Guevorkian Karine, Manzi John, Pontani Léa-Lætitia, Brochard-Wyart Françoise, Sykes Cécile
Laboratoire Physico Chimie Curie, Institut Curie, PSL Research University, CNRS UMR168, Paris, France; Sorbonne Universités, UPMC Univ Paris 06, Paris, France; Institut de Génétique et de Biologie Moléculaire et Cellulaire, Université de Strasbourg, Centre National de la Recherche Scientifique, UMR 7104, Institut National de la Santé et de la Recherche Médicale, U964, Illkirch, France.
Laboratoire Physico Chimie Curie, Institut Curie, PSL Research University, CNRS UMR168, Paris, France; Sorbonne Universités, UPMC Univ Paris 06, Paris, France.
Biophys J. 2015 Dec 15;109(12):2471-2479. doi: 10.1016/j.bpj.2015.10.050.
Cell-shape changes are insured by a thin, dynamic, cortical layer of cytoskeleton underneath the plasma membrane. How this thin cortical structure impacts the mechanical properties of the whole cell is not fully understood. Here, we study the mechanics of liposomes or giant unilamellar vesicles, when a biomimetic actin cortex is grown at the inner layer of the lipid membrane via actin-nucleation-promoting factors. Using a hydrodynamic tube-pulling technique, we show that tube dynamics is clearly affected by the presence of an actin shell anchored to the lipid bilayer. The same force pulls much shorter tubes in the presence of the actin shell compared to bare membranes. However, in both cases, we observe that the dynamics of tube extrusion has two distinct features characteristic of viscoelastic materials: rapid elastic elongation, followed by a slower elongation phase at a constant rate. We interpret the initial elastic regime by an increase of membrane tension due to the loss of lipids into the tube. Tube length is considerably shorter for cortex liposomes at comparable pulling forces, resulting in a higher spring constant. The presence of the actin shell seems to restrict lipid mobility, as is observed in the corral effect in cells. The viscous regime for bare liposomes corresponds to a leakout of the internal liquid at constant membrane tension. The presence of the actin shell leads to a larger friction coefficient. As the tube is pulled from a patchy surface, membrane tension increases locally, leading to a Marangoni flow of lipids. As a conclusion, the presence of an actin shell is revealed by its action that alters membrane mechanics.
细胞形状的改变由质膜下方一层薄的、动态的细胞骨架皮质层所保障。然而，这种薄的皮质结构如何影响整个细胞的力学性质尚未完全明确。在这里，我们研究了脂质体或巨型单层囊泡的力学性质，即在通过肌动蛋白成核促进因子在脂质膜内层生长仿生肌动蛋白皮质层的情况下。使用流体动力学管拉伸技术，我们发现管的动力学明显受到锚定在脂质双层上的肌动蛋白壳层的影响。与裸露的膜相比，在有肌动蛋白壳层存在时，相同的力拉动的管要短得多。然而，在这两种情况下，我们观察到管挤出的动力学具有粘弹性材料的两个不同特征：快速的弹性伸长，随后是以恒定速率的较慢伸长阶段。我们将初始弹性阶段解释为由于脂质进入管中导致膜张力增加。在可比的拉力下，皮质脂质体的管长度明显更短，从而导致更高的弹簧常数。肌动蛋白壳层的存在似乎限制了脂质的流动性，这在细胞的围栏效应中也有观察到。裸露脂质体的粘性阶段对应于在恒定膜张力下内部液体的泄漏。肌动蛋白壳层的存在导致更大的摩擦系数。当管从斑驳表面被拉动时，膜张力局部增加，导致脂质的马兰戈尼流。总之，肌动蛋白壳层的存在通过其改变膜力学的作用得以揭示。
