Neurons at work: Research provides a clearer view of 'alternative splicing'

August 12, 2014 by Peter Reuell, Harvard University
Credit: Rose Lincoln/Harvard Staff Photographer Through their research on “alternative splicing,” John Calarco (left), a Bauer Fellow at the Faculty of Arts and Sciences Center for Systems Biology, and postdoctoral researcher Adam Norris have a better understanding of how the process works in different neurons. Their findings could also uncover insights on how it can go awry and lead to disorders such as epilepsy.

Film editors play a critical role by helping shape raw footage into a narrative. Part of the challenge is that their work can have a profound impact on the finished product—with just a few cuts in the wrong places, comedy can become tragedy, or vice versa.

A similar process, "," is at work inside the bodies of billions of creatures—including humans. Just as a film editor can change the story with a few cuts, alternative splicing allows cells to stitch genetic information into different formations, enabling a single gene to produce up to thousands of different proteins.

Harvard scientists say they've now been able to observe that process within the nervous system of a living creature.

Using genetic tools to implant genes that produce fluorescent proteins in the DNA of transparent C. elegans worms, John Calarco, a Bauer Fellow at the Faculty of Arts and Sciences Center for Systems Biology, and postdoctoral researcher Adam Norris were able to gather hard evidence that the alternative splicing process frequently works differently in different types of neurons.The study was described in a recent paper in Molecular Cell.

"Splicing is an essential process in gene regulation that happens in most eukaryotic cells, all the time," Calarco said. "It's a fundamental part of how eukaryotic genes produce proteins, but when it goes wrong, it can lead to any number of diseases, including in the nervous system."

On the surface, Calarco said, the splicing process is relatively simple. To manufacture a particular protein, DNA is first transcribed into messenger RNA (mRNA). But while that transcription contains the instructions to code for a protein, it also contains noncoding segments. Once those segments are removed, the remaining must be stitched back together, with different combinations producing different proteins.

Science had long understood how the process generally works. One question that remained was whether closely related cell types frequently used the process to produce distinct proteins from the same .

"We were interested in looking at how splicing might be different in one type of neuron versus a different type of neuron," said Norris. "We didn't know whether that was often going to be true going in, so we were looking for indicators that that might be happening."

What they found was clear—different cells splice the same genes in different ways. The process can be visualized in real time using a fluorescent protein-based approach.

"What we've been able to do is visualize the alternative splicing process in these animals in single neurons," he said. "We engineered fluorescent proteins in such a way that they can provide an indication of how the RNA is being differentially spliced. If a particular coding segment is present, the protein will glow red, and if it's removed, it will glow green."

When Calarco and Norris used the to target two types of motor neurons in the worms, they immediately saw a distinctive fluorescent pattern emerge, meaning the two classes of neurons were splicing mRNAs differently.

In additional experiments that targeted other genes, Calarco and Norris were able to identify unique patterns of splicing, suggesting that the process is different not only among different neuron types, but also among different genes.

"What this suggests is that this process is happening pretty frequently, and is very complex, even in an animal—like C. elegans—that has just 302 neurons," Calarco said. "That's why we believe it has a potentially large impact on understanding our own nervous system, which is immensely more complex."

By better understanding how the works in different neurons, Calarco said, scientists might uncover insights on how it can go awry and lead to disorders such as epilepsy.

Ultimately, alternative splicing appears to play a critical role in allowing organisms to evolve greater complexity without the need for ever-larger genomes.

"There are a finite number of genes in the genome, and changing which of those gets turned on or off gives you a certain level of complexity," Calarco said. "What alternative splicing does is add another layer of complexity, allowing an organism to diversify a cell type even more—we think this contributes a great deal to an organism's ability to diversify its cellular function and cellular architecture."

"We know the human is very complex," said Norris. "I think this is one explanation for how that complexity is encoded. We've got on the order of billions of neurons, but we've only got on the order of thousands of genes. How can you create a complex, billion-neuron network with different capacities for each cell? This gives us one explanation for how an organism can do that."

Explore further: Protein expression gets the heart pumping

Related Stories

Protein expression gets the heart pumping

April 22, 2014
Most people think the development of the heart only happens in the womb, however the days and weeks following birth are full of cellular changes that play a role in the structure and function of the heart. Using mouse models, ...

'Cut-and-paste' gene defect hints at cause of developmental disease

February 10, 2014
Melbourne researchers have made a major step forward in understanding how changes in an essential cellular process, called minor class splicing, may cause a severe developmental disease.

Recommended for you

Brain zaps may help curb tics of Tourette syndrome

January 16, 2018
Electric zaps can help rewire the brains of Tourette syndrome patients, effectively reducing their uncontrollable vocal and motor tics, a new study shows.

A 'touching sight': How babies' brains process touch builds foundations for learning

January 16, 2018
Touch is the first of the five senses to develop, yet scientists know far less about the baby's brain response to touch than to, say, the sight of mom's face, or the sound of her voice.

Researchers identify protein involved in cocaine addiction

January 16, 2018
Mount Sinai researchers have identified a protein produced by the immune system—granulocyte-colony stimulating factor (G-CSF)—that could be responsible for the development of cocaine addiction.

Neuroscientists suggest a model for how we gain volitional control of what we hold in our minds

January 16, 2018
Working memory is a sort of "mental sketchpad" that allows you to accomplish everyday tasks such as calling in your hungry family's takeout order and finding the bathroom you were just told "will be the third door on the ...

Brain imaging predicts language learning in deaf children

January 15, 2018
In a new international collaborative study between The Chinese University of Hong Kong and Ann & Robert H. Lurie Children's Hospital of Chicago, researchers created a machine learning algorithm that uses brain scans to predict ...

Preterm babies may suffer setbacks in auditory brain development, speech

January 15, 2018
Preterm babies born early in the third trimester of pregnancy are likely to experience delays in the development of the auditory cortex, a brain region essential to hearing and understanding sound, a new study reveals. Such ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.