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  • When you look at a zebrafish, you probably just see a cute, tiny fish that's smaller

  • than your pinky finger.

  • But this little fish is so much more than that.

  • You're looking at an amazing scientific tool that has led to some major discoveries.

  • Zebrafish have been used since the 1970s to study the development of vertebrates, and

  • more recently, they've been helping scientists learn more about human diseases and maybe

  • even develop some potential treatments.

  • So why the zebrafish?

  • Well, like all fish, their genomes are similar to the human genome, mainly because we share

  • a common ancestor.

  • They have over 26,000 protein-coding genes, and about 70% of those genes are related to

  • similar genes in humans.

  • Since zebrafish have been studied so much, we know that around 80% of the disease-causing

  • genes that have been identified in humans have at least one related gene in zebrafish.

  • By studying what these genes do in zebrafish, scientists can learn more about what they

  • do in humans.

  • And there are other reasons researchers specifically study zebrafish:

  • They're cheap to maintain, and the females can spawn around 200 to 300 eggs in a single

  • week, which makes for a lot of new test subjects.

  • More importantly, zebrafish embryos and larvae are transparent and develop really quickly.

  • There's even a genetically-engineered strain of zebrafish that's transparent through

  • its whole life.

  • That transparency allows researchers to see exactly what's going on inside the fish's

  • body, and watch biological processeslike how cancers develop.

  • That said, zebrafish still aren't the perfect model for human diseasefor one thing,

  • they don't have lungs or mammary glands.

  • Plus, a lot of their genome is made up of duplicate genes.

  • Some of those gene copies might have mutated and developed functions that weren't there

  • in the ancestor's genewhich would make them different from the human versions.

  • Even so, zebrafish have been able to help scientists learn about a lot of different

  • diseases -- like melanoma, the most dangerous type of skin cancer.

  • Cancer develops because of mutations in specific genes that affect how cells multiply and die.

  • And the most common mutation related to the melanoma is called BRAF(V600E).

  • Zebrafish that carry this mutation, and also lack a tumor-suppressing gene, make good models

  • for the disease.

  • So researchers can study how cancer develops in fish with the BRAF mutation, and use them

  • to test treatments.

  • They've also used zebrafish to find other melanoma-causing genes.

  • See, sometimes, the BRAF mutation just causes benign moles instead of melanoma.

  • BRAF might start the process, but another gene has to cooperate to actually cause the

  • melanoma.

  • The question was how to find that gene.

  • The researchers used human melanoma samples to look for duplicated genes that might cause

  • cancer along a certain section of a human chromosome.

  • The duplicated genes they found were then inserted into the genomes of zebrafish with

  • the BRAF mutation.

  • And only one gene, called SETDB1, was found to accelerate melanoma formation in the zebrafish.

  • This discovery might lead to the creation of new cancer therapies that target SETDB1.

  • Zebrafish research might also be able to help with stem cell transplants.

  • And the reason for that has to do with a compound called prostaglandin E2.

  • In a study, researchers discovered that when certain chemicals were used to enhance prostaglandin

  • E2 synthesis, the amount of hematopoietic, or blood, stem cells in the zebrafish increased.

  • So, extra prostaglandin E2 might be able to help treat someone who's getting a blood

  • stem cell transplant, like a leukemia patient or someone with a blood or immune system disorder.

  • Which is great news!

  • This discovery eventually led to the creation of a drug called ProHema that's supposed

  • to improve the success of hematopoietic stem cell transplants using blood from umbilical

  • cords.

  • Between 2014 and 2015, it went through stage II clinical trials where it was tested on

  • patients to see how well it works.

  • And the results are pretty promising.

  • In patients who were taking ProHema, stem cell transplants seemed to start working earlier

  • than the control group.

  • So, ProHema might help improve the effectiveness of these stem cell transplants, but it still

  • needs to be tested more.

  • A specific trait of zebrafish might also help scientists with regenerating human tissue.

  • If a zebrafish heart gets damaged, it can regenerate.

  • Even if part of the heart is removed, it'll just form a clot at the wound site, which

  • eventually gets replaced with new cardiac muscle.

  • But if part of a human heart gets damaged -- like from a heart attack -- the damaged

  • area generally just turns into scar tissue, which doesn't pump as well as healthy tissue.

  • If you could regenerate healthy cardiac muscle instead, you could avoid that permanent damage.

  • While it's still being studied, it seems like the reason zebrafish can do this and

  • we can't is because the injury activates their cardiac muscle cells, which then regrow

  • the tissue.

  • As scientists learn exactly how that's done, the idea of human tissue regeneration might

  • get closer to becoming a reality.

  • So the zebrafish may be tiny.

  • But it's helping modern medicine in a big way.

  • Thanks for watching this episode of SciShow, which was brought to you by our patrons on

  • Patreon.

  • If you want to help support this show, just go to patreon.com/scishow.

  • And don't forget to go to youtube.com/scishow and subscribe!

When you look at a zebrafish, you probably just see a cute, tiny fish that's smaller

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