Time Course Of Cellular Responses Research Articles

Multimodal single-cell analysis reveals distinct radioresistant stem-like and progenitor cell populations in murine glioma.

Radiation therapy is part of the standard of care for gliomas and kills a subset of tumor cells, while also altering the tumor microenvironment. Tumor cells with stem‐like properties preferentially survive radiation and give rise to glioma recurrence. Various techniques for enriching and quantifying cells with stem‐like properties have been used, including the fluorescence activated cell sorting (FACS)‐based side population (SP) assay, which is a functional assay that enriches for stem‐like tumor cells. In these analyses, mouse models of glioma have been used to understand the biology of this disease and therapeutic responses, including the radiation response. We present combined SP analysis and single‐cell RNA sequencing of genetically‐engineered mouse models of glioma to show a time course of cellular response to radiation. We identify and characterize two distinct tumor cell populations that are inherently radioresistant and also distinct effects of radiation on immune cell populations within the tumor microenvironment.

Cells Go Solo

[ Read the Introduction to this Special Section ][1] ![Figure][2] CREDIT: DINA FADDAH AND RUDOLF JAENISCH/THE WHITEHEAD INSTITUTE FOR BIOMEDICAL RESEARCH The scientific literature contains an enormous body of work in which large numbers of cells have been broken open and homogenized to prepare samples for biochemical characterization and, certainly, much has been learned from such studies. But more recently, it has become possible to monitor events in single cells, thus allowing investigators to test whether existing “averaged” readings of the state of many cells from traditional large-scale assays accurately represent the behavior of the individual cells being studied. Such single-cell measurements are providing a wealth of information—sometimes unanticipated and often previously obscured—about how cells respond to perturbations or signals. In this special issue, three Reviews provide examples of fundamental insights into cellular regulation that are revealed when it is possible to measure enzymatic activity, transcriptional responses, or the metabolic state in individual cells. An obvious advantage of single-cell measurements is the ability to measure variations or “noise” in the responses of the individual cells to similar or identical conditions. In many instances, it is possible to monitor the time course of cellular responses. Gene transcription can be particularly noisy, with bursts of RNA synthesis occurring in some cells but not others of the same population. Thus, fundamental questions arise about the nature of these systems. Perhaps variation in response is advantageous in conserving resources or in assuring that some cells survive in a changing environment. Or it may be that biophysical constraints of small numbers of molecules and the characteristics of the enzymes at work dictate such variability as unavoidable. Sanchez and Golding review recent work in model systems, from bacteria to animal cells, that attempts to resolve whether the kinetics of transcription are encoded in the architecture of promoter sequences in DNA—and might therefore vary throughout the genome—or are determined by physical or biophysical properties that would impose more global constraints throughout the cell. Levine et al. explore another previously hidden phenomenon. Continuous measurements of protein activation show that many undergo asynchronous pulsatile responses, which are obscured in average measurements from a population of cells. They discuss how cellular circuits are wired to produce such responses and what the advantages of such control systems might be. Zenobi highlights methodological advances, particularly in mass spectrometry, that are enabling quantitation of the abundance of molecular components of single cells. Challenges abound for the goal of making simultaneous measurements to characterize the rapid ly changing metabolic state of individual cells. But the promise of new insights across a broad range of disciplines is sustaining a steady effort to tap into the large store of new knowledge lying hidden within the confines of single cells. [1]: http://www.sciencemag.org/content/342/6163/1187 [2]: pending:yes

The Hydrolysis of Extracellular Adenine Nucleotides by Arterial Smooth Muscle Cells: Regulation of adenosine production at the cell surface

The extracellular reaction sequence ATP----ADP----AMP----adenosine participates in regulating the time course of cellular response during crisis or signaling events, such as thrombus formation or neurotransmission. We have investigated the whole time course of hydrolysis of ATP to adenosine by recirculating adenine nucleotide substrates over smooth muscle cells attached to polystyrene beads. Kinetic parameters were estimated for each reaction by fitting observed time courses to models of the pathway. In spite of the inhibition of 5'-nucleotidase by ADP, adenosine was produced very rapidly by smooth muscle cells. Comparisons of the apparent Km values of ADPase and 5'-nucleotidase (determined from experiments in which each substrate was used as the initial substrate with Km values observed when each substrate was supplied from the upstream reaction) suggest that the local concentrations of substrate supplied from the preceding reactions are very much higher than those in the bulk phase. This enhancement of efficiency overcomes the effect of the feed-forward inhibition to give rise to very rapid adenosine production from ADP or ATP. These observations are in marked contrast to our previous findings with endothelial cells (Gordon, E. L., Pearson, J. D., and Slakey, L. L. (1986) J. Biol. Chem. 261, 15496-15504), on which feed-forward inhibition causes a profound lag in adenosine production from adenine nucleotides and on which there are no apparent surface effects on substrate delivery.

The time course of cellular responses to iontophoretically applied drugs

Explicit expressions are derived giving a measure of the time course of responses to iontophoretic application of drugs or neurotransmitters. Cases treated include receptors on a line, a plane, and a sphere, effect of membrane capacitance, and binding of the drug to a surface, all of which give responses slower than those predicted on the usual “point receptor” assumption. Chemical reaction, for instance hydrolysis of the drug in the medium or on a surface, tends to shorten responses. Threshold and saturation non-linearities are also considered. It is concluded that agreement of experimental results with the “point receptor” time course is rather unlikely, although discrepancies will be masked if the distance between the iontophoretic source and the tissue is not measured but estimated from the responses.