No abstract

Because cells are sensitive to mechanical forces, weightlessness might act on stress-dependent cell changes. We hypothesized that the integration of environmental factors might induce specific cytoskeletal architecture patterns, characterized by quantitative image analysis. Human breast cancer cells MCF-7, flown in space in a photon capsule, were fixed after 1.5, 22, and 48 h in orbit. Cells subjected to weightlessness were compared with 1g in-flight and ground controls. Postflight, fluorescent labelings were performed to visualize cell proliferation (Ki-67), signal transduction (phosphotyrosine), three cytoskeleton components (microtubules, microfilaments, and intermediate filaments), and chromatin structure. Confocal microscopy and image analysis were used to quantify cycling cells and mitosis, modifications of the cytokeratin network, and chromatin structure. In weightlessness, phosphotyrosine signal transduction was lower, more cells were cycling, and mitosis was prolonged. Finally, cell proliferation was reduced as a consequence of a cell-cycle blockade. Microtubules were altered in many cells. The perinuclear cytokeratin network was more loosely 'woven', and chromatin structure was modified. The prolongaion of mitosis can be explained by an alteration of microtubule self-organization in weightlessness, involving reaction-diffusion processes. The loosening of the perinuclear cytokeratin network and modification of chromatin distribution are in agreement with basic predictions of cellular tensegrity.

Genome-wide transcriptional profiling shows that reducing gravity levels during Drosophila metamorphosis in the International Space Station (ISS) causes important alterations in gene expression: a large set of differentially expressed genes (DEGs) are observed compared to 1g controls. However, the preparation procedures for spaceflight and the nonideal environmental conditions on board the ISS subject the organisms to additional environmental stresses that demonstrably affect gene expression. Simulated microgravity experiments performed on the ground, under ideal conditions for the flies, using the random position machine (RPM), show much more subtle effects on gene expression. However, when the ground experiments are repeated under conditions designed to reproduce the additional environmental stresses imposed by spaceflight procedures, 79% of the DEGs detected in the ISS are reproduced by the RPM experiment. Gene ontology analysis of them shows they are genes that affect respiratory activity, developmental processes and stress-related changes. Here, we analyse the effects of microgravity on gene expression in relation to the environmental stresses imposed by spaceflight. Analysis using 'gene expression dynamics inspector' (GEDI) self-organizing maps reveals a subtle response of the transcriptome to microgravity. Remarkably, hypergravity simulation induces similar response of the transcriptome, but in the opposite direction, i.e. the genes promoted under microgravity are usually suppressed under hypergravity. These results suggest that the transcriptome is finely tuned to normal gravity and that microgravity, together with environmental constraints associated with space experiments, can have profound effects on gene expression.

No abstract

Because cells are sensitive to mechanical forces, weightlessness might act on stress‐dependent cell changes. We hypothesized that the integration of environmental factors might induce specific cytoskeletal architecture patterns, characterized by quantitative image analysis. Human breast cancer cells MCF‐7, flown in space in a photon capsule, were fixed after 1.5, 22, and 48 h in orbit. Cells subjected to weightlessness were compared with 1 g in‐flight and ground controls. Postflight, fluorescent labelings were performed to visualize cell proliferation (Ki‐67), signal transduction (phosphotyrosine), three cytoskeleton components (microtubules, microfilaments, and intermediate filaments), and chromatin structure. Confocal microscopy and image analysis were used to quantify cycling cells and mitosis, modifications of the cytokeratin network, and chromatin structure. In weightlessness, phosphotyrosine signal transduction was lower, more cells were cycling, and mitosis was prolonged. Finally, cell proliferation was reduced as a consequence of a cell‐cycle blockade. Microtubules were altered in many cells. The perinuclear cytokeratin network was more loosely ‘woven’, and chromatin structure was modified. The prolongaion of mitosis can be explained by an alteration of microtubule self‐organization in weightlessness, involving reaction‐diffusion processes. The loosening of the perinuclear cytokeratin network and modification of chromatin distribution are in agreement with basic predictions of cellular tensegrity.