While cell migration can be directed by various mechanical cues such as force, deformation, stiffness, or flow, the associated mechanisms and functions may remain elusive. Single cell migration against flow, repeatedly reported with leukocytes, is arguably considered as active and mediated by integrin mechanotransduction, or passive and determined by a mechanical bias. Here, we reveal a phenotype of flow mechanotaxis with fish epithelial keratocytes that orient upstream or downstream at shear stresses around tens of dyn cm −2 . We show that each cell has an intrinsic orientation that results from the mechanical interaction of flow with its morphology. The bulbous trailing edge of a keratocyte generates a hydrodynamical torque under flow that stabilizes an upstream orientation, just as the heavy lower edge of a roly-poly toy generates a gravitational torque that stabilizes an upright position. In turn, the wide and flat leading edge of keratocytes destabilizes upstream orientation, allowing the existence of two distinct phenotypes. To formalize these observations, we propose a simple mechanical model that considers keratocyte morphology as a hemisphere preceded by a wide thin sheet. Our findings show that this model can recapitulate the phase diagram of single cell orientation under flow without adjustable parameters. From a larger perspective, this passive mechanism of keratocytes flow mechanotaxis implies a potential absence of physiological function and evolution-driven process.

中文翻译：

---

角膜形成细胞以类似 roly-poly 的机制逆流迁移

虽然细胞迁移可以通过各种机械线索（如力、变形、刚度或流动）来指导，但相关的机制和功能可能仍然难以捉摸。单细胞逆流迁移，反复报道白细胞，可以说是主动的，由整合素机械转导介导，或被动的，由机械偏差决定。在这里，我们揭示了鱼类上皮角质形成细胞的流动趋机械性表型，该表型在大约数十达因厘米的剪切应力下向上游或下游−2. 我们表明每个细胞都有一个内在的方向，这是由流动与其形态的机械相互作用引起的。角质形成细胞的球根状后缘在流动下产生流体动力扭矩，稳定上游方向，就像不倒翁玩具的沉重下边缘产生重力扭矩，稳定直立位置。反过来，角膜细胞宽而扁平的前缘破坏了上游方向的稳定性，从而允许存在两种不同的表型。为了使这些观察结果形式化，我们提出了一个简单的机械模型，该模型将角质形成细胞形态视为一个半球，前面是一个宽薄的薄片。我们的研究结果表明，该模型可以在没有可调参数的情况下重现单细胞定向相图。从更大的角度来看，