No Battle Scars

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No battle scars

A tiny crustacean seems to have perfected regenerating its limbs.
Join Alba as she investigates this down to a cellular level.

Our Body

Broken bones mend themselves,
severe injuries heal,

and, over time,
all that remains of it
are the scars we carry.

Our bodies are amazing!

There is, however, one thing that our body
is just not equipped to do:

There is, however, one thing that our body
is just not equipped to do:


Grow back body parts.

Regeneration

It is the ability that some animals have to re-grow body parts.

Regeneration

It is the ability that some animals have to re-grow body parts.


To us, it is such an exotic trait, but it is indeed more common in animals than we tend to think.

Regeneration in lizards

Lizards may injure their tail and have to regenerate it. And each time, we see them regenerate a fully functional replica.

Regeneration in lizards

Lizards may injure their tail and have to regenerate it. And each time, we see them regenerate a fully functional replica.


But on closer inspection, we can spot defects.

In fact, the bony vertebrae of the lizard's tail is replaced by cartilage in the regenerated tail.

In some other cases,
the defects are more striking.

Regeneration in frogs

Tadpoles can regenerate their limbs perfectly.

Although, after they metamorph into frogs,
the same regenerated structure no longer
resembles the original one!

There is a tiny crustacean who seems to be able to regenerate perfect replica of its limbs.

There is a tiny crustacean who seems to be able to regenerate perfect replica of its limbs.


How is that possible?

There is a tiny crustacean who seems to be able to regenerate perfect replica of its limbs.

How is that possible?


And why can this small shrimp regenerate perfectly while other animals cannot?

Alba Almazán (CC-BY-NC-ND)

Parhyale hawaiensis

This is Parhyale.

It does as other marine creatures do:
swimming, eating, mating...

Alba Almazán (CC-BY-NC-ND)

...but, like many other animals in nature,
it is vulnerable to predators and sometimes
even its own neighbours.

Yikes!

Alba Almazán (CC-BY-NC-ND)

These are tense situations, and Parhyale can sometimes lose a whole limb!

These are tense situations, and Parhyale can sometimes lose a whole limb!


But that's not really a problem for it, because it can simply regrow a seemingly perfect replicate.

These are tense situations, and Parhyale can sometimes lose a whole limb!

But that's not really a problem for it, because it can simply regrow a seemingly perfect replicate.


Leaving no trace of the battle injury.

Alba Almazán

Our researcher, from the Averof lab in Lyon,
and her colleagues are pushing their boundaries to test Parhyale's regenerative perfection;

Can this tiny crustacean really regenerate a
replicate down to a T?

Lets begin by comparing images of Parhyale‘s
uninjured limb with a regenerated one.

Uninjured limb
Regenerated limb after 3 weeks
Regenerated limb - 6 months

In just 3 weeks, it has grown a miniature replica of a limb.

Uninjured limb
Regenerated limb after 3 weeks
Regenerated limb - 6 months

In 6 months, the limb looks identical!

Uninjured limb
Regenerated limb after 3 weeks
Regenerated limb - 6 months

We just compared simple snapshots of
the regenerated limb with the uninjured limb.

And physically the limbs look identical.

What's going on inside Parhyale to regenerate this identical limb?

What's going on inside Parhyale to regenerate this identical limb?


To answer this question, we need to peek
inside the animal and observe the process on a cellular level.

What's going on inside Parhyale to regenerate this identical limb?

To answer this question, we need to peek
inside the animal and observe the process on a cellular level.


Today, Alba's colleagues can observe
this process live, in extraordinary detail.

Live cell imaging

This technique revolutionised biology in the end of the 20th century, finally allowing us to observe the living cellular world.

Let's take a look at what we can observe!

Çağrı Çevrim (CC-BY-NC-ND)

What you see moving around are nuclei, doing many different things.

We know that these nuclei correspond to neurons, epidermal cells, muscle cells and many other types of cells needed by the limb.

Çağrı Çevrim (CC-BY-NC-ND)

Alba is asking: Does Parhyale regenerate all the different types of cells present in the uninjured limb?

Is the regeneration perfect, even at the cellular level?

Çağrı Çevrim (CC-BY-NC-ND)

UMAP

Alba is able to visualise the different types of cells in the limb onto a graph, called a UMAP.

UMAP

Alba is able to visualise the different types of cells in the limb onto a graph, called a UMAP.


Lets take a look at the UMAP for the uninjured limb.

UMAP of uninjured limb

Each dot represents a cell, and they are grouped by how similar they are in their function.

Alba was able to identify muscle cells, nerve cells, blood cells and a whole range of other types of cells.


Now let's bring up the UMAP for the regenerated limb.

Alba Almazán (CC-BY-NC-ND)
UMAP of uninjured limb

Each dot represents a cell, and they are grouped by how similar they are in their function.

Alba was able to identify muscle cells, nerve cells, blood cells and a whole range of other types of cells.


Now let's bring up the UMAP for the regenerated limb.

Alba Almazán (CC-BY-NC-ND)
UMAP of uninjured limb

Each dot represents a cell, and they are grouped by how similar they are in their function.

Alba was able to identify muscle cells, nerve cells, blood cells and a whole range of other types of cells.

Now lets bring up the U-Map for the regenerated limb.

UMAP of regenerated limb
The UMAPS look identical!
The UMAPS look identical!
The UMAPS look identical!
The UMAPS look identical!

The regenerated limb has all the different types of cells restored in it.

The UMAPS look identical!
The UMAPS look identical!

The regenerated limb has all the different types of cells restored in it.


This regeneration process is unbelievably flawless!

The UMAPS look identical!
The UMAPS look identical!

How can Pahryale recreate such a perfect replica of its limb?

The UMAPS look identical!
The UMAPS look identical!

How can Pahryale recreate such a perfect replica of its limb?


Are there different ways to create exactly the same limb?

The UMAPS look identical!
The UMAPS look identical!

How can Pahryale recreate such a perfect replica of its limb?

Are there different ways to create exactly the same limb?


Or is Parhyale mimicking the same mechanisms that it used for building a limb when it first grew into an adult?

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