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The microcosmos is not always a graceful space.
Sometimes an organism just needs to get around the way it gets around, even if that means
looking like a swimming elephant head with a truncated snout at one end and a rat tail
at the other.
Those odd creatures are called Bodonids, single-celled eukaryotes with two flagella that create that
frantic movement.
They belong to a group of flagellated protists called Kinetoplastida, and it was probably
a relief to James, our master of microscopes, that the Kinetoplastids he found had two flagella.
If there was just one flagellum, he would be dealing with the other half of the group:
the Trypanosomatids.
The family Trypanosomatida is made up entirely of parasites that like to infect insects and plants.
But some, like Trypanosoma cruzi, the organism responsible for Chagas disease, can make their
way over to humans via their insect hosts, causing aches and fever and swelling among
a number of other symptoms.
There are some parasitic Bodonids, but those ones tend to be found in fish and snails.
And the family relationship they have with Trypanosomatids has made Bodonids a handy
organism to have around so that we can better understand the diseases their relatives cause.
It’s a nice role for an organism that is sometimes easy to miss against the backdrop
of the microcosmos.
Like if we hadn’t shown you what bodonids look like already, and if we’d opened today’s
episode with this scene...
would you know what you are looking for?
I know I would probably have assumed they were the green almond-shaped organisms, just
because their color and strange shape makes them stand out so much more.
And even in this scene, where there are so many more bodonids to see, they’re just
so secondary to the giant rotifer picking away at their population.
Those other creatures are fascinating and we’ve encountered them plenty of times on
our journey through the microcosmos.
But you know what they don’t have that Bodonids and their fellow kinetoplastids do?
Chainmail.
Yes, chainmail.
But also fine, not actual chainmail.
Bodonids aren’t decorated in metallic loops.
What they have is actually something more unique and fascinating—something that has
changed the way we see the molecules and processes fundamental to life.
Kinetoplastids get their name from this unique chainmail structure.
It’s called the kinetoplast, and it’s found inside their mitochondrion.
The kinetoplast is unique, but its building blocks aren’t:
it’s just DNA.
You know, that double helix found in all of us, that molecule that holds the instructions
for how our cells look and behave.
When scientists were finally able to see the kinetoplast under an electron microscope,
they realized that the DNA inside of it does something kind of funny.
It forms thousands and thousands of tiny little circles, along with around 25 to 50 larger circles.
And those circles of DNA link together, building a structure that, in many kinetoplastids,
looks a lot like chainmail.
Scientists have done all sorts of experiments to learn more about this DNA.
But one of the most important things they’ve learned isn’t about DNA—it’s about DNA’s
single-stranded cousin RNA.
We said earlier that DNA is like the instruction manual that tells our cells what to do.
But an instruction manual is just a stack of paper if no one is around to read it.
So inside of cells, there is a mechanism in place to read that DNA, transcribing it into
a single-stranded genetic material called messenger RNA.
You can think of that RNA as like someone reading aloud from the instruction manual.
After, that messenger RNA’s words get translated into action, producing a protein that can
go on to serve some function in the cell.
That process—DNA transcribed to RNA and then translated into protein—forms what
many of us know as the central dogma of biology.
It is beautiful, it is elegant.
And it is also far too simplistic for what life actually looks like.
There are many ways that process is more complicated than what we originally said, but we’re
here for the kinetoplastids and their strange DNA chain mail.
One of the unusual things researchers in the 1980s noticed as they studied kinetoplast
DNA is that there were genes that almost coded for things we knew they should code for.
The sequences in them created instructions that looked like they should make a particular
protein found in these organisms, but something would be off.
Mutations would shift the instructions slightly, almost as if it were missing key words or
someone had deleted a step in the instruction manual.
But that was in the DNA.
When they studied the RNA, the instructions were suddenly correct again, almost as if
they had been edited to make sense.
In fact, that’s what the researchers would call the process: RNA editing.
This process turned up over and over again in the kinetoplastids.
Nonsensical instructions in the DNA would make sense later thanks to RNA editing, a
biological process poking at the person reading from the manual to correct their final message.
Kinetoplasts aren’t the only organisms to use RNA editing, and it’s not quite clear
what advantages there are to the process.
Perhaps it allows a single gene to encode multiple proteins.
Perhaps it’s a necessary adaptation to contend with mutations.
Or perhaps it’s some other explanation we don’t even know enough to imagine now.
Bodonids are not the only microbes that force us to reevaluate the fundamentals.
Microbes are constantly showing us different ways to do the basics,
and inspiring new techniques in the process.
Tools like CRISPR are rooted in this kind of reevaluation, this expansion and complication
of our dogmas.
This is usually the point in an episode where I want to end by sighing and saying,
“All that, and this organism is just living its life!
It doesn’t know!”
Because that is sometimes what it feels like.
Hundreds of words about this invisible process buried deep in this funny, flagellated creature
that doesn’t know what we’re even talking about.
It doesn’t know why we’ve spent all this time looking at it and studying it.
And even if it did, would it really care?
It has a whole life to live, a life that will continue long after I’m done talking about
RNA editing.
And we will never get to know what the entirety of that life is.
Only that it involves chainmail made of DNA, circles of information linked together to
produce questions we will chase forever.
Thank you for coming on this journey with us as we explore the unseen world that surrounds us.
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