Eye Insights The eyes of fish grow larger throughout their lives because stem cells produce new tissue in the retina, the light-sensitive lining at the back of the eye. Humans and other mammals lack these stem cells, so the retina can neither grow nor be repaired naturally. Studies of zebrafish show that the development of stem cells in the retina is controlled by chemicals from nerve cells nearby. This research may lead to a better understanding of degenerative diseases of the eyes and nervous system in humans and the causes of cancer, which can occur when stem cells go out of control. Pictured is a cross-section of a zebrafish eye. The ring stained green with the dark centre is the lens, with the retina appearing as a semi-circle around it. Stem cells are concentrated in the regions at either end of the red-stained arcs of nerve connecting tissue. Written by Mick Warwicker — Kara Cerveny Zebrafish Research, UCL, London
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Eye Insights

The eyes of fish grow larger throughout their lives because stem cells produce new tissue in the retina, the light-sensitive lining at the back of the eye. Humans and other mammals lack these stem cells, so the retina can neither grow nor be repaired naturally. Studies of zebrafish show that the development of stem cells in the retina is controlled by chemicals from nerve cells nearby. This research may lead to a better understanding of degenerative diseases of the eyes and nervous system in humans and the causes of cancer, which can occur when stem cells go out of control. Pictured is a cross-section of a zebrafish eye. The ring stained green with the dark centre is the lens, with the retina appearing as a semi-circle around it. Stem cells are concentrated in the regions at either end of the red-stained arcs of nerve connecting tissue.

Written by Mick Warwicker

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Source: bpod.mrc.ac.uk

Bright Eyes A growing foetus is sheltered from the outside world, but external conditions may still affect it. Only a tiny amount of light manages to get inside the womb, but new evidence suggests this may be essential to ensure eyes develop correctly. Inside each growing eye, a cup-shaped network of blood vessels forms to supply the early retina with oxygen and nutrients. After birth these vessels are no longer needed, so they slowly break down. The left-hand image shows the pattern of vessels (stained blue) in the eye of a healthy eight-day-old mouse. In genetically engineered mice that lack the light-absorbing protein melanopsin (right-hand image) the vessels fail to break down normally post-birth, persisting as a dense, tangled mess. Exactly the same thing happens if a foetus grows in total darkness. This discovery may help to explain certain eye abnormalities, although the influence of light during human pregnancy is still unknown. Written by Emma Stoye — Sujata Rao Cincinnati Children’s Hospital Medical Center, USA Reprinted by permission from Macmillan Publishers Ltd: Nature Copyright 2013 Published in Nature 2013
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Bright Eyes

A growing foetus is sheltered from the outside world, but external conditions may still affect it. Only a tiny amount of light manages to get inside the womb, but new evidence suggests this may be essential to ensure eyes develop correctly. Inside each growing eye, a cup-shaped network of blood vessels forms to supply the early retina with oxygen and nutrients. After birth these vessels are no longer needed, so they slowly break down. The left-hand image shows the pattern of vessels (stained blue) in the eye of a healthy eight-day-old mouse. In genetically engineered mice that lack the light-absorbing protein melanopsin (right-hand image) the vessels fail to break down normally post-birth, persisting as a dense, tangled mess. Exactly the same thing happens if a foetus grows in total darkness. This discovery may help to explain certain eye abnormalities, although the influence of light during human pregnancy is still unknown.

Written by Emma Stoye

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Source: bpod.mrc.ac.uk

Through New Eyes Our vision relies on a multi-layered structure on the inner surface of the eye, the retina, bearing specialised light-sensitive neurons known as photoreceptors. Progressive degeneration of these cells leads to blindness, as in inherited diseases such as retinitis pigmentosa. While this cannot be reversed, transplanting healthy cells into the eye may provide a solution. Photoreceptor precursor cells are injected into the retina, where they mature into functional light detectors. In mice genetically modified to show symptoms of these diseases, transplants can restore normal responses to light. Pictured are donor cells (stained green), successfully integrating into the host retina (stained blue) of healthy mice (top left corner) and of mouse models of three different genetic diseases causing blindness in humans. Though the extent of integration still depends on the nature and progression of the disease, this technique raises hopes of recovering sight from a range of conditions. Written by Emmanuelle Briolat — Rachael Pearson & Robin Ali University College London Institute of Ophthalmology, UK Published in PNAS 110(1): 354-359
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Through New Eyes

Our vision relies on a multi-layered structure on the inner surface of the eye, the retina, bearing specialised light-sensitive neurons known as photoreceptors. Progressive degeneration of these cells leads to blindness, as in inherited diseases such as retinitis pigmentosa. While this cannot be reversed, transplanting healthy cells into the eye may provide a solution. Photoreceptor precursor cells are injected into the retina, where they mature into functional light detectors. In mice genetically modified to show symptoms of these diseases, transplants can restore normal responses to light. Pictured are donor cells (stained green), successfully integrating into the host retina (stained blue) of healthy mice (top left corner) and of mouse models of three different genetic diseases causing blindness in humans. Though the extent of integration still depends on the nature and progression of the disease, this technique raises hopes of recovering sight from a range of conditions.

Written by Emmanuelle Briolat

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Source: bpod.mrc.ac.uk

Shady Behaviour As our eyes scan this page, the cells in our retinas are firing off messages. It takes them a split-second to convert this picture – of similar cells inside the retina of a zebrafish – into electrical signals bound for the brain. A high-powered microscope was used here to zoom in on a cross-section of the fish’s retina, highlighting the contours of different layers of cells. The sensitive photoreceptors (the layer of larger, bulky cells on the left) gather light from the outside world, converting it into an electrical signal that penetrates deeper into the retinal tissue (the layers of cells on the right). Meanwhile, the black-coloured, inky pigment cells absorb any excess light, protecting the photoreceptors from damage. Our eyes, it appears, have their own internal pair of sunglasses. Written by John Ankers — Rachel Macdonald and Steve Wilson UCL, UK
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Shady Behaviour

As our eyes scan this page, the cells in our retinas are firing off messages. It takes them a split-second to convert this picture – of similar cells inside the retina of a zebrafish – into electrical signals bound for the brain. A high-powered microscope was used here to zoom in on a cross-section of the fish’s retina, highlighting the contours of different layers of cells. The sensitive photoreceptors (the layer of larger, bulky cells on the left) gather light from the outside world, converting it into an electrical signal that penetrates deeper into the retinal tissue (the layers of cells on the right). Meanwhile, the black-coloured, inky pigment cells absorb any excess light, protecting the photoreceptors from damage. Our eyes, it appears, have their own internal pair of sunglasses.

Written by John Ankers

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Source: bpod.mrc.ac.uk

Shape Shifters All 50-100 trillion cells in our body are tiny contortionists that can change shape on the outside by rearranging themselves on the inside. It’s a trick that fascinates scientists, who coax cells into changing shape in laboratory conditions to study how their internal structures move around and reconnect which may hold clues to the cause of certain diseases including cancer. Here, we see a cell taken from a human retina that has been persuaded using a new technique, to change from round to tear-drop shape. The cell, marooned on a repellent surface, has a precision pulse-laser aimed close to it. Intense heat destroys the surface but leaves the cell unharmed and free to spread along the paths etched by the laser beam. Written by Mick Warwicker — Timothée Vignaud Institute of life sciences research and technologies (iRTSV) Reproduced/adapted with permission from Journal of Cell Science Published in Journal of Cell Science
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Shape Shifters

All 50-100 trillion cells in our body are tiny contortionists that can change shape on the outside by rearranging themselves on the inside. It’s a trick that fascinates scientists, who coax cells into changing shape in laboratory conditions to study how their internal structures move around and reconnect which may hold clues to the cause of certain diseases including cancer. Here, we see a cell taken from a human retina that has been persuaded using a new technique, to change from round to tear-drop shape. The cell, marooned on a repellent surface, has a precision pulse-laser aimed close to it. Intense heat destroys the surface but leaves the cell unharmed and free to spread along the paths etched by the laser beam.

Written by Mick Warwicker

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Source: bpod.mrc.ac.uk

Seeing Blind The human eye can distinguish about ten million colours thanks to the light-sensitive lining at the back of our eye. Containing millions of cells, called rods and cones, the retina (pictured flattened out from a mouse eye) absorbs light and transmits this visual information to the brain. Also within this specialised layer are thousands of melanopsin retinal ganglion cells (stained purple) that control our subconscious responses to light, such as the shrinking and expanding of our pupils. Scientists reveal that these cells also provide unexpected amounts of visual information to the brain during conscious vision. In mice completely lacking rods and cones, the contribution of these ganglion cells was enough to prompt responses to light. This discovery may help to solve the mystery of why some people who lose rods and cones as a result of eye disease can still consciously detect the presence of light even when blind. Written by Lux Fatimathas — Robert Lucas, University of Manchester, UK Satchidananda Panda, Salk Institute for Biological Studies, USA Originally published under Creative Commons (CC-BY 2.0) Published in PLoS Biology 8(12): e1000558
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Seeing Blind

The human eye can distinguish about ten million colours thanks to the light-sensitive lining at the back of our eye. Containing millions of cells, called rods and cones, the retina (pictured flattened out from a mouse eye) absorbs light and transmits this visual information to the brain. Also within this specialised layer are thousands of melanopsin retinal ganglion cells (stained purple) that control our subconscious responses to light, such as the shrinking and expanding of our pupils. Scientists reveal that these cells also provide unexpected amounts of visual information to the brain during conscious vision. In mice completely lacking rods and cones, the contribution of these ganglion cells was enough to prompt responses to light. This discovery may help to solve the mystery of why some people who lose rods and cones as a result of eye disease can still consciously detect the presence of light even when blind.

Written by Lux Fatimathas

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Source: bpod.mrc.ac.uk