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  • Imagine that day by day,

  • your field of vision becomes slightly smaller,

  • narrowing or dimming

  • until eventually you go completely blind.

  • We tend to think of blindness as something you're born with,

  • but in fact, with many diseases like Retinitis pigmentosa

  • and Usher syndrome,

  • blindness can start developing when you're a kid,

  • or even when you're an adult.

  • Both of these rare genetic diseases affect the retina,

  • the screen at the back of the eye that detects light and helps us see.

  • Now imagine if the eye could regenerate itself

  • so that a blind person could see again.

  • To understand if that's possible, we need to grasp how the retina works

  • and what it has to do with a multitalented creature

  • named the zebrafish.

  • The human retina is made of different layers of cells,

  • with special neurons that live in the back of the eye

  • called rod and cone photoreceptors.

  • Photoreceptors convert the light coming into your eye

  • into signals that the brain uses to generate vision.

  • People who have Usher syndrome and retinitis pigmentosa

  • experience a steady loss of these photoreceptors

  • until finally that screen in the eye can no longer detect light

  • nor broadcast signals to the brain.

  • Unlike most of your body's cells, photoreceptors don't divide and multiply.

  • We're born with all the photoreceptors we'll ever have,

  • which is why babies have such big eyes for their faces

  • and part of why they're so cute.

  • But that isn't the case for all animals.

  • Take the zebrafish, a master regenerator.

  • It can grow back its skin, bones, heart and retina after they've been damaged.

  • If photoreceptors in the zebrafish retina are removed or killed by toxins,

  • they just regenerate and rewire themselves to the brain to restore sight.

  • Scientists have been investigating this superpower

  • because zebrafish retina are also structured very much like human retina.

  • Scientists can even mimic the effects of disorders like Usher syndrome

  • or retinitis pigmentosa on the zebrafish eye.

  • This allows them to see how zebrafish go about repairing their retinas

  • so they might use similar tactics to fix human eyes one day, too.

  • So what's behind the zebrafish's superpower?

  • The main players are sets of long cells that stretch across the retina

  • calledller glia.

  • When the photoreceptors are damaged, these cells transform,

  • taking on a new character.

  • They become less likeller cells and more like stem cells,

  • which can turn into any kind of cell.

  • Then these long cells divide,

  • producing extras that will eventually grow into new photoreceptors,

  • travel to the back of the eye and rewire themselves into the brain.

  • And now some researchers even think they've found the key to how this works

  • with the help of one of two chemicals that create activity in the brain

  • called glutamate and aminoadipate.

  • In mouse eyes,

  • these make theller glia divide and transform into photoreceptors,

  • which then travel to the back of the retina,

  • like they're replenishing a failing army with new soldiers.

  • But remember, none of this has happened in our retinas yet,

  • so the question is how do we trigger this transformation of theller glia

  • in the human eye?

  • How can we fully control this process?

  • How do photoreceptors rewire themselves into the retina?

  • And is it even possible to trigger this in humans?

  • Or has this mechanism been lost over time in evolution?

  • Until we tease apart the origins of this ability,

  • retinal regeneration will remain a mysterious superpower

  • of the common zebrafish.

Imagine that day by day,

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B2 US TED-Ed photoreceptors retina eye regenerate usher

【TED-Ed】Could a blind eye regenerate? - David Davila

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    稲葉白兎 posted on 2015/06/25
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