Plant organs can adopt a wide range of shapes, resulting from highly directional cell growth and divisions. We focus here on leaves and leaf-like organs in Arabidopsis and tomato, characterized by ...the formation of thin, flat laminae. Combining experimental approaches with 3D mechanical modeling, we provide evidence that leaf shape depends on cortical microtubule mediated cellulose deposition along the main predicted stress orientations, in particular, along the adaxial-abaxial axis in internal cell walls. This behavior can be explained by a mechanical feedback and has the potential to sustain and even amplify a preexisting degree of flatness, which in turn depends on genes involved in the control of organ polarity and leaf margin formation.
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•Microtubules and cellulose microfibrils align along the ad-abaxial direction•Microtubule-mediated cell growth anisotropy contributes to leaf flattening•Mechanical feedback accounts for microtubule alignments in the ad-abaxial direction•Final organ shape depends on the degree of initial asymmetry of primordia
How do leaves maintain highly directional cell growth and divisions to form thin, flat laminae? Zhao et al. show that microtubules and cellulose microfibrils align along the main stress direction of internal walls to mediate anisotropic growth. Microtubule-mediated mechanical feedback amplifies an initial asymmetry and maintains directional growth.
ABSTRACT
Translocation of the dense nucleus along a gravity vector initiates mechanical remodeling of a cell, but the underlying mechanisms of cytoskeletal network and focal adhesion complex (FAC) ...reorganization in a mammalian cell remain unclear. We quantified the remodeling of an MC3T3‐E1 cell placed in upward‐, downward‐, or edgeon‐orientated substrate. Nucleus longitudinal translocation presents a high value in downward orientation at 24 h or in edge‐on orientation at 72 h, which is consistent with orientation‐dependent distribution of perinuclear actin stress fibers and vimentin cords. Redistribution of total FAC area and fractionized super mature adhesion number coordinates this dependence at short duration. This orientation‐dependent remodeling is associated with nucleus flattering and lamin A/C phosphorylation. Actin depolymerization or Rho‐associated protein kinase signaling inhibition abolishes the orientation dependence of nucleus translocation, whereas tubulin polymerization inhibition or vimentin disruption reserves the dependence. A biomechanical model is therefore proposed for integrating the mechanosensing of nucleus translocation with cytoskeletal remodeling and FAC reorganization induced by a gravity vector.—Zhang, C., Zhou, L., Zhang, F., Lü, D., Li, N., Zheng, L., Xu, Y., Li, Z., Sun, S., Long, M. Mechanical remodeling of normally sized mammalian cells under a gravity vector. FASEB J. 31, 802–813 (2017). http://www.fasebj.org
Cell deformability is an important biomarker which can be used to distinguish and sort between healthy and cancer cells. In this paper, we presented a dissipative particle dynamics (DPD) model for ...investigating cell entry into micro-channels. The cell membrane is represented by a network of DPD particles (beads) connected by worm-like chain (WLC) springs, which is able to mimic the viscoelastic effect of the membrane. The entry process of benign breast epithelial cells (MCF-10A) and non-metastatic tumor breast cells (MCF-7) through a constricted micro-channel are comparatively investigated using this DPD model. It is shown that both the time histories of the cell displacement and the dynamic behaviors of cell entry agree with experimental observations. The entry time of MCF-10A cell is approximately four times of that of MCF-7 cell since MCF-10A cells are stiffer than MCF-7 cells. It is demonstrated that the presented DPD method is effective in modeling cell deformability, and the obtained results can be helpful in understanding how cells with different mechanical properties respond to physical loads.
Double-layered channels of sinusoid lumen and Disse space separated by fenestrated liver sinusoidal endothelial cells (LSECs) endow the unique mechanical environment of the liver sinusoid network, ...which further guarantees its biological function. It is also known that this mechanical environment changes dramatically under liver fibrosis and cirrhosis, including the reduced plasma penetration and metabolite exchange between the two flow channels and the reduced Disse space deformability. The squeezing of leukocytes through narrow sinusoid lumen also affects the mechanical environment of liver sinusoid. To date, the detailed flow-field profile of liver sinusoid is still far from clear due to experimental limitations. It also remains elusive whether and how the varied physical properties of the pathological liver sinusoid regulate the fluid flow characteristics. Here a numerical model based on the immersed boundary method was established, and the effects of Disse space and leukocyte elasticities, endothelium permeability, and sinusoidal stenosis degree on fluid flow as well as leukocyte trafficking were specified upon a mimic liver sinusoid structure. Results showed that endothelium permeability dominantly controlled the plasma penetration velocity across the endothelium, whereas leukocyte squeezing promoted local penetration and significantly regulated wall shear stress on hepatocytes, which was strongly related to the Disse space and leukocyte deformability. Permeability and elasticity cooperatively regulated the process of leukocytes trafficking through the liver sinusoid, especially for stiffer leukocytes. This study will offer new insights into deeper understanding of the elaborate mechanical features of liver sinusoid and corresponding biological function.
Abstract Malaria transmission-blocking vaccines (TBVs) are potentially helpful tools for malaria eradication. The standard membrane-feeding assay (SMFA) is considered one of the “gold standard” ...assays for TBV development. However, lack of consensus in reporting results from SMFA has made it very challenging to compare results from different studies. Two main readouts, % inhibition in mean oocyst count per mosquito (TRA) and % inhibition in prevalence of infected mosquitoes (TBA), have been used widely. In this study, we statistically modeled the oocyst data in SMFA using data from 105 independent feeding experiments including 9804 mosquitoes. The model was validated using an independent data set that included 10,790 mosquitoes from 110 feeding studies. The model delineates a relationship between TRA, the mean oocyst count in the control mosquitoes ( mo -contl), and TBA. While TRA was independent from mo -contl, TBA values changed depending on mo -contl. Regardless of monoclonal or polyclonal antibodies tested, there were strong concordances between observed TBA and predicted TBA based on the model using mo -contl and observed TRA. Simulations showed that SMFA with lower true control means had increased uncertainty in TRA estimates. The strong linkage between TBA, TRA and mo -contl inspired creation of a standardized TBA, a model-based TBA standardized to a target control mean, which allows comparison across multiple feeds regardless of mo -contl. This is the first study showing that the observed TBA can be reasonably predicted by mo -contl and the TRA of the test antibody using independent experimental data. This study indicates that TRA should be used to compare results from multiple feeds with different levels of mo -contl. If a measure of TBA is desired, it is better to report standardized TBA rather than observed TBA. These recommendations support rational comparisons of results from different studies, thus benefiting future TBV development.
Organs-on-chips composed of a porous membrane-separated, double-layered channels are used widely in elucidating the effects of cell co-culture and flow shear on biological functions. While the ...diversity of channel geometry and membrane permeability is applied, their quantitative correlation with flow features is still unclear. Immersed boundary methods (IBM) simulations and theoretical modelling were performed in this study. Numerical simulations showed that channel length, height and membrane permeability jointly regulated the flow features of flux, penetration velocity and wall shear stress (WSS). Increase of channel length, lower channel height or membrane permeability monotonically reduced the flow flux, velocity and WSS in upper channel before reaching a plateau. While the flow flux in lower channel monotonically increased with the increase of each factor, the WSS surprisingly exhibited a biphasic pattern with first increase and then decrease with increase of lower channel height. Moreover, the transition threshold of maximum WSS was sensitive to the channel length and membrane permeability. Theoretical modeling, integrating the transmembrane pressure difference and inlet flow flux with chip geometry and membrane permeability, was in good agreement with IBM simulations. These analyses provided theoretical bases for optimizing flow-specified chip design and evaluating flow microenvironments of in vivo tissue.
Graphic Abstract
Due to their extraordinary affinity for both water and oil, super‐amphiphilic materials have garnered considerable interest. A Na2Ti3O7 (NTO) film with super‐amphiphilic properties that enable water ...and oil miscibility is offered. Multiple nanofibrous 3D porous nanostructures compose the super‐amphiphilic NTO layer. Up to 32–36 times its weight, the film has a high absorption capacity for water and poly‐alpha‐olefin (PAO). The average miscibility ratio of water to oil in the film is ≈6:5. The discovery of NTO nanofibrous film's super‐amphiphilic behavior has significant implications for the development of superwetting materials and their potential applications in the oil emulsion purification and catalyst anchoring industries.
A Na2Ti3O7 (NTO) film composed of numerous nanofibrous into 3D porous nanostructures has super‐amphiphilic properties that enable water and oil miscibility. The film has a high absorption capacity for water and poly‐alpha‐olefin (PAO) up to 32–36 times its weight. The average miscibility ratio of water to oil in the film is ≈6:5.
Pfs230 is a leading malaria transmission blocking vaccine (TBV) candidate. Comprising 3135 amino acids (aa), the large size of Pfs230 necessitates the use of sub-fragments as vaccine immunogens. ...Therefore, determination of which regions induce functional antibody responses is essential. We previously reported that of 27 sub-fragments spanning the entire molecule, only five induced functional antibodies. A "functional" antibody is defined herein as one that inhibits Plasmodium falciparum parasite development in mosquitoes in a standard membrane-feeding assay (SMFA). These five sub-fragments were found within the aa 443-1274 range, and all contained aa 543-730. Here, we further pinpoint the location of epitopes within Pfs230 that are recognized by functional antibodies using antibody depletion and enrichment techniques. Functional epitopes were not found within the aa 918-1274 region. Within aa 443-917, further analysis showed the existence of functional epitopes not only within the aa 543-730 region but also outside of it. Affinity-purified antibodies using a synthetic peptide matching aa 543-588 showed activity in the SMFA. Immunization with a synthetic peptide comprising this segment, formulated either as a carrier-protein conjugate vaccine or with a liposomal vaccine adjuvant system, induced antibodies in mice that were functional in the SMFA. These findings provide key insights for Pfs230-based vaccine design and establish the feasibility for the use of synthetic peptide antigens for a malaria TBV.
The functional performance of the αI domain α7 helix in β2 integrin activation depends on the allostery of the α7 helix, which axially slides down; therefore, it is critical to elucidate what factors ...regulate the allostery. In this study, we determined that there were two conservative salt bridge interaction pairs that constrain both the upper and bottom ends of the α7 helix. Molecular dynamics (MD) simulations for three β2 integrin members, lymphocyte function‐associated antigen‐1 (LFA‐1; αLβ2), macrophage‐1 antigen (Mac‐1; αMβ2) and αxβ2, indicated that the magnitude of the salt bridge interaction is related to the stability of the αI domain and the strength of the corresponding force‐induced allostery. The disruption of the salt bridge interaction, especially with double mutations in both salt bridges, significantly reduced the force‐induced allostery time for all three members. The effects of salt bridge interactions of the αI domain α7 helix on β2 integrin conformational stability and allostery were experimentally validated using Mac‐1 constructs. The results demonstrated that salt bridge mutations did not alter the conformational state of Mac‐1, but they did increase the force‐induced ligand binding and shear resistance ability, which was consistent with MD simulations. This study offers new insight into the importance of salt bridge interaction constraints of the αI domain α7 helix and external force for β2 integrin function.
The effect of salt bridge interactions of β2 integrin α7 helix on force‐induced αI domain allostery and ligand binding. Release of salt bridge interaction constraints of the α7 helix resulted in higher freedom and greater allosteric movement of β2 integrin αI domain α7 helix under the same external force and time, which led to stronger ligand binding and shear resistance.
Effective malaria transmission-blocking vaccines (TBVs) can support malaria eradication programmes, and the standard membrane-feeding assay (SMFA) has been used as a "gold standard" assay for TBV ...development. However, in SMFA, the inhibitory activity is commonly measured at oocyst stage of parasites, while it is the sporozoites which transmit malaria from a mosquito to a human. A handful of studies have shown that there is a positive correlation between oocyst and sporozoite intensities. However, no study has been completed to compare inhibition levels in oocyst and sporozoite intensities in the presence of transmission-blocking (TB) antibodies.
Plasmodium falciparum NF54 gametocytes were fed to Anopheles stephensi mosquitoes with or without anti-Pfs25 or anti-Pfs48/45 TB antibodies in 15 independent assays. For each group, a portion of the mosquitoes was dissected for oocyst counts (day 8 after feed), and a portion of the remaining mosquitoes was dissected for sporozoite counts (day 16). This study covered a large range of oocyst and sporozoite intensities: 0.2 to 80.5 on average for oocysts, and 141 to 77,417 for sporozoites. The sporozoite data were well explained by a zero-inflated negative binomial model, regardless of the presence or absence of TB antibodies. Inhibition levels in both oocyst and sporozoite intensities were determined within the same groups in 9 independent assays. When the level of inhibition in sporozoite number (expressed as Log Mean Ratio, LMR; average number in a control group was divided by the one in a test group, then took a log of the ratio) was plotted against LMR in oocyst number, the best-fit slope of a linear regression was not different from 1 (the best estimate, 1.08; 95% confidence interval, 0.87 to 1.29). Furthermore, a Bland-Altman analysis showed a strong agreement between inhibitions in oocysts and in sporozoites.
The results indicate that percent inhibition in oocyst intensity of a test sample can be directly converted to % inhibition in sporozoite intensity in P. falciparum SMFA. Therefore, if sporozoite intensity determines transmission rate from mosquitoes to humans, the percent inhibition in oocyst intensity measured by SMFA can be used to estimate the TBV efficacy.
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