What Was Observed? (Introduction)

• Scientists wanted to understand how an animal’s limbs grow and regenerate, particularly focusing on how the size of the limbs matches the size of the body.
• Axolotls, a type of salamander, were used for this study because they can regenerate lost limbs throughout their lives.
• The experiment involved repeatedly removing the limb buds (the initial stage of limb growth) of axolotls and observing how this affected their limb size and regeneration ability.
• After about 10 months, the axolotls’ limbs were smaller than normal, even though their bodies had grown to normal size. This effect lasted throughout their lives, indicating a permanent change in how the limbs developed and regenerated.

What is Limb Bud Removal?

• A limb bud is the early stage of a developing limb, similar to the beginning of a limb “growing out” from the body.
• By repeatedly removing the limb buds and forcing the axolotls to regrow them, scientists hoped to see if they could alter the size of the limbs compared to the body.

What Happened in the Experiment? (Methods)

• The experiment began with young axolotls, and their limb buds were removed every few days for several months to see how repeated removal affected limb growth.
• Initially, when the limb buds were removed up to 10 times, most of the axolotls were able to grow normal-sized limbs again.
• However, after many more rounds of limb bud removal (around 36 times), the axolotls could not grow full-sized limbs anymore, and their limbs became much smaller than those of normal siblings.

Miniaturization of Limbs

• The miniaturized limbs had all the correct bones and muscle structures but were significantly smaller compared to normal limbs of the same age.
• Even after these small limbs grew for a long time, they remained smaller than the limbs of the control group that did not undergo repeated bud removal.
• Interestingly, the axolotls could still use their miniaturized limbs for basic functions like swimming, even though the limbs were much smaller than normal.

Why Were the Limbs Miniaturized? (Possible Reasons)

• One possible reason for the miniaturization is that the nerve supply to the limbs was reduced. Nerves play an important role in the growth of limbs.
• Without enough nerves, the limbs may not grow to their full size, which may be what happened in this case.
• The reduced number of nerves might have affected the size of the regenerated limbs, leading to smaller limbs even after they were amputated and regrew.

What Happened After Amputation? (Regeneration Results)

• Even though the miniaturized limbs were smaller, they could still regenerate new limbs after being amputated.
• However, the new limbs that regenerated from these miniaturized limbs were also smaller, showing that the miniaturization was a permanent feature of the limb.
• After amputation, about 83% of the miniaturized limbs regenerated correctly with four digits, but the bones in the regenerated limbs were sometimes incomplete.

Key Conclusions (Discussion)

• The repeated removal of limb buds caused the axolotls to permanently develop smaller limbs, showing that the size of an appendage is influenced by factors beyond just the animal’s body size.
• The study demonstrated that the size of limbs could be decoupled from the size of the body in these animals, which opens up new ways to study how the size of organs is determined during development and regeneration.
• It was found that the lack of nerves in the limbs likely contributed to their miniaturization.
• This experiment provides insights into how appendage size is controlled and how it can be altered by external factors like repeated removal of limb buds.

What Can We Learn from This Study?

• This research helps us understand how limb size is regulated and what happens when the normal process is interrupted.
• The results suggest that manipulating the size of organs, like limbs, could be a key to advancing regenerative medicine and understanding how growth and regeneration work.

观察到什么？ (引言)

• 科学家们想要了解动物的四肢如何生长和再生，特别是四肢大小如何与身体大小匹配。
• 本研究使用了墨西哥大蜥蜴（Axolotl），因为它们一生中可以不断再生失去的四肢。
• 实验中，科学家们反复去除墨西哥大蜥蜴的肢芽（肢体生长的早期阶段），观察这如何影响其四肢的大小和再生能力。
• 经过大约10个月的实验，发现这些动物的四肢变得比正常的小，尽管它们的身体保持正常大小。这个变化持续了一生，意味着四肢的发育和再生发生了永久性变化。

什么是肢芽移除？

• 肢芽是发育中四肢的早期阶段，可以看作是四肢从身体中“长出来”的开始。
• 通过反复移除肢芽并迫使墨西哥大蜥蜴重新长出肢体，科学家们希望能改变四肢的大小。

实验中发生了什么？ (方法)

• 实验从年轻的墨西哥大蜥蜴开始，肢芽每隔几天就会被移除几个月，以观察反复移除肢芽对四肢生长的影响。
• 最初，当肢芽被移除最多10次时，大多数墨西哥大蜥蜴能够重新生长正常大小的四肢。
• 然而，在更多轮的肢芽移除（大约36次）之后，墨西哥大蜥蜴不能再生长完整的四肢，它们的四肢变得比正常的小得多。

四肢迷你化

• 迷你化的四肢有着正常的骨骼和肌肉结构，但比正常四肢小得多。
• 即使这些小四肢生长了很长时间，它们依然比没有经历过肢芽移除的对照组的四肢小。
• 有趣的是，墨西哥大蜥蜴仍然能用它们的迷你化四肢进行基本的功能，比如游泳，尽管这些四肢比正常小得多。

为什么四肢会迷你化？ (可能原因)

• 迷你化的原因之一可能是四肢的神经供应减少。神经在四肢的生长中起着重要作用。
• 没有足够的神经，四肢可能无法长到它们的正常大小，这可能是发生这种现象的原因。
• 神经数量的减少可能会影响再生四肢的大小，导致这些四肢在重新生长时变得更小。

截肢后发生了什么？ (再生结果)

• 即使迷你化的四肢变小，它们仍然能够在截肢后再生新的四肢。
• 然而，从这些迷你化四肢再生的新四肢依然比正常四肢小，证明迷你化是四肢的永久性特征。
• 截肢后，大约83%的迷你化四肢成功再生并拥有四个数字，尽管再生的骨骼有时不完整。

关键结论 (讨论)

• 肢芽的反复移除导致墨西哥大蜥蜴永久性地发展出更小的四肢，表明四肢的大小受多个因素的影响，远不止动物的身体大小。
• 这项研究表明，四肢的大小可以脱离身体的大小独立控制，这为研究器官大小如何决定和再生提供了新的途径。
• 研究发现神经的缺乏可能是导致四肢迷你化的原因。
• 这项实验为我们提供了如何控制和改变器官大小的重要见解。

我们从这项研究中学到了什么？

• 这项研究帮助我们理解了四肢是如何调控大小的，并且当正常过程受到干扰时会发生什么。
• 结果表明，改变器官大小可能是推动再生医学发展的关键，也有助于理解生长和再生的过程。