Root elongation and bending require the coordinated expansion of multiple cells of different types. These processes are regulated by the action of hormones that can target distinct cell layers. We ...use a mathematical model to characterise the influence of the biomechanical properties of individual cell walls on the properties of the whole tissue. Taking a simple constitutive model at the cell scale which characterises cell walls via yield and extensibility parameters, we derive the analogous tissue‐level model to describe elongation and bending. To accurately parameterise the model, we take detailed measurements of cell turgor, cell geometries and wall thicknesses. The model demonstrates how cell properties and shapes contribute to tissue‐level extensibility and yield. Exploiting the highly organised structure of the elongation zone (EZ) of the Arabidopsis root, we quantify the contributions of different cell layers, using the measured parameters. We show how distributions of material and geometric properties across the root cross‐section contribute to the generation of curvature, and relate the angle of a gravitropic bend to the magnitude and duration of asymmetric wall softening. We quantify the geometric factors which lead to the predominant contribution of the outer cell files in driving root elongation and bending.
Ion pairing between the major phospholipids of the Staphylococcus aureus plasma membrane (phosphatidylglycerol – PG and lysyl‐phosphatidylglycerol – LPG) confers resistance to antimicrobial peptides ...and other antibiotics. We developed 3adLPG, a stable synthetic analogue which can substitute for the highy‐labile native LPG, in biophysical experiments examining the membrane‐protecting role of lipid ion pairing, in S. aureus and other important bacteria. Here we examine the surface charge and lipid packing characteristics of synthetic biomimetic mixtures of DPPG and DP3adLPG in Langmuir monolayers, using a combination of complementary surface‐probing techniques such as infrared reflection‐absorption spectroscopy and grazing‐incidence x‐ray diffraction. The resultant phase diagram for the ion paired lipids sheds light on the mixing behavior of lipids in monolayer models of resistant phenotype bacterial membranes, and provides a platform for future biophysical studies.
Lipid ion pairing in antibiotic‐resistant bacteria: A biomimetic binary mixed monolayer is used to model the effect of ion pairing between synthetic Staphylococcus aureus phospholipids on lipid packing and interfacial charge. The resultant phase diagram aids our understanding of how membrane composition plasticity may tune the bilayer physicochemical properties in response to antibiotic stress.
The basement membrane (BM) is a thin layer of extracellular matrix (ECM) beneath nearly all epithelial cell types that is critical for cellular and tissue function. It is composed of numerous ...components conserved among all bilaterians 1; however, it is unknown how all of these components are generated and subsequently constructed to form a fully mature BM in the living animal. Although BM formation is thought to simply involve a process of self-assembly 2, this concept suffers from a number of logistical issues when considering its construction in vivo. First, incorporation of BM components appears to be hierarchical 3–5, yet it is unclear whether their production during embryogenesis must also be regulated in a temporal fashion. Second, many BM proteins are produced not only by the cells residing on the BM but also by surrounding cell types 6–9, and it is unclear how large, possibly insoluble protein complexes 10 are delivered into the matrix. Here we exploit our ability to live image and genetically dissect de novo BM formation during Drosophila development. This reveals that there is a temporal hierarchy of BM protein production that is essential for proper component incorporation. Furthermore, we show that BM components require secretion by migrating macrophages (hemocytes) during their developmental dispersal, which is critical for embryogenesis. Indeed, hemocyte migration is essential to deliver a subset of ECM components evenly throughout the embryo. This reveals that de novo BM construction requires a combination of both production and distribution logistics allowing for the timely delivery of core components.
•Macrophages are major producers of basement membrane in the Drosophila embryo•Basement membrane components require hierarchical deposition during development•Macrophage migration is essential to evenly deliver a subset of matrix components•Uneven macrophage dispersal leads to uneven matrix incorporation and lethality
Drosophila macrophages undergo stereotyped developmental migrations to evenly populate the embryo. Matsubayashi et al. reveal that macrophages are the biggest producers of extracellular matrix in the embryo and that their dispersal is essential to evenly distribute a subset of matrix components during development.
Activation of the nuclear factor erythroid 2–related factor 2 (Nrf2) pathway is critical for vascular endothelial redox homeostasis in regions of high, unidirectional shear stress (USS), however the ...underlying mechanosensitive mediators are not fully understood. The endothelial glycocalyx is disrupted in arterial areas exposed to disturbed blood flow that also exhibit enhanced oxidative stress leading to atherogenesis. We investigated the contribution of glycocalyx sialic acids (SIA) to Nrf2 signaling in human endothelial cells (EC) exposed to atheroprotective USS or atherogenic low oscillatory shear stress (OSS). Cells exposed to USS exhibited a thicker glycocalyx and enhanced turnover of SIA which was reduced in cells cultured under OSS. Physiological USS, but not disturbed OSS, enhanced Nrf2-mediated expression of antioxidant enzymes, which was attenuated following SIA cleavage with exogenous neuraminidase. SIA removal disrupted kinase signaling involved in the nuclear accumulation of Nrf2 elicited by USS and promoted mitochondrial reactive oxygen species accumulation. Notably, knockdown of the endogenous sialidase NEU1 potentiated Nrf2 target gene expression, directly implicating SIA in regulation of Nrf2 signaling by USS. In the absence of SIA, deficits in Nrf2 responses to physiological flow were also associated with a pro-inflammatory EC phenotype. This study demonstrates that the glycocalyx modulates endothelial redox state in response to shear stress and provides the first evidence of an atheroprotective synergism between SIA and Nrf2 antioxidant signaling. The endothelial glycocalyx therefore represents a potential therapeutic target against EC dysfunction in cardiovascular disease and redox dyshomeostasis in ageing.
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•Oscillatory but not laminar shear stress reduces endothelial glycocalyx sialic acid.•Laminar shear stress activates Nrf2-regulated endogenous antioxidant defences.•Disruption of sialic acids attenuates Nrf2 activation by laminar shear stress.•Knockdown of endogenous sialidase NEU1 enhances Nrf2 responses to flow.•The glycocalyx maintains endothelial redox homeostasis in response to shear stress.
Senescence is a cellular phenotype present in health and disease, characterized by a stable cell-cycle arrest and an inflammatory response called senescence-associated secretory phenotype (SASP). The ...SASP is important in influencing the behavior of neighboring cells and altering the microenvironment; yet, this role has been mainly attributed to soluble factors. Here, we show that both the soluble factors and small extracellular vesicles (sEVs) are capable of transmitting paracrine senescence to nearby cells. Analysis of individual cells internalizing sEVs, using a Cre-reporter system, show a positive correlation between sEV uptake and senescence activation. We find an increase in the number of multivesicular bodies during senescence in vivo. sEV protein characterization by mass spectrometry (MS) followed by a functional siRNA screen identify interferon-induced transmembrane protein 3 (IFITM3) as being partially responsible for transmitting senescence to normal cells. We find that sEVs contribute to paracrine senescence.
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•Small extracellular vesicles (sEVs) mediate paracrine senescence•Inhibition of sEV biogenesis prevents paracrine senescence•Multivesicular bodies and CD63 are increased during senescence in vivo•MS analysis identifies IFITM3 as partially responsible for sEV-paracrine senescence
Borghesan et al. show that the soluble fraction and small extracellular vesicles (sEVs) mediate paracrine senescence. RNA sequencing and loxP reporter systems confirm sEV-mediated paracrine senescence, while preventing sEV release averts senescence. Mass spectrometry and functional analysis show that the IFN protein, IFITM3, is partially responsible for this phenotype.
Mitochondria and the endoplasmic reticulum (ER) form tight structural associations and these facilitate a number of cellular functions. However, the mechanisms by which regions of the ER become ...tethered to mitochondria are not properly known. Understanding these mechanisms is not just important for comprehending fundamental physiological processes but also for understanding pathogenic processes in some disease states. In particular, disruption to ER-mitochondria associations is linked to some neurodegenerative diseases. Here we show that the ER-resident protein VAPB interacts with the mitochondrial protein tyrosine phosphatase-interacting protein-51 (PTPIP51) to regulate ER-mitochondria associations. Moreover, we demonstrate that TDP-43, a protein pathologically linked to amyotrophic lateral sclerosis and fronto-temporal dementia perturbs ER-mitochondria interactions and that this is associated with disruption to the VAPB-PTPIP51 interaction and cellular Ca(2+) homeostasis. Finally, we show that overexpression of TDP-43 leads to activation of glycogen synthase kinase-3β (GSK-3β) and that GSK-3β regulates the VAPB-PTPIP51 interaction. Our results describe a new pathogenic mechanism for TDP-43.
The Arabidopsis thaliana MYB26/MALE STERILE35 (MS35) gene is critical for the development of secondary thickening in the anther endothecium and subsequent dehiscence. MYB26 is localized to the ...nucleus and regulates endothecial development and secondary thickening in a cell-specific manner in the anther. MYB26 expression is seen in anthers and also in the style and nectaries, although there is no effect on female fertility in the ms35 mutant. MYB26 expression in anthers occurs early during endothecial development, with maximal expression during pollen mitosis I and bicellular stages, indicating a regulatory role in specifying early endothecial cell development. Overexpression of MYB26 results in ectopic secondary thickening in both Arabidopsis and tobacco (Nicotiana tabacum) plants, predominantly within the epidermal tissues. MYB26 regulates a number of genes linked to secondary thickening, including IRREGULAR XYLEM1 (IRX1), IRX3, IRX8, and IRX12. Changes in expression were also detected in two NAC domain genes, NAC SECONDARY WALL-PROMOTING FACTOR1 (NST1) and NST2, which have been linked to secondary thickening in the anther endothecium. These data indicate that MYB26 regulates NST1 and NST2 expression and in turn controls the process of secondary thickening. Therefore, MYB26 appears to function in a regulatory role involved in determining endothecial cell development within the anther and acts upstream of the lignin biosynthesis pathway.
Sustained activation of X-box-binding protein 1 (XBP1) results in endothelial cell (EC) apoptosis and atherosclerosis development. The present study provides evidence that XBP1 mRNA splicing ...triggered an autophagic response in ECs by inducing autophagic vesicle formation and markers of autophagy BECLIN-1 and microtubule-associated protein 1 light chain 3β (LC3-βII). Endostatin activated autophagic gene expression through XBP1 mRNA splicing in an inositol-requiring enzyme 1α (IRE1α)-dependent manner. Knockdown of XBP1 or IRE1α by shRNA in ECs ablated endostatin-induced autophagosome formation. Importantly, data from arterial vessels from XBP1 EC conditional knock-out (XBP1eko) mice demonstrated that XBP1 deficiency in ECs reduced the basal level of LC3β expression and ablated response to endostatin. Chromatin immunoprecipitation assays further revealed that the spliced XBP1 isoform bound directly to the BECLIN-1 promoter at the region from nt −537 to −755. BECLIN-1 deficiency in ECs abolished the XBP1-induced autophagy response, whereas spliced XBP1 did not induce transcriptional activation of a truncated BECLIN-1 promoter. These results suggest that XBP1 mRNA splicing triggers an autophagic signal pathway through transcriptional regulation of BECLIN-1.
Background: Apoptosis and autophagy are two closely related systems that induce cell death.
Results: X-box-binding protein 1 (XBP1) mRNA splicing regulates BECLIN-1 transcriptional activation, a fundamental player in the initiation of autophagy.
Conclusion:XBP1 splicing induces an autophagic response in endothelial cells.
Significance: XBP1 could be used as an important pharmacological target that can regulate the autophagic machinery and endothelial cell death.
The Arabidopsis thaliana MALE STERILITY1 (MS1) gene is critical for viable pollen formation and has homology to the PHD-finger class of transcription factors; however, its role in pollen development ...has not been fully defined. We show that MS1 transcription appears to be autoregulated by the wild-type MS1 transcript or protein. Using a functional green fluorescent protein (GFP) fusion to analyze the temporal and spatial expression of MS1, we demonstrate that the MS1:GFP protein is nuclear localized within the tapetum and is expressed in a developmentally regulated manner between late tetraspore and microspore release, then rapidly breaks down, probably by ubiquitin-dependent proteolysis. Absence of MS1 expression results in changes in tapetal secretion and exine structure. Microarray analysis has shown that 260 (228 downregulated and 32 upreglated) genes have altered expression in young ms1 buds. These genes are primarily associated with pollen wall and coat formation; however, a number of transcription factors and Cys proteases have also been identified as the putative primary regulatory targets of MS1. Ectopic expression of MS1 alters transcriptional regulation of vegetative gene expression, resulting in stunted plants with increased levels of branching, partially fertile flowers and an apparent increase in wall material on mature pollen. MS1 therefore plays a critical role in the induction of pollen wall and pollen coat materials in the tapetum and, ultimately, the production of viable pollen.
WBP2 encodes the WW domain‐binding protein 2 that acts as a transcriptional coactivator for estrogen receptor α (ESR1) and progesterone receptor (PGR). We reported that the loss of Wbp2 expression ...leads to progressive high‐frequency hearing loss in mouse, as well as in two deaf children, each carrying two different variants in the WBP2 gene. The earliest abnormality we detect in Wbp2‐deficient mice is a primary defect at inner hair cell afferent synapses. This study defines a new gene involved in the molecular pathway linking hearing impairment to hormonal signalling and provides new therapeutic targets.
Synopsis
WBP2 was found to underlie deafness in mouse and patients. Wbp2‐deficient mice were used as a genetic tool to gain insight into the functional link between hormonal signalling and hearing impairment.
WBP2 mutations lead to deafness in mouse and humans.
In the Wbp2‐mutant mouse, the earliest abnormality is swelling of afferent nerve endings below inner hair cells and mice show progressive high‐frequency hearing loss.
Wbp2 deficiency leads to reduced expression of estrogen and progesterone receptors in the cochlea and disrupted expression of key post‐synaptic proteins.
WBP2 was found to underlie deafness in mouse and patients. Wbp2‐deficient mice were used as a genetic tool to gain insight into the functional link between hormonal signalling and hearing impairment.
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