics has led to a new generation of flow cytometers and cell sorters capable of high-speed processing of single cell suspensions. Over the last several years cell sorting was used in combination with molecular biological methods, imaging and proteomics to characterize primary and metastatic cancer cell populations, minimal residual disease and single tumor cells. It was the principal method for identification and characterization of cancer stem cells. Analysis of single cancer cells may improve early detection of tumors, monitoring of circulating tumor cells, evaluation of intratumor heterogeneity and chemotherapeutic treatments. The aim of this review is to provide an overview of major cell sorting applications and approaches with new prospective developments such as microfluidics and microchip technologies.     

Magnetic activated cell sorting allows isolation of spermatogonia from adult primate testes and reveals distinct GFRa1‐positive subpopulations in men

Background Isolation of spermatogonial stem cells (SSCs) could enable in vitro approaches for exploration of spermatogonial physiology and therapeutic approaches for fertility preservation. SSC isolation from adult testes is difficult due to low cell numbers and lacking cell surface markers. Glial cell‐derived neurotrophic factor family receptor alpha‐1 (GFRα1) plays a crucial role for the maintenance of SSCs in rodents and is expressed in monkey spermatogonia. Methods Magnetic activated cell sorting was employed for the enrichment of GFRα1+ spermatogonia from adult primate testes. Results Magnetic activated cell sorting of monkey cells enriched GFRα1+ cells threefold. 11.4% of GFRα1+ cells were recovered. 42.9% of GFRα1+ cells were recovered in sorted fractions of human testicular cells, representing a fivefold enrichment. Interestingly, a high degree of morphological heterogeneity among the GFRα1+ cells from human testes was observed. Conclusions Magnetic activated cell sorting using anti‐GFRα1 antibodies provides an enrichment strategy for spermatogonia from monkey and human testes.     

Recovery of a bacterial sub-population from sewage using immunofluorescent flow cytometry and cell sorting

Abstract The effectiveness of immunofluorescence flow cytometry and cell sorting to detect, quantify and separate indigenous bacterial populations present in low concentrations in sewage outflow was investigated. Preparatory experiments for targeted recovery revealed indigenous, immunoglobulin-G-binding particles present at low levels in sewage outflow samples taken from Coniston Water. Fluorescence-activated cell sorting of this population was employed to enrich for these particles, which were confirmed as bacterial cells. This cell population comprised approximately 23% of the total plate count on MacConkey agar before cell sorting, rising to approximately 95% after sorting. These results corresponded to cell densities of less than 5% of the total plate count on R2A agar. Taxonomic tests suggested the bacterium to be Ochrobactrum anthropi .     

A dual-fluorescence reporter system for high-throughput clone characterization and selection by cell sorting

Molecular biology critically depends upon the isolation of desired DNA sequences. Flow cytometry, with its capacity to interrogate and sort more than 50000 cells/s, shows great potential to expedite clone characterization and isolation. Intrinsic heterogeneity of protein expression levels in cells limits the utility of single fluorescent reporters for cell-sorting. Here, we report a novel dual-fluorescence strategy that overcomes the inherent limitations of single reporter systems by controlling for expression variability. We demonstrate a dual-reporter system using the green fluorescent protein (GFP) gene fused to the Discosoma red fluorescent protein (DsRed) gene. The system reports the successful insertion of foreign DNA with the loss of DsRed fluorescence and the maintenance of GFP fluorescence. Single cells containing inserts are readily recognized by their altered ratios of green to red fluorescence and separated using a high-speed cell-sorter for further processing. This novel reporter system and vector were successfully validated by shotgun library construction, cloned sequence isolation, PCR amplification and DNA sequencing of cloned inserts from bacteria after cell-sorting. This simple, robust system can also be adapted for diverse biosensor assays and is amenable to miniaturization. We demonstrated that dual-fluorescence reporting coupled with high-speed cell-sorting provides a more efficient alternative to traditional methods of clone isolation.     

Global cell sorting is mediated by local cell-cell interactions in the C. elegans embryo

The Caenorhabditis elegans embryo achieves pattern formation by sorting cells into coherent regions before morphogenesis is initiated. The sorting of cells is coupled to their fate. Cells move extensively relative to each other to reach their correct position in the body plan. Analyzing the mechanism of cell sorting in in vitro culture experiments using 4D microscopy, we show that all AB-derived cells sort only according to their local neighbors, and that all cells are able to communicate with each other. The directions of cell movement do not depend on a cellular polarity but only on local cell-cell interactions; in experimental situations, this allows even the reversal of the polarity of whole regions of the embryo. The work defines a new mechanism of pattern formation we call "cell focusing".     

Continuous dielectrophoretic separation of cell mixtures

Use of stream-centered dielectrophoresis (1–4) produced continuous separations on three cell mixtures (1)Chlorella vulgaris withNetrium digitus, (2)Ankistrodesmus falcatus withStaurastrum gracile, and (3)Saccharomyces cerevisiae withNetrium digitus. Maximal separations were obtained for these mixtures of live cells at 100 kHz, 600 kHz, and 2.0 MHz, respectively. The technique was restricted to a frequency range of 0.01–32 MHz, and to suspensions of low conductivity in which microorganisms such as these algae and yeast are tolerant. Extension, however, to cellular organisms requiring higher osmolarity is readily feasible through the use of nonionic solutes such as sucrose, mannose, glycine, etc.     

Cadherin-mediated cell sorting not determined by binding or adhesion specificity.

Cadherin adhesion molecules play important roles in the establishment of tissue boundaries. Cells expressing different cadherins sort out from each other in cell aggregation assays. To determine the contribution of cadherin binding and adhesion specificity to the sorting process, we examined the adhesion of cells to different purified cadherin proteins. Chinese hamster ovary cell lines expressing one of four different cadherins were allowed to bind to the purified cadherin extracellular domains of either human E-cadherin or Xenopus C-cadherin, and the specificity of adhesion was compared with cell-sorting assays. None of the different cadherin-expressing cells exhibited any adhesive specificity toward either of the two purified cadherin substrates, even though these cadherins differ considerably in their primary sequence. In addition, all cells exhibited similar strengthening of adhesion on both substrates. However, this lack of adhesive specificity did not determine whether different cadherin-expressing cells would sort from each other, and the tendency to sort was not predictable by the extent of sequence diversity in their extracellular domains. These results show that cadherins are far more promiscuous in their adhesive-binding capacity than had been expected and that the ability to sort out must be determined by mechanisms other than simple adhesive-binding specificity.     

Separation of active and inactive fractions from starved culture of Vibrio parahaemolyticus by density dependent cell sorting

The co-existence of physiologically different cells in bacterial cultures is a general phenomenon. We have examined the applicability of the density dependent cell sorting (DDCS) method to separate subpopulations from a long-term starvation culture of Vibrio parahaemolyticus. The cells were subjected to Percoll density gradient and separated into 12 fractions of different buoyant densities, followed by measuring the cell numbers, culturability, respiratory activity and leucine incorporation activity. While more than 78% of cells were in lighter fractions, about 95% of culturable cells were present in heavier fractions. The high-density subpopulations also had high proportion of cells capable of forming formazan granules. Although this was accompanied by the cell specific INT-reduction rate, both leucine incorporation rates and INT-reduction rates per cell had a peak at mid-density fraction. The present results indicated that DDCS could be used to separate subpopulations of different physiological conditions.     

Efficient enrichment of undifferentiated GFR alpha 1+ spermatogonia from immature rat testis by magnetic activated cell sorting

Spermatogonial stem cells (SSCs) are a documented source for adult multipotent stem cells. Thus, the isolation of SSCs is of great interest. However, the isolation of spermatogonia from mammalian testes is difficult because of their low total numbers and the lack of well-characterized cell surface markers. Glial-cell-derived neurotrophic factor family receptor alpha-1 (GFRα1) is expressed on undifferentiated mouse spermatogonia (including SSCs) and plays a crucial role, in rodents, for the maintenance of SSCs mediated by the Sertoli cell product GDNF. The present study has aimed to optimize the sorting efficiency and total cell yield of magnetic activated cell sorting (MACS) with anti-GFRα1 antibodies. Because of the technical limitations intrinsic to the magnetic columns, various sorting setups and strategies were compared. Use of Mini-MACS (MS) columns for single cell suspensions from 7-day-old rat testes resulted in a three-fold enrichment of GFRα1-positive cells in sorted fractions versus presorted fractions. However, with this method, only 1.77% of cells loaded onto the column were recovered in the sorted fraction. A sequential two-step sorting approach did not improve this poor yield. We therefore evaluated cell separation by using larger volume Midi-MACS (LS) columns. Enrichment of GFRα1-positive cells in sorted fractions was four-fold, and 14.5% of cells loaded onto the column were directed to the sorted fraction. With this method, approximately half of all GFRα1-positive cells present in the sample were found in the sorted fraction. We conclude that GFRα1 serves as a suitable surface marker for the enrichment of rat spermatogonia, and that the large-volume Midi-MACS separation system is superior to the routinely used small-volume Mini-MACS separation system. This work was financially supported by startup funds from the University Münster, NIH grant U54 HD 008610, Center grant, project 1 (to S.S.), a doctoral scholarship from the Ernst Schering Research Foundation (to K.G.), and a Young Investigator Grant from the Lance Armstrong Foundation (to J.E.).     

Lentivirus‐mediated bifunctional cell labeling for in vivo melanoma study

Lentiviral vectors (LVs) are capable of labeling a broad spectrum of cell types, achieving stable expression of transgenes. However, for in vivo studies, the duration of marker gene expression has been highly variable. We have developed a series of LVs harboring different promoters for expressing reporter gene in mouse cells. Long‐term culture and colony formation of several LV‐labeled mouse melanoma cells showed that promoters derived from mammalian house‐keeping genes, especially those encoding RNA polymerase II (Pol2) and ferritin (FerH), provided the highest consistency for reporter expression. For in vivo studies, primary B16BL6 mouse melanoma were infected with LVs whose luciferase–green fluorescence protein fusion gene (Luc/GFP) was driven by either Pol2 or FerH promoters. When transplanted into syngeneic C57BL/6 mice, Luc/GFP‐labeled B16BL6 mouse melanoma cells can be monitored by bioluminescence imaging in vivo, and GFP‐positive cells can be isolated from the tumors by fluorescence‐activated cell sorter. Pol2‐Luc/GFP labeling, while lower in activity, was more sustainable than FerH‐Luc/GFP labeling in B16BL6 over consecutive passages into mice. We conclude that Pol‐2‐Luc/GFP labeling allows long‐term in vivo monitoring and tumor cell isolation in immunocompetent mouse melanoma models.     

Megakaryocyte cell sorting from diosgenin-differentiated human erythroleukemia cells by sedimentation field-flow fractionation

Anticancer differentiation therapy could be one strategy to stop cancer cell proliferation. Human erythroleukemia (HEL) cell line, incubated with 10 microM diosgenin, underwent megakaryocytic differentiation. Thus, the association diosgenin/HEL could be used as a model of chemically induced cellular differentiation and anticancer treatment. The goal of this work was to determine the capacity of sedimentation field-flow fractionation (SdFFF) to sort megakaryocytic differentiated cells. SdFFF cell sorting was associated with cellular characterization methods to calibrate specific elution profiles. As demonstrated by cell size measurement methods, cellular morphology, ploidy, and phenotype, we obtained an enriched, sterile, viable, and functional fraction of megakaryocytic cells. Thus, SdFFF is proposed as a routine method to prepare differentiated cells that will be further used to better understand the megakaryocytic differentiation process.     

Dictyostelium mucoroides cells exhibit cell cycle-dependent sorting behavior as observed in D. discoideum development

Evidence has been obtained indicating that the cell's position in the cell cycle at the onset of starvation is a naturally occurring variable closely involved in the subsequent sorting and pattern formation during the development of Dictyostelium discoideum Ax2. It is of interest to know whether a similar phenomenon is also noticed in species other than D. discoideum and also without any treatment of cells for cell synchronization. For this, the sorting behavior of D. mucoroides-7 ( Dm7 ) cells and its relation to the cell-cycle phase at the onset of starvation were analyzed, using non-synchronized Dm7 cells pulse-labeled with 5'-bromo-2-deoxyuridine (BrdU). The results demonstrate that Dm7 cells starved at the early G2 phase aggregate most rapidly, but are eventually sorted out to the posterior prespore zone of migrating slugs. In contrast, cells starved at the mid late G2 phase exhibited slower aggregation, but were sorted out to the anterior zone (tip), this being basically similar to the sorting behavior of D. discoideum cells. Measurements of cell numbers and nuclearity provided evidence that approximately 80% of cells progressed their cell-cycle after the formation of multicellular structures (mounds), probably coupling with prespore differentiation as in the case of D. discoideum . Thus, cell cycle-dependent sorting during Dictyostelium development is most likely to be a common phenomenon in different species.     

不同培养基对流式细胞仪分选外周血T细胞的影响

摘要 目的：通过探讨用于流式分选的T细胞体外扩增的无血清培养基,提高过继细胞的增殖能力和活性。方法：采用人外周血淋巴细胞分离管制备外周血单个核细胞,再用流式细胞分选仪从6例健康志愿者的外周血单个核细胞中分选CD3+T细胞到4种常用的培养基中：X-VIVO 15、KBM 581、TexMACS GMP和10 % FBS/1640,观察并记录培养细胞的状态和体外增殖能力。于第3天,第6天和第8天,通过胎盼蓝染色后进行活细胞计数。于第8天用凋亡试剂盒检测扩增细胞的凋亡情况,并用流式细胞分析仪检测细胞的免疫表型。结果：X-VIVO 15、TexMACS GMP和10 % FBS/1640作为流式细胞分选的接收液仅少量细胞碎片,而分选在KBM 581的细胞大量死亡,显著高于X-VIVO 15组（P<0.05）。X-VIVO 15中扩增的细胞数量最多,增殖检测结果显示活细胞在X-VIVO 15中快速增殖且细胞凋亡率显著低于KBM 581 和 TexMACS GMP（P<0.05）。4种培养基扩增的细胞主要呈现效应记忆型。其中,X-VIVO 15中效应记忆型T细胞比例显著高于TexMACS GMP（P<0.05）。TexMACS中效应细胞比例显著高于10 % FBS/1640（P<0.05）。结论：X-VIVO 15无血清培养基扩增流式分选的T细胞具有高增殖能力、细胞活性和记忆表型,适用于经流式分选后细胞的体外扩增。     

Flow sorting of tumor cells for morphometric analysis,particularly of rare cells

Using flow cytometric DNA measurement and sorting combined with morphometric light microscopy, different groups of cells were studied in a human melanoma pleural effusion, a human melanoma lymph node metastasis and a mouse tumor, as well as in normal reference tissues. Beside cells of the predominant tumor cell population, three types of rare tumor cells were studied after enrichment by sorting: a) giant cells from the >8c region, comprising about 5% of the tumor cells, b) binucleated and multinucleated cells with unequal nuclear sizes within the same cell, found at frequencies of about 1.5%, and c) <2c cells which were derived from the so-called “debris”-region of the DNA histogram, found at frequencies of about 1 to 6%. All these rare cells were found only in the malignant tumors and not in the benign reference tissues. Morphometry showed that the increase in the cellular DNA content in the different fractions of tumor cells was combined with an increase in the cellular and nuclear sizes. However, the n/c-ratio was constant in the whole range of tumor cell fractions, including the fractions from the the <2c and the >8c regions. The n/c-ratio of the <2c cells and giant cells differed from that of corresponding normal cells underlining their origin from the predominant tumor cell population. The possible linkage between the occurrence of the three rare cell types and genetic instability of tumors related to faulty nucleus and cell division is discussed.