scholarly journals A Rationale for Mesoscopic Domain Formation in Biomembranes

Biomolecules ◽  
2018 ◽  
Vol 8 (4) ◽  
pp. 104 ◽  
Author(s):  
Nicolas Destainville ◽  
Manoel Manghi ◽  
Julie Cornet
Keyword(s):  
Symmetry Breaking ◽  
Plasma Membranes ◽  
Condensed Matter ◽  
Structural Complexity ◽  
Protein Composition ◽  
Lipid Vesicles ◽  
Model Systems ◽  
Condensed Matter Physics ◽  
Experimental Conditions

Cell plasma membranes display a dramatically rich structural complexity characterized by functional sub-wavelength domains with specific lipid and protein composition. Under favorable experimental conditions, patterned morphologies can also be observed in vitro on model systems such as supported membranes or lipid vesicles. Lipid mixtures separating in liquid-ordered and liquid-disordered phases below a demixing temperature play a pivotal role in this context. Protein-protein and protein-lipid interactions also contribute to membrane shaping by promoting small domains or clusters. Such phase separations displaying characteristic length-scales falling in-between the nanoscopic, molecular scale on the one hand and the macroscopic scale on the other hand, are named mesophases in soft condensed matter physics. In this review, we propose a classification of the diverse mechanisms leading to mesophase separation in biomembranes. We distinguish between mechanisms relying upon equilibrium thermodynamics and those involving out-of-equilibrium mechanisms, notably active membrane recycling. In equilibrium, we especially focus on the many mechanisms that dwell on an up-down symmetry breaking between the upper and lower bilayer leaflets. Symmetry breaking is an ubiquitous mechanism in condensed matter physics at the heart of several important phenomena. In the present case, it can be either spontaneous (domain buckling) or explicit, i.e., due to an external cause (global or local vesicle bending properties). Whenever possible, theoretical predictions and simulation results are confronted to experiments on model systems or living cells, which enables us to identify the most realistic mechanisms from a biological perspective.

scholarly journals A rationale for mesoscopic domain formation in biomembranes

2018 ◽  
Author(s):  
Nicolas Destainville ◽  
Manoel Manghi ◽  
Julie Cornet
Keyword(s):  
Symmetry Breaking ◽  
Plasma Membranes ◽  
Condensed Matter ◽  
Structural Complexity ◽  
Protein Composition ◽  
Lipid Vesicles ◽  
Model Systems ◽  
Condensed Matter Physics ◽  
Experimental Conditions

Cell plasma membranes display a dramatically rich structural complexity characterized by functional sub-wavelength domains with specific lipid and protein composition. Under favorable experimental conditions, patterned morphologies can also be observed in vitro on model systems such as supported membranes or lipid vesicles. Lipid mixtures separating in liquid-ordered and liquid-disordered phases below a demixing temperature play a pivotal role in this context. Protein-protein and protein-lipid interactions also contribute to membrane shaping by promoting small domains or clusters. Such phase separations displaying characteristic length-scales falling in-between the nanoscopic, molecular scale on the one hand and the macroscopic scale on the other hand, are named mesophases in soft condensed matter physics. In this Review, we propose a classification of the diverse mechanisms leading to mesophase separation in biomembranes. We distinguish between mechanisms relying upon equilibrium thermodynamics and those involving out-of-equilibrium mechanisms, notably active membrane recycling. In equilibrium, we show that the mechanisms generically dwell on an up-down symmetry breaking between the upper and lower bilayer leaflets. Symmetry breaking is an ubiquitous mechanism in condensed matter physics at the heart of several important phenomena. In the present case, it can be either spontaneous (domain buckling) or explicit, i.e. due to an external cause (global or local vesicle bending properties). Whenever possible, theoretical predictions and simulation results are confronted to experiments on model systems or living cells, which enables us to identify the most realistic mechanisms from a biological perspective.

Observations of Frozen-Hydrated Microtubules

1990 ◽  
Vol 48 (1) ◽  
pp. 504-505
Author(s):  
D. Chrétien ◽  
D. Job ◽  
R.H. Wade
Keyword(s):  
Fourier Transforms ◽  
Structural Complexity ◽  
Image Contrast ◽  
Phase Behaviour ◽  
Experimental Conditions ◽  
Thin Sections ◽  
Surface Lattice ◽  
Cilia And Flagella ◽  
Outstanding Question

Microtubules are filamentary structures found in the cytoplasm of eukaryotic cells, where, together with actin and intermediate filaments, they form the components of the cytoskeleton. They have many functions and show various levels of structural complexity as witnessed by the singlet, doublet and triplet structures involved in the architecture of centrioles, basal bodies, cilia and flagella. The accepted microtubule model consists of a 25 nm diameter hollow tube with a wall made up of 13 paraxial protofilaments (pf). Each pf is a string of aligned tubulin dimers. Some results have suggested that the pfs follow a superhelix. To understand how microtubules function in the cell an accurate model of the surface lattice is one of the requirements. For example the 9x2 architecture of the axoneme will depend on the organisation of its component microtubules. We should also note that microtubules with different numbers of pfs have been observed in thin sections of cellular and of in-vitro material. An outstanding question is how does the surface lattice adjust to these different pf numbers?We have been using cryo-electron microscopy of frozen-hydrated samples to study in-vitro assembled microtubules. The experimental conditions are described in detail in this reference. The results obtained in conjunction with thin sections of similar specimens and with axoneme outer doublet fragments have already allowed us to characterise the image contrast of 13, 14 and 15 pf microtubules on the basis of the measured image widths, of the the image contrast symmetry and of the amplitude and phase behaviour along the equator in the computed Fourier transforms. The contrast variations along individual microtubule images can be interpreted in terms of the geometry of the microtubule surface lattice. We can extend these results and make some reasonable predictions about the probable surface lattices in the case of other pf numbers, see Table 1. Figure 1 shows observed images with which these predictions can be compared.

scholarly journals Angiotensin II inhibits NaCl absorption in the rat medullary thick ascending limb

2004 ◽  
Vol 287 (3) ◽  
pp. F404-F410 ◽  
Author(s):  
Nicolas Lerolle ◽  
Soline Bourgeois ◽  
Françoise Leviel ◽  
Gaëtan Lebrun ◽  
Michel Paillard ◽  
...  
Keyword(s):  
Angiotensin Ii ◽  
Plasma Membranes ◽  
Inhibitory Effect ◽  
Thick Ascending Limb ◽  
Sprague Dawley ◽  
Experimental Conditions ◽  
Nacl Absorption ◽  
Medullary Thick Ascending Limb

NaCl reabsorption in the medullary thick ascending limb of Henle (MTALH) contributes to NaCl balance and is also responsible for the creation of medullary interstitial hypertonicity. Despite the presence of angiotensin II subtype 1 (AT1) receptors in both the luminal and the basolateral plasma membranes of MTALH cells, no information is available on the effect of angiotensin II on NaCl reabsorption in MTALH and, furthermore, on angiotensin II-dependent medullary interstitial osmolality. MTALHs from male Sprague-Dawley rats were isolated and microperfused in vitro; transepithelial net chloride absorption ( JCl) as well as transepithelial voltage ( Vte) were measured. Luminal or peritubular 10−11 and 10−10 M angiotensin II had no effect on JCl or Vte. However, 10−8 M luminal or peritubular angiotensin II reversibly decreased both JCl and Vte. The effect of both luminal and peritubular angiotensin II was prevented by the presence of losartan (10−6 M). By contrast, PD-23319, an AT2-receptor antagonist, did not alter the inhibitory effect of 10−8 M angiotensin II. Finally, no additive effect of luminal and peritubular angiotensin II was observed. We conclude that both luminal and peritubular angiotensin II inhibit NaCl absorption in the MTALH via AT1 receptors. Because of intrarenal angiotensin II synthesis, angiotensin II concentration in medullary tubular and interstitial fluids may be similar in vivo to the concentration that displays an inhibitory effect on NaCl reabsorption under the present experimental conditions.

FROM BCS TO THE LHC

2008 ◽  
Vol 23 (11) ◽  
pp. 1627-1635 ◽  
Author(s):  
STEVEN WEINBERG
Keyword(s):  
Symmetry Breaking ◽  
Spontaneous Symmetry Breaking ◽  
Particle Physics ◽  
Condensed Matter ◽  
50Th Anniversary ◽  
Condensed Matter Physics ◽  
University Of Illinois ◽  
The University ◽  
Theory Of Superconductivity

Reflections on spontaneous symmetry breaking, and the connection between condensed matter physics and particle physics, as given in a talk at a symposium at the University of Illinois in Urbana, celebrating the 50th anniversary of the theory of superconductivity.

Biological Responses of Fibroblasts to Cyclic Stretching: A Novel Culture Model Study

2000 ◽  
Author(s):  
James H.-C. Wang ◽  
David Stone ◽  
Fengyan Jia ◽  
Chris Celechovsky ◽  
Savio L.-Y. Woo
Keyword(s):  
Control Cell ◽  
Model Systems ◽  
Cell Alignment ◽  
Experimental Conditions ◽  
Cyclic Stretching ◽  
Biological Responses ◽  
Model Study ◽  
Vitro Model

Abstract Because of the advantage of better control of experimental conditions, in vitro model systems have been developed to examine the effects of mechanical loading on cells. Previous studies have shown that cyclic stretching causes cells to change orientation, proliferation and gene expression (Buck et al., 1980; Wang et al., 1995; Leung et al., 1976). However, one drawback of these model systems is that they are unable to control cell alignment and shape, and in addition, some provide heterogeneous strains to cells during stretching (See review by Schaffer, 1994). Consequently, cellular responses in these systems may not be similar to those in vivo. For example, tendon and ligament fibroblasts align with collagen fibers in vivo and are hence subjected to stretching along the tissue long axis. In contrast, in many existing systems, cells either randomly orient or orient away from the stretching direction.

In vitro effect of free bile acids on the bile canaliular membrane phospholipids in the rat

1976 ◽  
Vol 54 (12) ◽  
pp. 1040-1046 ◽  
Author(s):  
I. M. Yousef ◽  
M. M. Fisher
Keyword(s):  
Bile Acid ◽  
Plasma Membranes ◽  
Membrane Phospholipid ◽  
Male Rats ◽  
Membrane Phospholipids ◽  
Experimental Conditions ◽  
Cell Plasma ◽  
Vitro Effect ◽  
Free Bile Acids

Liver cell plasma membranes of male rats were isolated and separated into two fractions, one rich in bile canalicular membranes (BCM) and the other comprising the rest of the plasma membranes (PM). Aliquots of BCM, PM, and microsomes were incubated with deoxycholic, chenodeoxycholic, or cholic acid at bile acid – membrane phospholipid mole ratios up to 100, and the phospholipids solubilized from the membranes were analyzed.Phospholipid solubilization from the PM and from microsomes was linear and apparently nonselective, while that from the BCM was biphasic and distinctly selective. Phosphatidyl choline and phosphatidyl ethanolamine made up 90% of the phospholipids solubilized from the BCM at a bile acid – membrane phospholipid mole ratio sufficient to solubilize about 50% of the total phospholipids of the BCM. Of particular interest was the observation that the molecular species and fatty acid composition of the phospholipids solubilized from the BCM under these experimental conditions were similar to those of bile obtained from the same animal, and were quite unlike those solubilized at higher bile acid – phospholipid mole ratios. The data are discussed in terms of the mechanism of the biliary secretion of phospholipids.

scholarly journals Symmetry breaking and the deconstruction of mass

2015 ◽  
Vol 373 (2032) ◽  
pp. 20140034 ◽  
Author(s):  
Luis Álvarez-Gaumé
Keyword(s):  
Symmetry Breaking ◽  
Particle Physics ◽  
Condensed Matter ◽  
Current Understanding ◽  
Condensed Matter Physics

We briefly review some of the connections between symmetry breaking in condensed matter physics and in particle physics, assisting, in particular, our current understanding of the origin of mass.

scholarly journals Symmetry breaking in reconstituted actin cortices

eLife ◽  
2014 ◽  
Vol 3 ◽  
Author(s):  
Enas Abu Shah ◽  
Kinneret Keren
Keyword(s):  
Symmetry Breaking ◽  
Break Symmetry ◽  
Model Systems ◽  
Cortical Actin ◽  
Artificial System ◽  
Actin Cortex ◽  
The Rich ◽  
Oil Emulsions

The actin cortex plays a pivotal role in cell division, in generating and maintaining cell polarity and in motility. In all these contexts, the cortical network has to break symmetry to generate polar cytoskeletal dynamics. Despite extensive research, the mechanisms responsible for regulating cortical dynamics in vivo and inducing symmetry breaking are still unclear. Here we introduce a reconstituted system that self-organizes into dynamic actin cortices at the inner interface of water-in-oil emulsions. This artificial system undergoes spontaneous symmetry breaking, driven by myosin-induced cortical actin flows, which appears remarkably similar to the initial polarization of the embryo in many species. Our in vitro model system recapitulates the rich dynamics of actin cortices in vivo, revealing the basic biophysical and biochemical requirements for cortex formation and symmetry breaking. Moreover, this synthetic system paves the way for further exploration of artificial cells towards the realization of minimal model systems that can move and divide.

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