Cytoskeleton components are found to be severely affected by microgravity. Among all of the cytoskeleton components; notably microtubules (MT), intermediate filaments (IF) and microfilaments (MF), become disorganized. The cytoskeleton happens to reorganize after a time in microgravity 20 to 72 hours, but does not always seem to acquire the organization in the same configuration that it was in before. It has been revealed in n breast cancer cells that the peri-nuclear cyto-keratin network and chromatin structure were comparatively looser in microgravity. An experiment in the study on human renal cells in space in a microgravity environment was taken under investigation for gene expression. It was revealed that more than 1,632 genes changed their expression and that included huge changes in transcription factors (Hammond et al., 1999).
"The genes whose expression experienced the most alterations included adhesion molecules, apoptosis genes, cytoskeletal proteins, intracellular signalling proteins, receptors, transcriptions factors, differentiation mediators, drug metabolizing proteins, select heat shock proteins and elements of the electron transport chain".
Based on the published study, Effect of microgravity on cell cytoskeleton and embryogenesis by Susan J crowford-Young, it can be said that quite a good amount of work has been done on the influence of microgravity on microtubules and there were quite noticeable differences that were observed in the organization of patterns in 1G earth gravity and then in microgravity. In microgravity, microtubules in vitro had grown and organized in a homogenous or random pattern. While in 1G they grew and then spontaneously organized into a striped pattern Fig. 2B (Papaseit et al., 2000). The striped patterning have been shown to consist of microtubule bundles oriented at 45o and 135o from the horizontal direction in 1G. Pattern formation seemed to occur at different scales 0.5 mm wide stripes that contained microtubule stripes that were separated by a distance of 100 µm and did contain stripes 20 µm in width. That specific organization did not happen to occur in microgravity. In its place, microtubules in vitro had been shown to grow in a quite random fashion. Microtubules specifically grew or to be clearer, polymerized into long tubular polymers that consisted of alpha- and beta-tubulin dimers that bind together in a typically specific orientation. The icrotubule polymerization is equilibrium chemical reaction- diffusion process. The microtubules are found to be continuously forming and disintegrating in an order that when a microtubule depolymerizes it leaves behind its own components to build another polymerized microtubule. The microtubule polymerization process is known to be affected by gravity as there is more drift in the vertical direction as compared to lateral directions (Portet and Turzynski, 2003). The output of equilibrium chemical reaction underwent a bifurcation, which created the observed patterning of microtubule formation in 1G earth normal gravity level. Microfilaments were found to link to the microtubule network in vivo in order to form a strong stable tensegrity structure. Microfilaments were found to be altered in microgravity and also in microtubules. Microtubules may get typically stiffened against buckling via attachment to intermediate filaments in vivo. Intermediate filaments are also found to form in an out of equilibrium chemical reaction (Goldman et al., 1999) and can get affected in a similar manner by changes in gravity level.
In the cells, other vectors besides gravity, such as electric fields and Marangoni convection may also affect the formation of microtubules.
There is a hypothesis that says that the microtubules form an electric field as they polymerize and if they do so they will be affected by each other's electric field which might cause, the pattern formation. This could be the reason and provide an answer as to why cells can still live and grow in microgravity. Microtubules happen to get affected by magnetic fields and they are found to be forming patterns according to the direction of the field (Glade and Tabony, 2005). Similarities have been found recently during the course of the experiment between the effects on the grey crescent formation in amphibian eggs produced by UV radiation, and also the role of the grey crescent in axis formation and microgravity.
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