Going with the Flow (or Not).
Going with the Flow (or Not).
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随波逐流（或不随波逐流）。
DOI：
10.1016/j.bpj.2019.07.049
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发表时间：
2019
影响因子：
3.4
通讯作者：
Kapustina,Maryna
中科院分区：
文献类型：
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作者：
Jacobson,Ken;Kapustina,Maryna
膜流动的问题已经在膜生物学家和生物药理学家的脑海中几十年了，从1971年观察到补丁抗原的封盖开始（1）。解释这一现象的一个假设是，质膜中的脂质向后流动，由细胞前部的胞吐作用和细胞后部的胞吞作用驱动（2）。这种从前到后的脂质流动被认为是为了清扫大的、缓慢扩散的抗原斑块，并将它们带到细胞的后部，形成一个帽。虽然表面上很吸引人，但后来观察到补丁抗原与逆行流动的皮质细胞骨架一致移动，这一假设被削弱了（3）。此外，在许多现象中，包括细胞迁移（4），形态振荡（5），胚胎形态发生（6）和吞噬作用（7），储存在表面褶皱中的膜可以展开，以提供覆盖细胞延伸所需的表面积，这表明了一种中尺度的整体表面运输。然而，逆行流动假说并没有被排除。最近，奥尼尔等人。(8)表明逆行膜流是游泳细胞运动所必需的，尽管问题仍然是脂双层是否真的在流动。令人惊讶的是，通过从扩散细胞的质膜的背侧表面拉动邻近的系链，Shi et al. (9)发现膜张力变化不会传播超过5微米量级的距离，而这种限制在膜泡中不存在。这些观察结果表明，在这样的距离之外，质膜中缺乏脂质流动。在科学上，通过完全独立的方法证实意外发现的能力总是值得称赞的。使用两点微观流变学方法，Chein等人在这一期的《生物物理学杂志》（10）中报道了由于在彼此不同距离处计算的相同类型的两个个体受体之间的扩散而引起的位移的相关性。将TrkB或p75跨膜受体转染到人胚肾细胞或培养的神经元中，并使用酰基载体蛋白-CoA系统进行外部标记，其中荧光缀合的CoA结合到与小（10 kDa）酰基载体蛋白融合的受体。使用全内反射显微镜在腹侧细胞表面上进行单分子追踪。结果表明，流体动力学耦合位移的一个接收器到一个接近的一个是强大的流场在0.45微米，但不延伸超过1.5微米。作者还证实，这一结果不依赖于所研究的受体或细胞类型。理论上的期望是，
The issue of membrane flow has been on the minds of membrane biologists and biophysicists for decades, beginning with the observation of the capping of patched antigens in 1971 (1). One hypothesis to explain this phenomenon was that the lipids in the plasma membrane flowed rearward, driven by exocytosis at the front of the cell and endocytosis at the rear of the cell (2). This front-to-rear lipid flow was postulated to sweep up large, slowly diffusing patches of antigen and carry them to rear of the cell, forming a cap. Although superficially attractive, this hypothesis was later weakened by the observation that patched antigens move in concert with a retrograde flowing cortical cytoskeleton (3). Moreover, in a number of phenomena—including cell migration (4), morphological oscillations (5), embryonic morphogenesis (6), and phagocytosis (7)—membrane stored in surface folds can be unfolded to provide the surface area required to cover cell extensions, indicating a type of bulk surface transport on the mesoscale. Yet the retrograde flow hypothesis has not been ruled out. Recently, O’Neill et al.(8) showed that retrograde membrane flow was required for the locomotion of swimming cells, although the question remains whether the lipid bilayer is actually flowing. Surprisingly, by pulling proximate tethers from the dorsal surface of plasma membrane of spread cells, Shi et al.(9) found that membrane tension changes do not propagate further than distances on the order of 5 microns, whereas such limitations do not exist in membrane blebs. These observations indicated a lack of lipid flow in the plasma membrane beyond such distances.In science, the ability to corroborate unexpected findings by completely independent methods is always to be applauded. Using two-point microrheological methodology, Chein et al. in this issue of Biophysical Journal (10) report the correlations in the displacements due to diffusion between two individual receptors of the same type calculated at various distances from each other. TrkB or p75 transmembrane receptors were transfected into human embryonic kidney cells or cultured neurons and labeled externally using the acyl carrier protein-CoA system, in which the fluorescentconjugated CoA binds to a receptor fused to a small (10 kDa) acyl carrier protein. Single-molecule tracking was done using total internal reflection microscopy on the ventral cell surface. The results show that the flow field that hydrodynamically couples displacement of one receptor to a proximate one is strong within 0.45 microns but does not extend past 1.5 microns. The authors also confirm that this result does not depend on the receptor or cell type studied. The theoretical expectation is that the flow fields within the