Bdelloid rotifers: a new biological model? | Karine Van Doninck | TEDxUNamur

All living beings are connected and share a common ancestor - the tree of life. Life involves change. It comprises those processes such as reproduction, variation and inheritance. Reproduction is vital and occurs in various modes, sexual reproduction being the dominant one in the eukaryotic kingdom. Nevertheless, several types of reproductive modes evolved and persist.

One of the main interests of the Karine Van Doninck lab is to tackle fundamental questions related to the evolution of asexual reproductive modes and to understand the factors contributing to genomic variation and adaptation. Karine studies especially bdelloid rotifers employing a specific mode of asexual reproduction. Rotifers from the Class Bdelloidea are common microscopic metazoans that appear to be obligate ancient asexuals (“all-female asexuality”). They have a worldwide distribution, occurring preferentially in ephemerally aquatic habitats such as mosses and lichens because they can survive desiccation at any stage of their life cycle.

This talk was given at a TEDx event using the TED conference format but independently organized by a local community. Learn more at https://www.ted.com/tedx

Good evening.

Here you see a little petri dish
that we use in the lab

with a dry leaf, completely dry,

and on there, there are females.

Why do I say females?

Because that's their way of life:
They live and evolve without males;

they got rid of males.

And also, they are dry.

They can dry up,
and we can wait for years,

put them in the freezer,
and get them back.

Tonight we will do a live experiment
with one of my scientists, Boris,

to resurrect these animals for you,

these females.

Thanks, Boris.

So look around you.

There is an amazing diversity
of living organisms on this planet,

from bacteria to fungi to plants
to animals to human -

nothing looks alike.

But do you know that all this diversity
arose once from a universal ancestor

around 3.5 billion years ago?

And this ancestor of all living organisms
was a single simple cell,

something like a bacterium.

But how do we know that all life
has evolved from a single cell?

We know this because we all
share the same alphabet;

we have the same DNA code.

DNA is a magical molecule of life.

And DNA is only made up
of four chemical building blocks:

cytosine, guanine, adenine, thymine.

So only four letters
that make the whole alphabet of life.

So yes, from bacteria to human,
we only need four letters,

but then, what's our DNA
instruction book looking like?

In each of our cells, we have
around three billion of those letters,

organized on 23 pairs of chromosomes.

So you see here,

it's a compaction of these four letters.

But what makes you different from me
is that these letters change.

These letters change
between all these individuals.

So if we all have the same genetic code,
it means we are all related.

Yes, we are.

We are all cousins from each other.

But then, you may wonder:

How did we evolve to so many complex forms

from such a single cell a long time ago?

And that's when I want you to remember
the card game we have been playing.

What's essential for evolution
is genetic variation,

its changes in these letters.

So these letters change randomly.

And most of these changes are neutral,

they have no effect
on the fitness of the individual,

but if a change is an advantage,
it can be selected.

Remember?

We select if a positive mutation appears.

Why is it selected?

Because the individual gets an advantage

and it might reproduce
more than the others

so the mutation is transmitted.

And we know

that natural selection is cumulative,

that we can accumulate
this positive mutation,

which is important
for adaptation and evolution.

So as I said, during the card game,

there is nothing of intelligence
or a creator out there

for evolution.

And look at cancer development.

Cancer development
is also an evolutionary process;

it follows this same mechanism.

Each of our cells accumulate
randomly these changes, these mutations,

but if one of these normal cells
suddenly gets a growth advantage -

a mutation that gives it a growth
advantage compared to the other cells -

it will start to grow quicker -

an uncontrolled proliferation -

and cancer can occur.

And of course, it's a problem to human.

We know it.

But you know, animals also get cancer.

But do all of them get cancer?

There are a few mysterious species
that don't develop cancer.

What are they?

The most notorious one
is this naked mole rat.

Very cute animal, no?

(Laughter)

For scientists,
it's a very interesting animal.

It's very small. It's like a mouse.

But it lives for 30 years,
and a mouse lives for four years.

What's also interesting is

if you inject the cancer cell
in this animal,

it will not develop.

And why?

Scientists have searched
for this for years

and found that they
have this kind of molecule -

a high molecular mass, hyaluronan;

it's a kind of super sugar -

that is secreted around
the cells of these animals,

and it makes their tissue very elastic.

And why is it important?

Because these animals dig into the soil,
they make these burrows,

and so their tissue
needs to be very elastic.

So it's an adaptation to this.

But what's interesting

is that this molecule,
when it's secreted around the cell,

prevents the cell from dividing
or proliferating further.

So you immediately see

the interesting application
of the discovery of such a molecule.

But if you think this is
the only interesting animal out there,

you’re wrong.

Nature is full of mysterious species,
where we can discover so much.

Nature has been an inspiration
to scientists for so many years.

Like Albert Einstein said,

"We know less than one thousandth of 1%
of what nature has to reveal to us."

And if we start to destroy our nature,

we will not even discover
everything that's out there.

Look at this gecko.

This gecko, we know,
can run quickly on vertical glass.

But how?

How can these animals
adhere so strongly to glass

and then just run on it?

And so, for long,

scientists looked at the molecule:

What kind of molecule is secreted
that makes them like a glue,

like a strong adhesion?

And in fact, by looking at these fingers,

they found there's nothing
of a molecule that is secreted,

but it's a structure.

What they discovered

is that underneath these fingers,
there are these hair-like structures,

millions of them.

And if you look even
at the nanoscopic level,

you see that at the end
of all of these hairs,

you have hundreds of these
spatula-likes structures.

And when these are
in strong contact with glass,

it creates a strong adhesion
just through simple Van der Waals forces,

the simple forces
that make this strong adhesion.

And when they rotate their fingers,

this force releases immediately
and they can run further.

And of course,

laboratories have now been interested
to reconstruct these nano-structures

to make strong adhesives.

And that's what I want to show you:

It's so interesting to study biology
because there's so much to discover,

because there has been
such a long evolution

of all kinds of specimens
with all kinds of different adaptations.

And what has puzzled me is reproduction.

You know that for life,
it's essential to reproduce;

we need to reproduce
or the species will go extinct.

But do you know that sexual reproduction,

the one we all know,

is the queen of problems
in evolutionary biology?

For us scientists, it's really a puzzle.

And why?

Think about all the energy you need
to spend to find a partner,

all the strategies the male's developed

to try to attract a female,
to try to fertilize her,

to the point that there is
a battle of sexes.

Believe me -

a man penis is boring
compared to this insect penis.

This is a penis of a bean weevil,

full of spines,

and the males with the longest spines
are those that fertilize most of the eggs.

Of course, the female cannot
reproduce anymore afterwards,

but at least, the male is sure
he has transmitted his genes.

A look at this fruit fly.

You might have many fruit flies
in summer around your trash bin.

This fruit fly, Drosophila bifurca,

produces giant sperm,
20 times its body size.

It's like, you men,

you would have a sperm
that is twenty times your body size,

like a building of 12 stories.

(Laughter)

Wow!

But at least, when it
transmits this to the female,

the receptacle of the female is filled,

there is no space for another sperm,

so it's sure to transmit its genes.

But then, why did such a complicated mode
of reproduction evolve?

And why is it so omnipresent?

Is it not just simpler to clone yourself?

One individual makes a new individual?

So why is sexual reproduction
so prevalent in nature?

In fact, for us biologists,

sex is just about mixing genetic material
of one individual with another individual

to create each generation
of offsprings that are all different.

And that's a force of sexual reproduction:

It creates every generation
this genetic variability

that is essential for evolution.

So does it mean that animals
that lose sexual reproduction

or that abandon it
or have no sexual reproduction

cannot evolve, cannot adapt?

That's what we thought

until we discovered

what has been called
an evolutionary scandal

or an ancient sexual scandal:

It's a microscopic world of animals,
the bdelloid rotifers.

These are females cloning themselves;
never has any male been discovered.

They exist since millions of years
and we found them everywhere.

And they are not only interesting

because they can reproduce without males
and evolve without males,

we can also dry them out.

I showed you:

We can just take them, here in the park,

a piece of lichen, a dry lichen,
bring it back to the lab,

and what you see -

that's also what you see
on the microscope -

is this dry lichen
and then they are introns.

But when we add water,
they start to live again.

So these animals -

We can dry them out
at any stage in their life,

and we can keep them dry.

We can put them in the -80 freezer.

We can send them
to collaborators in the US,

and if they add water, they live again.

And it's not only one species.

You could think, "Yeah,
but it's just this rare animal."

No, it's more than 400 species
being described

as having diversified
into many morphological forms -

all females reproducing without males,

most of them being able to dry out.

And of course this makes the newspaper:

["Asexual reproduction is possible."]

Yes, it's possible.

But then, of course, you might think,
"How did these females evolve?"

How do they create variability? -

because we know
it's essential for evolution.

So, if they just cloned themselves,
how do they ever evolve and adapt?

And so, as a scientist,

it is important to have
these hypothesis to think of.

So our hypothesis is -

It's easy to work with this animal.

You take a female in the wild,
you start to clone it in the lab,

you have millions of identical females,

we dry them up,

and then, our question was,

"Do these females -

What happens to the genetic
material of these females

when we dry them up?"

We know from bacteria

that drying up breaks
their genetic material into pieces.

Is this also happening in these animals?

And then, what if they don't
repair perfectly these pieces,

is this a way to create variability? -

meaning,

if you replace males by drying up,
you might also evolve.

And so, that's what we tested.

So Boris has designed
a very nice protocol in the lab

to dry them up
with a high survival rate.

And what happened to these females
when they are dried up?

You see, the longer they are dried up,
the more their DNA is broken.

The simpler the gel
and the DNA migrates through it,

the smaller the pieces.

And when we hydrate them,
what you see is that they start to repair.

So they can come out of drying,
they have their broken DNA -

but they can survive
with broken DNA apparently -

and then they start to repair.

And you know,

if you have a cancer cell,

it's known that sometimes
during a division some DNA breaks,

and it repairs this broken DNA
but not perfectly,

and you can have an aggressive
cancer that appears.

What they do in proton therapy is

use proton radiation to completely destroy
the DNA of cancer cells

so the cells get completely broken DNA,
and molecules too.

So we thought if we do
proton radiation to these animals,

what happens?

So we took, again, a female,

we dry it up,

we add proton radiation,

and what happens?

DNA gets completely broken.

And this 800 grays
of proton radiation are huge doses.

There are no living cells
that can survive this.

But what's amazing here is -

you really see the DNA
is completely broken -

when we re-hydrate these females,
99% of them survive.

So they come out of drying
with a completely broken DNA,

without a problem,

and then they start to repair.

And of course, the question is,

"Do they really repair perfectly?

Or do they put all the pieces
of DNA back together

into their 12 chromosomes? -

because we found they had 12 chromosomes -

or is that just creating
some variability?"

So we have here preliminary results
that I'm just showing you tonight,

where we did this experiments,

where we dry them up,

we irradiate them,

and then we look at its genomic structure.

Not going too much into detail,

but what you see here is, for example,

pieces of the ridge
of the genome from a female

before she was radiated or dried up.

Then we dry it up, we irradiate it,

and we look at whether
these pieces come back.

You see here - everything is destroyed,
and whether we get these pieces back -

showing it's stitching back
all these DNA pieces together

into these 12 chromosomes.

So they can do this:

They reconstruct their genome as before,

or at least, that's what
it seems to look like.

And even the descendants
have that same structure

as a parent’s alignment.

So is there no genetic
scrambling going on?

That's possible.

Maybe they don't, indeed,
make a completely new genome;

they keep their genome.

But what we then ask ourselves is:

"How can you survive
when you are irradiated,

because not only your DNA is broken,
but also your molecules must be broken?"

But they must keep
their molecules somehow intact

because you need these molecules
to repair your DNA.

So what do they have?

What's their secret?

What did we find
by sequencing the first genome,

really sequencing the entire
alphabet of this animal?

We found that they have
a huge amount of antioxidants.

Antioxidants are essential

to protect yourself
from these damaged cells.

We all have antioxidants.

That's because our cells
accumulate damages,

a kind of what we call oxidative stress,

and your proteins, your DNA -
everything gets damages.

That's why we get older.

And that's why you put all these creams on
that are full of antioxidants,

to try to prevent the aging of your cells,

but it will not.

But here, these animals
have a huge amount of these antioxidants.

So next time, think about it,

don't buy all these expensive creams
full of antioxidants,

just drink some rotifers.

You find them in the nature
and they might help.

(Laughter)

But of course,

these are all things we discovered,

but as a scientist,

when you discover things,
you have even more questions.

And so recently,

I obtained a grant
from the European Research Council

to really try to demystify
all these mysteries we found.

We found they have
this huge amount of antioxidants,

but are they really effective?

How do they repair this broken genome?

What are the molecules,
the mechanism they have

to repair such a broken genome
to survive drying, freezing?

Then one last thing we discovered is

by sequencing their genome,
we found, among their genetic material,

genetic material
from bacteria, plants, fungi -

so they seem to integrate DNA
from their environment.

And that's of course puzzling.

But we also thought,

If they can integrate this foreign DNA,

can they also integrate DNA
from other females out there,

other rotifers that also dry up?

And the first results we got on this

is that we found some signatures
of DNA exchange between these females,

and we think it's not conventional sex,
because we never found males,

so they are not using the strategy
that all animals do -

a sperm and an ovocyte
to exchange DNA.

So what is the strategy? We have no idea.

We call it sapphomixis -

it's a mixing of genetic
material between females.

And you immediately see here
why it's so beautiful to be a scientist -

you discover a lot,
but you have even more questions.

But what's for sure

is that we have a very interesting
model organism here to understand,

"How can they evolve without males?

How does sapphomixis happen?

And how can they survive
such extreme conditions

as drying up, freezing,
and high doses of radiation?"

There's so much still to discover there.

And one of our next challenges
is to send them to space.

We got a grant from
the European Space Agency

to send, in 2019, rotifers to space, RISE.

Why? Because space is also
an extreme environment.

We have no idea at the moment

what this extreme environment has

as pressure on astronauts
or any living animal.

This is a very interesting
model organism to send out there

and to understand much better
what space is like.

And of course,

I cannot end this presentation
without thanking all the funding

but especially all the people
in my lab - many are here.

This work is never done by one person.

A lab is really a group
of persons working,

tackling these questions.

A lot of frustrations.

They know it better than me right now.

And then, I would like to thank
the rotifer and Boris

with the whole experiment

because thanks to these rotifers,

I'm really happy to go every day,
or almost every day, to my work.

At least, when I know I can do science
and I can work with rotifers,

I'm a happy person.

Thank you.

(Applause)