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In the last few years, we’ve seen scientists make big advancements
with organoids — these are clumps of tissues made in the lab
that mimic the biology of a full-blown organ.
While it’s still a relatively new technique, scientists have
been able to make organoids of everything from intestines
to lungs and even brain tissue.
These mini-organs in a dish are models that help us understand
the functions of those organs without having to have the full version at hand.
Recently, Dutch researchers publishing in the journal Cell Stem Cell
figured out a way to make organoids that resemble tear glands.
And weirdly enough, they can actually cry.
The scientists started by collecting stem cells from the tear glands
of mice and from human participants, and then they grew them
with some chemicals known to be involved in eye development.
Once they had organoids to work with,
the next challenge was getting them to cry.
Unfortunately, cells in a dish don’t quite have the emotional response
to like, Titanic, that we do, so you can’t just show them
a movie and hope for the best.
And so, instead of making an organoid read The Fault In Our Stars,
the researchers exposed the tissue to one of the neurotransmitters
that causes humans to get all misty eyed — noradrenaline.
Sure enough, when the organoids were exposed to the neurotransmitter,
they swelled up with fluid.
But the researchers weren’t done there.
They took some of the stem cells made from mice, and then deleted
a gene called Pax6, which is involved in eye development.
Then they raised those cells into tear gland organoids
lacking that important gene.
These organoids not only grew more slowly, but weren’t able
to produce tears, which means this gene was crucial
for proper tear gland development.
Understanding how these organoids produce tears should help human
patients with conditions like Sjögren’s syndrome,
an autoimmune disease that leaves the sufferer with dry eyes and mouth.
Sjögren's patients tend to have less of the protein made by
the Pax6 gene, so this research model should help us study
how that affects tear production.
These model tear glands aren’t all the way there yet, though.
They’re made of one type of cell: ductal cells.
But experiments in mice told the team that they were missing
at least one key cell type.
So their future work will focus on making more complete models.
That means we're still a long time away
from fully lab-grown tear gland transplants.
But the research group is hopeful that their work will lead
to a better lab model, so that other researchers
can study tear-related diseases more accurately.
In more eye-related news, an article published last week in
Science Advances suggests that the genetics of eye color
are way more complex than we imagined.
In the paper, an international team of scientists analyzed
the genomes of almost two hundred thousand people and identified
fifty new genes that are involved in eye color.
And that’s a big departure from how you may have learned about
the genetics of eye color in school.
See, in the past we thought of eye color as a Mendelian trait.
That means a trait governed by just one or a few genes,
so it’s easy to predict how that trait will be passed on.
If you knew the eye colors of both parents, then you could predict
the eye color of the offspring, since the gene for brown eyes
was thought to be dominant over the gene for blue eyes.
But eye color doesn’t just break down into brown, green, or blue.
There’s a lot more variation than one gene can account for
-- like shades of brown.
In fact, previous research had found around a dozen genes linked to eye color.
Eye color is still inherited from your parents, but more than one gene is involved.
So in this recent study, the researchers did something called
a genome-wide association study — which is a way to capture
the influence of a large number of genes across a large population.
Then they asked participants to self-categorize their eye color,
and if they had brown eyes, to include exactly which shade of brown.
Now, the vast majority of participants had European ancestry,
so they also recruited about sixteen hundred people
with Asian ancestry, and did the same genetic analysis.
All in all, the analysis found fifty genes that influenced which eye
color the participant had -- in addition to the ones already known.
Only eight of these fifty genes had already been associated
with some kind of pigmented trait, like hair or skin color.
So even though variations in these traits are frequently seen together,
like blonde hair with blue eyes, those traits are influenced by different genes.
The researchers also found that the same genes influence eye color
in people of both European and Asian ancestry.
Meaning the same genes that influence blue or brown eye color
also help determine individual shades of brown.
So it’s not a simple matter of brown being dominant over blue.
Now, there are a few different diseases that involve eye pigmentation
— conditions like albinism or pigmentary glaucoma.
The research group hopes their findings will help shine some light
on how those work and how to treat them.
But it also shows us that the simplest things aren’t always
as simple as we thought -- and there’s always more to understand
about the world and ourselves.
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There’s a course on computational biology, which among other things,
will help you learn more about the math behind the genome-wide studies
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So thanks!
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