Chemical signal in zebra fish , which helps it in regenerating retina,to cure blindness
An Indian-origin scientist, along with others have been able to identify a chemical signal in the zebrafish brain, which helps it in regenerating retina, a finding that may help cure blindness in humans.
What is the importance of this discovery?
According to the researchers the discovery raises the possibility that human retinas can be induced to regenerate, naturally repairing damage caused by degenerative retinal diseases and injury, including age-related macular degeneration and retinitis pigmentosa.
“The prevailing belief has been that the regeneration process in fish retinas is triggered by secreted growth factors, but our results indicate that the neurotransmitter GABA might initiate the process instead,” said James Patton, professor at Vanderbilt University in the US, according to PTI.
“All the regeneration models assume that a retina must be seriously damaged before regeneration takes place, but our studies indicate that GABA can induce this process even in undamaged retinas,” said Patton.
Similarity between the structure of the retinas of fish and mammals:
The structure of the retinas of fish and mammals are basically the same. Although the retina is very thin-less than 0.5 millimetres thick, it contains three layers of nerve cells: photoreceptors that detect the light, horizontal cells that integrate the signals from the photoreceptors and ganglion cells that receive the visual information, route it to the brain.
In addition, the retina contains a special type of adult stem cell, called Muller glia, which spans all three layers and provide mechanical support and electrical insulation. In fish retinas, they also play a key role in regeneration.
What happens when regeneration starts?
When regeneration is triggered, the Muller glia dedifferentiate, begin proliferating, and then differentiate into replacements for the damaged nerve cells. Muller glia is also present in mammalian retinas, but they do not regenerate.
Mahesh Rao, a graduate student, got the idea that GABA-normally a fast-acting neurotransmitter best known for its role of calming nervous activity by inhibiting nerve transmission in the brain-might be the trigger for retinal regeneration. He was inspired by the results of a study in the mouse hippocampus which found that GABA was controlling stem cell activity.
Rao along with Patton and assistant professor Dominic Didiano designed a series of experiments with zebrafish, which determined that high concentrations of GABA in the retina keep the Miller glia quiescent and that they begin dedifferentiating and proliferating when GABA concentrations drop.
How did the researchers test their hypothesis?
The scientists tested their hypothesis in two ways:
- Firstly, by blinding zebrafish and injecting them with drugs that stimulate GABA production and
- Secondly, by injecting normal zebrafish with an enzyme that lowers the GABA levels in their eyes.
The research was published in the journal Stem Cell Reports.