What Was Observed? (Introduction)

• Left-right asymmetry (chirality) is a common feature in both animals and plants, affecting their organs and behaviors.
• Scientists wanted to understand how this left-right bias occurs in organisms, especially in unicellular organisms.
• In this study, the slime mold *Physarum polycephalum* was used as a model organism to investigate left-right bias in growth.
• In a T-shape test, the slime mold consistently turned right in over 74% of trials, revealing an inherent left-right asymmetry.
• This discovery is the first to show consistent laterality (preference for turning one direction) in a member of the fungi kingdom.
• The exact mechanism behind why the slime mold prefers turning right is still unknown.

What is Left-Right Asymmetry (Chirality)?

• Chirality refers to the asymmetry of an object or organism, meaning that one side is a mirror image of the other.
• In animals, this is seen in the placement of organs like the heart and lungs, which are not symmetrical.
• In unicellular organisms, chirality can affect how the cell grows and interacts with its environment.
• Left-right asymmetry is critical for normal development, and defects can lead to serious health problems in humans.

How Was the Experiment Conducted? (Methods)

• The researchers tested the slime mold’s growth behavior in two different substrates: agar plates and filter paper.
• The T-shape used in the experiment had a vertical channel (5 mm wide and 20 mm long) and a horizontal channel (5 mm wide and 30 mm long).
• The slime mold was placed at the bottom of the vertical channel, and the experiment was considered complete when the mold reached the end of the horizontal channel.
• Experiments were conducted in complete darkness to avoid external environmental factors affecting the results.
• A total of 120 experiments were performed—60 on agar and 60 on filter paper substrates.

What Were the Results? (Results)

• In 74% of the trials on agar and 78% on filter paper, the slime mold turned right when it reached the horizontal part of the T-shape.
• Only 15% (agar) and 8% (filter paper) of the trials showed the mold turning left.
• Statistical analysis confirmed that the slime mold showed a significant preference for turning right in both types of substrates.
• The mold’s growth behavior remained consistent regardless of the type of substrate, suggesting that the right-turning preference is intrinsic to the organism.

What Did the Researchers Find? (Discussion)

• The consistent right-turning behavior in the slime mold is similar to lateralized behaviors observed in other organisms like planaria, sperm, and even some mammals.
• The researchers believe that this behavior might be linked to the symmetry-breaking mechanisms in the cell’s cytoskeleton, a system that helps cells maintain their shape and structure.
• The finding of chirality in the slime mold suggests that asymmetry is an ancient feature, present across multiple kingdoms of life, not just in animals and plants.
• The preference for turning right could help the slime mold navigate complex environments, similar to how the “right-hand rule” works in maze-solving algorithms.
• Researchers suggest that this right-turn preference might provide an evolutionary advantage by helping the slime mold solve mazes or find food more efficiently, though further studies are needed to confirm this.

What is the Role of the Cytoskeleton in Asymmetry?

• The cytoskeleton is a network of protein fibers inside the cell that gives the cell structure and shape.
• In this study, the cytoskeleton’s role in creating left-right asymmetry was highlighted, as the cytoskeleton’s components may help determine the direction of the slime mold’s growth.
• Research suggests that the actin filaments in the cytoskeleton might rotate in a certain direction, possibly contributing to the right-turning bias observed in the slime mold.
• Understanding how the cytoskeleton works in this context could help explain how left-right asymmetries are generated in other organisms.

Why Does the Slime Mold Prefer to Turn Right? (Theories)

• One theory is that the right-turning bias may help the slime mold solve mazes more efficiently by reducing the time it takes to explore an unknown environment.
• This is similar to a strategy used in robotics called the “wall follower” algorithm, where an agent follows one side of a maze to find the exit.
• The right-turning preference might also be due to a mechanism involving the actin filaments in the cytoskeleton, which may rotate in a specific direction.
• However, researchers are still not sure why the slime mold doesn’t move in circles or why it turns specifically to the right when it encounters an obstacle.

Key Conclusions (Discussion)

• The discovery of consistent left-right asymmetry in *Physarum polycephalum* is important because it extends the understanding of chirality beyond animals and plants to fungi.
• This suggests that the ability to generate asymmetry might be a fundamental characteristic shared across all life forms.
• Further studies are needed to uncover the exact mechanisms behind the slime mold’s right-turning behavior and its evolutionary significance.

观察到了什么？ (引言)

• 左-右非对称（手性）是动物和植物中普遍存在的特征，影响它们的器官和行为。
• 科学家们想要了解这种左-右偏向是如何在有机体中发生的，尤其是在单细胞有机体中。
• 在这项研究中，使用粘菌 *Physarum polycephalum* 作为模型有机体，研究其生长中的左-右偏向。
• 在T形实验中，粘菌在超过74%的试验中持续向右转，揭示了其固有的左-右非对称性。
• 这是第一次显示真菌界中存在一致的偏向性（偏向某一方向转动）。
• 目前还不清楚粘菌为什么更喜欢向右转的确切机制。

什么是左-右非对称（手性）？

• 手性指的是物体或有机体的非对称性，即一侧是另一侧的镜像。
• 在动物中，这可以表现为器官如心脏和肺的位置，这些器官不对称。
• 在单细胞有机体中，手性可以影响细胞的生长方式及其与环境的互动。
• 左-右非对称对于正常发育至关重要，缺陷可能导致人类健康问题。

实验是如何进行的？ (方法)

• 研究人员测试了粘菌在两种不同基质上的生长行为：琼脂板和滤纸。
• 实验中使用的T形结构有一个垂直通道（5毫米宽，20毫米长）和一个水平通道（5毫米宽，30毫米长）。
• 粘菌被放置在垂直通道的底部，实验完成的标准是粘菌到达水平通道的末端。
• 所有实验都在完全黑暗的环境中进行，以避免外部环境因素影响结果。
• 共进行了120个实验，60个在琼脂基质上，60个在滤纸基质上。

结果是什么？ (结果)

• 在琼脂上74%的实验和在滤纸上78%的实验中，粘菌在遇到水平部分时向右转。
• 仅有15%（琼脂）和8%（滤纸）的实验中，粘菌向左转。
• 统计分析确认粘菌在两种基质上均显示出明显的向右转的偏向性。
• 无论使用哪种基质，粘菌的生长行为保持一致，表明其偏向性是有机体固有的。

研究人员发现了什么？ (讨论)

• 粘菌表现出的持续向右转的行为与其他有机体（如涡虫、精子和一些哺乳动物）中的侧化行为相似。
• 研究人员认为这种行为可能与细胞骨架中生成非对称性的机制有关，这是一种帮助细胞保持形状和结构的系统。
• 在粘菌中发现的手性表明，非对称性是一个古老的特征，存在于生命的多个王国，而不仅仅局限于动物和植物。
• 向右转的偏向性可能帮助粘菌更有效地导航复杂环境，类似于“右手规则”在迷宫求解中的应用。
• 研究人员认为，这种右转的偏向性可能为粘菌在迷宫中寻找出口或寻找食物提供了进化优势，尽管还需要进一步的研究来确认这一点。

细胞骨架在非对称性中的作用是什么？

• 细胞骨架是细胞内部的蛋白纤维网络，赋予细胞结构和形状。
• 在这项研究中，细胞骨架在生成左-右非对称性中的作用被强调，因为细胞骨架的组成部分可能有助于确定粘菌生长的方向。
• 研究表明，细胞骨架中的肌动蛋白丝可能以特定的方向旋转，这可能有助于解释粘菌右转偏向的现象。
• 了解细胞骨架在这一背景下的工作原理，可以帮助解释其他有机体中如何产生左-右非对称性。

为什么粘菌偏向右转？ (理论)

• 一种理论认为，右转偏向性可能帮助粘菌在探索未知环境时提高效率，减少探索时间。
• 这类似于机器人学中使用的“墙随者”算法，在该算法中，代理会沿着迷宫的一侧移动以找到出口。
• 右转偏向性也可能与细胞骨架中的肌动蛋白丝有关，后者可能以特定的方向旋转。
• 然而，研究人员仍然不确定为什么粘菌不在圆圈中移动，或者为什么它在遇到障碍物时特定地向右转。

关键结论 (讨论)

• 在 *Physarum polycephalum* 中发现一致的左-右非对称性，这一发现很重要，因为它将手性的理解扩展到了真菌界，超出了动物和植物的范畴。
• 这表明，生成非对称性的能力可能是所有生命形式共有的基本特征。
• 需要进一步的研究来揭示粘菌右转行为的确切机制及其进化意义。