How do animals regrow their limbs? And why can't humans do it? - Jessica Whited

翻译人员: Tianyun Liu 校对人员: suya f.

For some animals, losing a limb is a decidedly permanent affair.

对于某些动物来说，失去四肢 绝对是一件永久的事情。

But for salamanders, particularly axolotls,

但是对于火蜥蜴， 尤其是对蝾螈来说，

amputation is just a temporary affliction.

截肢只是一种暂时的痛苦。

Not only can they grow back entire limbs in as little as six weeks,

它们不仅可以在短短 六周内恢复整个四肢，

they can also regenerate heart and even brain tissue.

还可以再生心脏 甚至脑组织。

So how does this astonishing adaptation work?

那么，这种惊人的 适应力是如何运作的？

Regardless of regeneration,

不管再生如何，

every limbed creature had to grow their arms and legs at some point.

每个四肢生物都必须在某个时候 长出自己的手臂和腿。

And whether that process starts in the womb or the world,

而且，无论这个过程是从子宫 还是出生后开始的，

it almost always begins with little bumps called limb buds.

它几乎总是从称为肢芽开始生长的。

These buds are full of progenitor cells—

这些芽充满了祖细胞，

a cornucopia of cell types that can differentiate into various tissues,

这是一种细胞类型的聚宝盆， 可以分化成各种组织，

including muscles, cartilage, ligaments, and tendons.

包括肌肉、软骨、韧带和肌腱。

Some of these progenitors are stem cells,

其中一些祖细胞是干细胞，

capable of developing into a range of specialized cells and tissues,

能够发育成一系列特殊的 细胞和组织，

while others are merely derived from stem cells.

而另一些则仅来自干细胞。

But in either case, the progenitors differentiate and multiply rapidly

但无论哪种情况，祖细胞都会

as the limb bud develops.

随着肢芽的发育而迅速分化和繁殖。

Nerves grow into the limb from nearby cell bodies

神经从附近的细胞体生长到四肢，

and a network of blood vessels form which fuel the process with oxygen.

形成血管网络， 为这一过程提供氧气。

Eventually, that tiny bud grows into a full infant limb.

最终，那个肢芽 成了满满的婴儿四肢。

Most salamanders, including axolotls, develop their limbs in the same way.

大多数火蜥蜴，包括蝾螈， 其四肢发育方式相同。

But unlike other animals, they can also start this process all over again

但是与其他动物不同，

if they need to.

如果需要，它们也可以重新 开始这个过程。

When salamanders lose a limb,

当蜥蜴失去肢体时，

surrounding skin cells quickly surge across the wound’s surface.

周围的皮肤细胞会 迅速涌过伤口表面。

This new layer of skin is called the wound epidermis,

这种新的皮肤层被称为伤口表皮，

and once established, it signals cells in the underlying limb stump

一旦受伤，它就会向下肢残端 中的细胞发出信号，

to undergo something called dedifferentiation.

要求他们进行所谓的分化。

This process reverts nearby cells from fully developed limb tissues

这个过程将附近的细胞 从完全发育的肢体组织

back into earlier, less specialized progenitor cells.

恢复为早期的、 不太专业的祖细胞。

At the same time, the peripheral nervous system fires up stem cells

同时，周围神经 系统会激发火蜥蜴

throughout the salamander’s body.

全身的干细胞。

This would be impossible for most multicellular organisms,

对于大多数多细胞生物来说， 这是不可能的，

whose stem cells typically lose their regenerative capacity with age.

它们的干细胞通常会随着 年龄的增长而失去再生能力。

But when salamander stem cells near the injury get the right signal,

但是，当蜥蜴受伤处附近的 干细胞获得正确的信号时，

they reactivate and start multiplying.

它们就会重新激活并开始繁殖。

Researchers don’t know what ratio of stem cells

研究人员不知道干细胞

and dedifferentiated progenitor cells regeneration requires.

和去分化的祖细胞 再生需要什么比例。

But we do know these cells come together

但是我们确实知道这些细胞聚集在一起

to form the most important part of the process: the blastema.

构成了该过程中最重要的部分：芽基。

This structure is almost identical to a limb bud—

这种结构几乎与肢芽相同

the primary difference is that it’s made of recycled, repurposed cells,

主要区别在于它是由回收的、 再利用的细胞

and potentially reserved cells, rather than completely new ones.

以及可能保留的细胞组成的， 而不是全新的细胞。

Beyond that, blastemas and limb buds have the same mission:

除此之外，囊肿和肢芽 具有相同的使命：

to make thousands of new cells and organize them

制造成千上万个新细胞，并将它们组织

into the muscle, bone, skin, and nerve tissue

成四肢功能所需的

required for a functional limb.

肌肉、骨骼、皮肤和神经组织。

As this process unfolds, nerves and blood vessels spanning the injury site

随着这一过程的展开， 横跨损伤部位的神经和血管

transmit nutrition and oxygen.

会传递营养和氧气。

Over several weeks, the stump will steadily grow

在几周内，肢芽将稳步长出具有

a miniature limb with translucent skin.

半透明皮肤的微型肢体。

And when the process is complete,

而且，当过程完成后，

not only will the limb match the rest of the salamander,

不仅肢体会与火蜥蜴的其余部分相匹配，

there won't even be a scar.

甚至不会有疤痕。

The relationship between scarring and regeneration

疤痕和再生之间的关系只是

is just one of this processes’ many mysteries.

这个过程的众多奥秘之一。

Scientists are still tracking salamander cells on the molecular level

科学家们仍在分子层面上追踪蜥蜴细胞，

to determine how they revert from a mature stage into a regenerative one.

以确定它们是如何从 成熟阶段恢复到再生阶段的。

And research into transplanting blastema cells investigates

对芽基细胞移植的 研究调查了其他动物

how other animals might replicate this reconstructive wizardry.

如何复制 这种重建魔法。

We also don’t understand how salamanders’ bodies know

我们也不明白 火蜥蜴的身体

what part of the limb has been lost or how much needs to be regrown.

是怎么知道肢体的哪一部分 已经失去或者有多少需要再生。

One theory is that blastema cells have a form of positional memory,

一种理论认为，芽基细胞具有 一种位置记忆形式，

allowing them to determine how much to grow in relation to one another.

这使它们能够确定相互之间生长多少。

And it’s equally important to understand how these limbs know when to stop growing

同样重要的是要了解这些四肢 如何知道何时停止生长，

to prevent overdevelopment, like in cancerous tumors.

以防止过度发育， 例如癌性肿瘤。

But one of regenerations essential ingredients doesn’t belong solely

但是，再生的 必需成分之一并不仅仅

to salamanders: the blastema.

属于火蜥蜴：芽基。

Deer antlers use a similar healing tissue to regenerate each year,

鹿角每年都会使用 类似的愈合组织进行再生，

even though their skin scars like ours.

尽管它们的皮肤疤痕像我们一样。

Spiny mice can also restore skin, hair, and some other appendages scar-free.

多刺老鼠还可以使皮肤、 头发和其他一些附属物恢复无疤痕。

And even humans can regenerate the tips of our fingers and toes

甚至人类也可以以惊 人的相似方式再生我们的

in a surprisingly similar manner.

手指和脚趾尖。

We still don’t know whether this ability is tied

我们仍然不知道 这种能力是和

to our shared ancestry with salamanders

我们与火蜥蜴的共同祖先有关， 还是由不同的

or fueled by distinct biological mechanisms.

生物机制推动的。

But with time and research,

但是随着时间的推移和研究，

who knows what evolutionary knowledge we might grow back.

谁知道我们会重新发现 出什么样的进化知识。