IntroductionThe cytoskeleton was found very late until the use of glutaraldehyde at room temperature in 1960s, whichmake it observable with the electron microscope. It consists of a structuralsystem called cytoskeletal system, and it is named three intracellular systemstogether with intracellular genetic systems and cell membranes system. In most mammals, three kinds of filaments in cells make up thecytoskeleton system: Microtubules, Microfilaments and Intermediate filaments (Figure1). Then dimension of microtubules is normally 25nm, the largest one, whichtakes longest time to growth and it is comparatively steady than the others.And microtubules build the main structure of cytoskeleton, supporting themicrofilaments and intermediate filaments.
Microfilaments have the smallestdimension (about 7nm) among them, and mainly make up from actin, so are namedactin filaments sometimes. The active actin filaments are formed with a complexcycle, including many cooperation of various types of actin proteins. Theformation is assisted by a wild range of actin-binding different proteins andsometimes overlapping activities (Jockusch, 2017). The diameter ofintermediate filaments is between microtubules and intermediate filaments,commonly 10nm. The cytoskeleton’s varied functions depend on the behaviour ofthree families of filaments, such as transformation, motility, growth anddifferentiation (Alberts, 2008).Fig. 1.Diagrams of the cytoskeleton systemThe cytoskeleton supports the cell structure anddetermine the shape.
It not only determines the mechanical behaviours and stabilityof cells, but also controls the motility and deformation of cells and helpcells to perform various biological functions such as transport of biologicalmolecules.Recently, many important events about cell indifferent time and space scales have been discovered, including the cellularmechanotransduction. Briefly, thecellular mechanotransduction is a big discovery in the biology, and analysis ofthis subject need to understand ‘Stretch-activated ion channels, caveolae,integrins, cadherins, growth factor receptors, myosin motors, cytoskeletalfilaments, nuclei, extracellular matrix, and numerous other structures andsignaling molecules’ (Ingber, 2006).And it is a process that outside signal transmits to intracellular componentswhile cell contacts the environment, which influences the growth/depolymerisationand cross-linking/unbinding of cytoskeleton. This process consists of a rangeof dynamic response. In contrast, this dynamic response will make an effect onthe environment and both of them achieve a dynamic balance eventually. Cellularmechanotransduction has a deep influence on cell and biodiversity, andexploring and discovering cellular mechanotransduction not only promote thedevelopment of biomedicine, but also like the goal scientists want to achieve. Thestudy in cellular mechanotransduction still has numbers of problems to be solved,but the important role cytoskeleton plays in the cellular mechanotransduction iswidely recognised.
Besides that, cytoskeletonnetwork is a kind of spatial flexible structure that can be simulated bymechanical model. Cytoskeleton is an extremely complexbiomolecular system in which molecular-scale components form a mesoscopic scalestructure together, and mesoscopic scale structure couples with each other toform a continuous network. Some researchers use fractal dimension method to describethis continuous and inhomogeneous structure and this method will be talkedlater. From the viewpoint of bionics, thecytoskeleton network has certain reference value for the study of spatialstructure. Scientists can find more effective method to support a structurewith limited materials by simulating the cytoskeleton network directly insteadof using computers to explore.
Researchers carried out a large number of experimentalstudies to approach the truth of cytoskeleton gradually, and this article isaimed at review and summarize some results. Due to the limited background andlevel of the author, this essay only talks about some experiments and simplytheoretical models. Some Dynamic Characteristics about Cytoskeleton and ExperimentsAs the cytoskeleton system includes three filamentsand they connect to each other to form a complex network in a nanometredimension, so it is different for researchers manipulate the cell directly.
Hencemany new experimental methods are used to discover the characteristics withparticular designed machines. Scientists usually mark the cytoskeleton networkwith immunofluorescence and then scanned by laser scanner to analyse thedistribution and density of cytoskeleton.Sonoporation is still a mystery to the cytoskeletonnetwork, which is how the cytoskeleton will behaviour like breakdown orreorganization under a certain strength of Sonoporation. Except that, theformation of pore by destroying the actin filaments or microtubules was studiedthrough various experiments, but is still undiscovered.
Zeghimi and his team did not study the formation ofpore but compared the Sonoporation samples with control samples to explore thesome dynamic response on Sonoporation. They cultured human glioblastoma cells (U-87 MG) as the samples and exposed them underultrasound environment. In addition, these cells were marked with immunofluorescenceand then scanned by laser scanner.
From the images shot by the laser scanner (Figure2), the difference between filaments network is very obvious as the latersamples’ cytoskeleton reorganized the actin and microtubules. From further comparison,this figure shows that the ‘combination of the ultrasound and microbubblesincrease the numbers of F-actin stress fibers’. (Zeghimi, 2014).
And after destroyed by ultrasound, the recovery of cytoskeleton is continuous andthe experimental samples (U-87 MG) has reorganized almost 92 percent proteincytoskeleton after one hour.Figure 2:Effect ofsonoporation on ACTIN and TUBULIN cytoskeleton in U-87 MG. White arrows showthe actin and tubulin network in control cells, while arrowhead designate the disorganizationof cytoskeleton immediately after sonoporation.Considering the recoveryof sample cells, they used inhibitors to stop the recovery process and observedthe transmit ratio of SYTOX® Green was greatly decreased for 87 percentage. Thisphenomenon can be viewed as an evidence on the transmit function ofcytoskeleton, but more researches are needed to prove this assumption. Fractal dimension is atheory which assume the detail parts change with the scale of measuring, and itwould be a great way to analyze complex space form.
Qian and her team quantifiedthe MC3T3-E1 cells cytoskeleton with the fractal dimension analysis undermicrogravity. Before their study, there are some research reported that thecytoskeleton is going to alter under the spaceflight or weightless environment,but the quantitative analysis had not been achieved. In this experiment, 3-D/2-DClinostats are used to simulate the weightless environment and operated in ahumidified incubator (5% CO 2 at 37 °C). Then using Leica TCS SP5 laserscanning to record the cellular cytoskeleton after cells are cultured in the 3-D/2-DClinostats for 24 and 48 hours. NIH software ImageJ is used to quantify thecytoskeleton images captured by Leica TCS SP5. In short, each complete cellimage see Figure 2 (a1) and (a2) is separated and translated into the 200 *200 pixel gray value see Figure 2 (b1) and (b2). Through the automaticthreshold function of ImageJ (process> binary> make binary), thegrayscale image is converted to two valued image (black and white), whichcontains only the contour information of the cytoskeleton as ROI see Figure 2(c1) and c2. Then, based on box counting, ImageJ automatically determines thesize of the cytoskeleton see Figure 2 (d1) and (d2).
The mean fractaldimension (D) of more than 10 cells was calculated and analyzed statistically.They found themicrogravity environment do influence the distribution of F-Actin within 24hours, but after 48 hours, the cytoskeleton can re-organize the structure andrecover to a common condition with the statistical data. However, the intensityof ?-actin mRNA expression is different from the F-actin. It increased after 24hours clinorotation to count the stress change, then the decrease shows theadaption is almost complete after 48 hours. These findings indicate the microgravitydoes limit damage to cytoskeleton with limit time and cells can recover fromthe damage but will take relatively long time, but the results about cellsexposed to microgravity for enough has not been confirmed. (A.
R.Qian, 2012)The mechanics of normalcells are different from cancer cells. Based on this principle, Shohreh and histeam intended to transform the cancer cells by restoring stiffness of abnormalcells. In this experiment, they chose actin cytoskeleton as the target torecover the elastic properties with the use of Lapatinib, a small molecule forinhibiting EGFR over-activity. The over-activity of EGFR in the cells can leadto the loss of mechanical properties like stiffness and adhesiveness because EGFRis similar as the signal that influences the cells. And the atomic forcemicroscopy was used to measure the mechanical properties with the formula: After treated by Lapatinib for 24 hours, themechanical properties were measured and analysed, so the following figure (Fig.
3) show the comparison between control cancer cells and Lapatinib about Young’sModules. And the Fig. 4 compare the actin filaments between two kinds of cells. Figure3. Young’s modules differenceFigure 4.The actinfilaments observed under the fluorescence microscopeThese two figuresshows that Lapatinib stopped the signal pathway of EGFR, and recover themechanical properties obviously (Shohreh Azadi, 2016).The mechanical properties including elasticity and adhesiveness influence cancercells metastasis, which will rise the generation speed of cancer cells. Now basedon the finding on Lapatinib, Lapatinib has been used in treating breast cancersin the USA.
But this results did not talk about the effect on Lapatinibfurther, like: will this molecular will decrease the growth speed of breastcancer cells or just make the cancer cell like the normal cells. This findingmay be a suggest that treat the cytoskeleton of cancer cells let them become orpartial become normal cells, as well as stop the relentless division and cancercells metastasis.