High-speed photodamage cell selection using bromodeoxyuridine/Hoechst 33342 photosensitized cell killing

Distinct stem-like cell populations facilitate functional regeneration of the Cladonema medusa tentacle

Blastema formation is a crucial process that provides a cellular source for regenerating tissues and organs. While bilaterians have diversified blastema formation methods, its mechanisms in non-bilaterians remain poorly understood. Cnidarian jellyfish, or medusae, represent early-branching metazoans that exhibit complex morphology and possess defined appendage structures highlighted by tentacles with stinging cells (nematocytes). Here, we investigate the mechanisms of tentacle regeneration, using the hydrozoan jellyfish Cladonema pacificum. We show that proliferative cells accumulate at the tentacle amputation site and form a blastema composed of cells with stem cell morphology. Nucleoside pulse-chase experiments indicate that most repair-specific proliferative cells (RSPCs) in the blastema are distinct from resident stem cells. We further demonstrate that resident stem cells control nematogenesis and tentacle elongation during both homeostasis and regeneration as homeostatic stem cells, while RSPCs preferentially differentiate into epithelial cells in the newly formed tentacle, analogous to lineage-restricted stem/progenitor cells observed in salamander limbs. Taken together, our findings propose a regeneration mechanism that utilizes both resident homeostatic stem cells (RHSCs) and RSPCs, which in conjunction efficiently enable functional appendage regeneration, and provide novel insight into the diversification of blastema formation across animal evolution.

High-speed cell sorting

A flow cytometer has the ability to analyze several thousand cells per second. This is particularly valuable for the detection of rare events. For many biological and clinical applications, cells must be isolated on the basis of multiple quantitative properties. This need is ideally met by the analytical power of flow cytometry, which provides the front-end selection mechanism for cell sorting. In essence, cell sorting represents real-time data classification coupled with actual physical isolation of cells with the properties of interest. This unit discusses the principles and practices of operating a cell sorter to maximize the sorting rate, including the trade-offs between speed and resolution.

Development of a clinically applicable high-speed flow cytometer for the isolation of transplantable human hematopoietic stem cells

A high-speed cell sorter capable of a throughput speed 4-5-fold greater than commercially available systems was developed and evaluated as a processing tool for isolating purified hematopoietic stem cell grafts. The clinical high-speed sorter (CHSS) serves as a single-pass, multiparameter processing tool that provides the means to isolate a highly purified population of cells from starting cell populations with extremely low frequencies. The sorter incorporates environmental barriers to create a sterile environment for cell processing. Monoclonal antibodies and reagents produced under good manufacturing practices (GMP) are used to isolate hematopoietic stem cells by means of the CHSS. Using this technology, the CD34+Thy-1+Lin- hematopoietic stem cell population has been isolated from normal adult bone marrow and mobilized peripheral blood. The sorted cells have been shown to be sterile and viable and to retain hematopoietic function.

High-speed photodamage cell selection using a frequency-doubled argon ion laser

A flow cytometer was developed for the high-speed "sorting" of desired cells by selectively irradiating (zapping) the undesired cells from a population. After previous efforts to photoinactivate cells with photosensitizers had failed, it was decided to exploit the photosensitivity of the cell's DNA at 257 nm. It was shown that a 257 nm laser output power of 20-100 mW was sufficient to induce a 4.5 log cell kill after the cells were processed through a focused 257 nm laser beam. Experiments proved that the photodamage flow cytometer (ZAPPER) could selectively photoinactivate cells at rates over 22,000 events/s, and selection purities ranged from 81% to 100%. The yields of the desired cells depended on the selection mode. In the Enrichment mode, the zap laser was not aimed at the jet, and only undesired cells were exposed to a brief ultraviolet (UV) pulse after modulation of the UV laser beam. The yields of desired cells ranged from 95% to 105%. In the Purge mode, the zap laser beam was aimed onto the jet, and only desired cells were allowed to pass after deflection of the UV laser beam; the yields of desired cells ranged from 12% to 52%. The cause of the reduced yields in the PURGE mode was traced to the fact that the Electro-Optic Modulator was used to modulate the zap laser proved too slow for the intended application. The lifetime of the frequency-doubling crystal used for the generation of the 257 nm beam was found to be limited to several days.(ABSTRACT TRUNCATED AT 250 WORDS)

Coincidence in high-speed flow cytometry: models and measurements

In flow cytometry, the coincident arrival of particles becomes a major problem when high sample rates are required. For the development of our high-speed photodamage flow cytometer (ZAPPER), it was of importance to understand the behavior of cells at flow rates of around 50,000-250,000 event/s. We developed and compared two models that describe the relation between the real cell rate and the detectable single cell rate. Both the Computer Simulation model and the Input/Output Device model show distinct optima for the cell rate. The models were compared to measurements performed on the ZAPPER-prototype. Fits of the two models to the experimental data were excellent for cycle times of 4 and 15 microseconds and acceptable for a 2 microseconds cycle time. A third model (Mercer WB, Rev. Sci. Instr. 37:1515-1521,1966) could be fitted to the experimental data, after the proportionality constant k was adapted to the experimental data. At a yield of detectable single cells of 70%, the maximum cell rates are 180,000, 100,000, and 40,000 cells/s for cycle times of 2, 4, and 15 microseconds, respectively. Based on these results we can now select an optimal cell rate for analysis and sorting based on criteria such as accepted cell loss. In addition, the advantages of reducing the cycle time can now be evaluated with respect to the costs of that modification.

A new principle of cell sorting by using selective electroporation in a modified flow cytometer

When a strong electric field pulse of a few microseconds is applied to biological cells, small pores are formed in the cell membranes; this process is called electroporation. At high field strengths and/or long pulse durations the membranes will be damaged permanently. This eventually leads to cell kill. We have developed a modified flow cytometer in which one can electroporate individual cells selected by optical analysis. The first experiments with this flow cytometer were designed to use it as a damaging sorter; we used electric pulses of 10 microseconds and resulting field strengths of 2.0 and 3.2 x 10(6) V/m to kill K562 cells and lymphocytes respectively. The hydrodynamically focused cells are first optically analyzed in the usual way in a square flow channel. At the end of this channel the cells are forced to flow through a small Coulter orifice, into a wider region. If optical analysis indicates that a cell is unwanted, the cell is killed by applying a strong electric field across the Coulter orifice. The wanted living cells can be subsequently separated from the dead cells and cell fragments by a method suitable for the particular application (e.g., centrifugation, cell growth, density gradient, etc.). The results of these first experiments demonstrate that by using very simple equipment, sorting by selective killing with electric fields is possible at rates of 1,000 cells/s with a purity of the sorted fraction of 99.9%.

Parallel processing data acquisition system for multilaser flow cytometry and cell sorting

This report describes the data acquisition electronics for a flow cytometer. The design differs from most instruments in that the signals from a large number of detectors are processed in parallel. Each of the input channels is capable of autonomously measuring and digitizing the fluorescence signals. The digitized values that belong to one particle are collected by digital circuitry and are presented as a compact data package on a special bus. In addition to the pulse values, the data package contains a time marker, information needed for sort decisions, and an error detection code. Specially designed electronic modules that read the information from the bus can take complex multiparameter sort decisions at a very high speed. All events can also be recorded as data lists by a computer. The lists can be used to reconstruct a sort or analysis run. The raw data lists can also be reduced to kinetic curves and/or (gated) multivariate histograms. As a result of the applied scheme of parallel pulse processing, the dead time of the system is independent of the number of parameters measured and the number and time separation of the excitation beams. The instrument has a cycle time of 5 microseconds, which corresponds to a throughput rate of 2 x 10(5) events/s. At this rate, the incidence of correlation errors is well below 1 in 10(8) analyzed particles. The system has proved to be reliable and convenient to use in a variety of experiments. Its high speed and low error rate make it well suited for high-resolution measurements, rare-event analysis, kinetic measurements, and high-speed cell sorting.