Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA.
Computer Science Department, Brandeis University, Waltham, MA 02453, USA.
Curr Biol. 2022 Sep 12;32(17):3745-3757.e7. doi: 10.1016/j.cub.2022.07.034. Epub 2022 Aug 12.
Cells are complex biochemical systems whose behaviors emerge from interactions among myriad molecular components. Computation is often invoked as a general framework for navigating this cellular complexity. However, it is unclear how cells might embody computational processes such that the theories of computation, including finite-state machine models, could be productively applied. Here, we demonstrate finite-state-machine-like processing embodied in cells using the walking behavior of Euplotes eurystomus, a ciliate that walks across surfaces using fourteen motile appendages (cirri). We found that cellular walking entails regulated transitions among a discrete set of gait states. The set of observed transitions decomposes into a small group of high-probability, temporally irreversible transitions and a large group of low-probability, time-symmetric transitions, thus revealing stereotypy in the sequential patterns of state transitions. Simulations and experiments suggest that the sequential logic of the gait is functionally important. Taken together, these findings implicate a finite-state-machine-like process. Cirri are connected by microtubule bundles (fibers), and we found that the dynamics of cirri involved in different state transitions are associated with the structure of the fiber system. Perturbative experiments revealed that the fibers mediate gait coordination, suggesting a mechanical basis of gait control.
细胞是复杂的生化系统，其行为源于众多分子成分之间的相互作用。计算通常被作为一种探索细胞复杂性的通用框架。然而，目前尚不清楚细胞如何体现计算过程，以便计算理论（包括有限状态机模型）能够得到有效应用。在这里，我们利用游仆虫（Euplotes eurystomus）的行走行为来展示细胞中类似有限状态机的处理方式，这种纤毛虫使用十四根运动附属物（纤毛）在表面上行走。我们发现细胞行走涉及到离散的步态状态之间的有规律的转换。观察到的转换集可以分解为一小组高概率、时间不可逆的转换和一大组低概率、时间对称的转换，从而揭示了状态转换序列模式的刻板性。模拟和实验表明，步态的顺序逻辑具有重要的功能意义。总的来说，这些发现表明存在类似有限状态机的过程。纤毛由微管束（纤维）连接，我们发现不同状态转换中涉及的纤毛的动力学与纤维系统的结构有关。微扰实验揭示了纤维介导了步态协调，这表明步态控制有一个机械基础。
