Optogenetics and Its Clinical Applications

Recently, research in neurotechnology took up this challenge and came out with some new inventions that could solve many scientific puzzles. Optogenetics is one of them!

Optogenetics deals with a toolset of genetically encoded molecules, opsins that, when targeted to specific neurons within the brain, control the activity of those neurons with light.

Opsins

Opsins are a group of proteins that play a role in the molecular basis of different forms of light- sensing systems including vision, circadian rhythms, phototaxis and photosynthesis.

Opsins go by the name of "rhodopsins", when they are expressed in the rods of retinal layer of the eye.

There are two types of opsins, Type 1 and Type 2, based on their structure and function. Research indicates that these two types of opsins evolved separately and then converged during the process of evolution.

Type I opsins are present in bacteria and algae are referred to as bacteriorhodopsin,  channelrhodopsin and halorhodopsin. They take part in phototaxis or photosynthesis.

Type II opsins are present in eumetazoans (animals excluding sponges) and carry out various functions such as circadian rhythm, pupil constriction and photoisomerization or recycling the non-protein component, the chromophore.

Type II opsins are present in a wide range of simple to complex animals; therefore they are believed to have originated from a common ancestor that existed about 600 million years ago.

Despite their similar functions, Type I and II opsins have evolved independently.
The story of opsin is that of convergence and also of predictability in evolution.

Recent Research

Since the 1970s, opsins have been the subject of several studies due to their mind-blowing biophysical properties, and also for the valuable information that they provide into how various forms of life make use of light as an energy source or sensory cue.

The birth of optogenetics offers a number of interesting insights into the array of factors that started neurotechnological innovation.

Opsins are molecules with seven helical domains. These molecules have the ability to span the lipid membranes of cells in which they are genetically expressed and respond to light by transporting ions across the cell membranes.

Opsin found in bacteria, the bacteriorhodopsin, had successfully been expressed in eukaryotic cell membranes, such as those present in yeast cells and frog oocyte.

Many laboratories are discovering new opsins with improved properties such as better light and color sensitivities and ionic functions.

Viruses harboring genes that code for opsins are popular experimental tools. These viruses achieve specificity by restraining their expression to certain types of neurons.

These optogenetic tools are increasingly being used in famous labs the world over to study to study the role of neurons in information processing and behavior in various types of organisms such as C. elegans (earthworm), Drosophila, zebrafish, mouse, rat, and other forms of primates.

Various different light sources such as conventional mercury, xenon lamps, light-emitting diodes, scanning lasers, femtosecond lasers, and other common microscopy equipment suffice for in vitro use.

Guoping Feng, an MIT professor, has started working on first transgenic mice expressing channelrhodopsin ChR2 (found in bacteria) in their neurons. Large numbers of transgenic mice lines are being created to carry out these studies.

In 2009, Ed Boydon, along with Robert Desimone and Ann Graybiel of the MIT, published the first use of ChR-2 in the nonhuman primate brain (rhesus macaque) without causing any untoward events.

All these research has revealed the exciting possibility of the potential use of optical neuron stimulation as a mode for diagnosis and treatment. However a lot more work is required before it can be unquestioningly established.

Source:

F1000 Biology Reports, DOI:10.3410/B3-11 (open access at http://f1000.com/reports/b/3/11).

Source-Medindia