- I've talked about symbiodinium many times on this channel.
We know that these tiny little single-celled dinoflagellates
provide a lot of the energy that the corals need,
and those corals house them in their tissues.
We know that the coral can expel the dinoflagellates
when they're stressed, it's called coral bleaching.
We've also talked about how coral
is able to take in the dinoflagellates from the water,
and that's how baby newborn freshly settled coral
gets their first set of these critical symbiotic organisms.
But if corals are just picking up cells from the water,
how do they ensure that they're getting only good cells?
How do they prevent disease-causing cells from coming in,
cells that could make them sick?
Hi, guys and girls, I'm ReefMan.
And this week we'll be talking about a paper
that was just published in June of 2020 of Nature,
and it's got the title "Lineage Dynamics
of the Endosymbiotic Cell Type in the Soft Coral Xenia."
The paper is open access,
and as always, there's a link down below, so check it out,
you get a lot more information
if you want the full details
or if there's all that kind of stuff on the research.
First off, maybe that title is a little bit confusing.
I thought it was.
So let's break it down a little bit.
What is or what are lineage dynamics?
Well, to be honest, I'm not sure.
I tried to find a good definition, couldn't really find one.
Cellular dynamics is a study of just how the cells work
and how it changes in response to stimuli.
A cell lineage is just a cell over time
or maybe a group of cells kept over time.
So I'm pretty sure that lineage dynamics
is just looking at the structures
and the things going on in cells over time.
And if you've got a better way to explain that,
maybe you're a biologist, drop us a comment below,
I'd be happy to get a better definition.
I'm not a biologist by training,
although I do play one on YouTube.
And then the second thing
that might be confusing, endosymbiosis, what is that?
That one I did know, most coral gets a lot of food
from those dinoflagellates that I was talking about,
they're tiny little things that can live on their own,
but they can also live in the tissue of the coral,
that's endosymbiosis.
Whenever two organisms live together
where one is inside the other, they're endosymbionts.
So this paper is looking at the cells in Xenia coral,
which contain dinoflagellates,
and then looking at how they actually make that work
on a cellular level.
This is something
that science has been trying to figure out for a while,
and so it's really cool
to see a paper actually explaining it.
I'm sure there's gonna be a lot more papers on this
because this one really just introduces the core concepts
and sort of proves it out,
but that raises a lot more questions
that really can only be answered now that we have this work
as a foundation to build off of.
Corals collect Symbiodinium algae through feeding,
and then they end up in the cells
that line their digestive tract,
those are called the gastrodermis,
(mumbles) the gastrodermis and this is a tissue there.
It turns out that those cells can identify specific cells
that are gonna be good for the coral,
and they also contain genes
that let them modulate the immune response
that you'd expect to see
when a foreign cell enters one of your body cells,
that's how you fight off an infection.
The research team did a lot of RNA sequencing
to find the answers that are in their paper.
In fact, they found that Xenia has about 29,015 genes,
that's a similar number as other cnidarians,
other corals and jellyfish, things like that.
For comparison, you and I,
well, we have somewhere between 20 and 25,000 genes,
so Xenia actually has more than us.
These genes are used to produce all sorts of proteins
and things that we and corals need for our day-to-day lives.
Using the genes found inside cells,
the team sorted the cells of the Xenia
into 16 different groups.
Not all cells have all genes.
For example, your brain tissue can't make digestive fluid
like your stomach lining can.
So by segregating about into groups,
they could more easily look at related cells
based on the genes.
To find cells that were involved
in the dinoflagellates to begin with,
the team used the simple fact
that dinoflagellates fluoresce.
They could use this to sort the cells into different groups
where some of them contained dinoflagellates
and some of them didn't.
Between 2 and 6% of cells in a given Xenia
are gonna contain dinoflagellates,
and cells found in the tentacles actually have the most.
Cells that did contain dinoflagellates
had genes that were able to recognize the other cells
and aid in phagocytosis,
which is when one cell engulfs another,
and your white blood cells actually do that as well.
And they also had genes
that could control the coral's immune response.
So these cells can identify the proper dinoflagellate algaes
to grab out of the water,
they can grab them from the water
in the digestive tract of the coral,
and then they can make sure that the coral's immune system
doesn't kill the algae,
which, of course, would make the whole thing useless
in the first place.
It's important to understand also,
these cells and the dinoflagellates
are almost the same size.
So, if you have the cell and the dinoflagellate,
when the cell surrounds
and brings the dinoflagellates inside,
it's got to almost double in size.
That's no simple feat for a cell to do.
And that's why they have genes that make it possible.
The team also identified five individual stages
that these cells seem to go through,
starting with a cell without any symbionts in it
called pre-endosymbiotic,
all the way through mature cells
that contain dinoflagellates, that's stage three,
and up to stage five,
where the cells have lost their symbionts.
And that's the lineage dynamic
that the title is referring to.
This is really the first paper
and the first research that I'm aware of
that actually identifies these cells
and looks at how it all works,
sets up that lineage dynamic,
looks at the genes in them that make it all work.
This is really amazing research
and I'm really glad that it is published
and open access in Nature
so that we can all read it and learn from it.
A lot of times this stuff is kept sort of under lock and key
in academic libraries and understanding how this works
is gonna unlock so many more avenues for research.
Now that we know something about the cells
and how they work,
maybe we can find a way to use the cells
to help combat coral reef bleaching
because those same cells are involved in that
when they expel the dinoflagellates.
I hope you enjoyed the video.
The paper is linked down below.
Check it out if you're interested,
there's a lot more detail that I didn't go into.
Don't forget to subscribe, be kind to each other,
have a fantastic day, bye.