The Incredibly Useful Zebrafish: Their Application in the Science of Sleep

Zebrafish are beautiful little creatures, but they might also be helping us better understand the science of sleep.

Zebrafish are incredible creatures. They are a common occurrence in many aquariums around the world, and they are also pretty handy for scientific research.

One area they are being used to make significant breakthroughs is in sleep studies. In a recent study, researchers might be a step closer to understanding why we sleep.

It would also open the door to better treatments for sleep deprivation and other sleep-related disorders. 

RELATED: THIS STUDY OF MUTANT ZEBRAFISH COULD HELP TREAT AUTISM IN THE FUTURE

The role of zebrafish in sleep studies

Zebrafish are common test animals for scientific research. From creating new drugs to studying ways to treat autism, they have specific characteristics that make them ideal for this. 

Some recent studies have used them to help us understand the mysteries behind sleep. For example, researchers were able to identify sleep patterns in the brains of Zebrafish in a recent study published in the Journal Nature.

By using a combination of genetic engineering and a specially developed technique to scan the entire zebrafish, the team made some interesting findings. The gene they inserted was expressed as fluorescent proteins that fluoresce when calcium in the cell increased. 

An increase in calcium in this manner is often used as a proxy for increased physiological activity. So the more a muscle or eye-lid, or neurons in the brain fire, the more it "flashes."

By focusing on the brain, the researchers were able to record cellular activity in real-time. 

This might not sound too remarkable, but it turns out these patterns are incredibly similar to those of human beings.

The researchers, according to National Geographic, believe these "similar sleep patterns in both fish and mammals may offer clues about the evolution of sleep in our common ancestors, which could, in turn, help us better understand the biological function of nodding off."

zebrafish and sleep studies
Source: kieferpix/iStock

This could bring the scientific community a step closer to understanding why we even sleep at all. To date, there really isn't a consensus on this seemingly simple question.

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The previously-mentioned study seems to indicate that sleep, especially REM-stages, must have had a very early evolutionary benefit, evolving more than 450 million years ago. 

zebrafish sleep deprivation
Source: Quinn Dombrowski/Flickr

But its not just interesting from an evolutionary perspective. This kind of research involving zebrafish could pave the way for developing future drugs to help treat what some have called a growing epidemic of sleep deprivation in many countries around the world. 

What is special about the zebrafish?

Zebrafish (or Danio rerio) are not only strikingly beautiful creatures, but they are also pretty useful for scientific research. They belong to the minnow family of fish (Cyprinidae), are a common sight in many an aquarium in both homes and, it turns out, in laboratories.

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For humans, the zebrafish has little economic value for food or as feed for other animals, but they are very popular in the aquarium trade. These tiny tropical freshwater fish have specific qualities that make them ideal for various reasons. 

In their embryonic developmental stage, zebrafish happen to be transparent. This makes them great for scientists to be able to peer into their inner working with relative ease.

Zebrafish's embryos also develop very rapidly and, as it turns out, about 70 percent of our genes have a zebrafish counterpart. From fertilized egg to hatching as a free-swimming larva takes a little under three days, and the fish grow to maturity in around three months. 

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zebrafish and sleep studies
Source: Oregan State University/Flickr

So, if researchers make changes in the fish's basal genome, they can see the effects of their work very quickly. Changes can be analyzed and reviewed in rapid time. 

Because of this, zebrafish are often one of the most common animals that are used as test subjects or model organisms for developing therapies, for various human medical conditions. They have also become very popular for aiding scientists in the development of some treatments for brain disorders.

Interestingly, zebrafish are one of the few fish species to have actually been flown into space too. Onboard the ISS, zebrafish were used to examine the effects of gravity on muscle maintenance in animals. 

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What are zebrafish used for and what are the benefits?

As we have already mentioned, zebrafish are used for many scientific experiments. In fact, they have been used for this purpose since the 1960s and 1970s.

To date, zebrafish have been used for various research projects including, but not limited to, the following: 

  • The study of cloning
  • Developmental biology

  • Oncology

  • Toxicology

  • Reproductive studies

  • Teratology

  • Genetics

  • Neurobiology

  • Environmental sciences

  • Stem cell research

  • Regenerative medicine

  • Muscular dystrophies

  • Evolutionary theory

What are the advantages of using zebrafish for research?

Their main benefits for research are as follows (courtesy of yourgenome.org): 

  • The zebrafish is small and robust.

  • They are cheaper to maintain than mice.

  • Break of daylight triggers mating in zebrafish (other fish only lay eggs in the dark).

  • Zebrafish can produce hundreds of offspring at weekly intervals providing scientists with an ample supply of embryos to study.

  • They grow at an extremely fast rate, developing as much in a day as a human embryo develops in one month.

  • Zebrafish embryos are nearly transparent, which allows researchers to easily examine the development of internal structures. Every blood vessel in a living zebrafish embryo can be seen using just a low-power microscope.

  • As zebrafish eggs are fertilized and develop outside the mother’s body, it is an ideal model organism for studying early development.

  • Zebrafish have a similar genetic structure to humans. They share 70 percent of their genes with us.

  • 84 percent of genes known to be associated with disease in humans have a zebrafish counterpart. 

  • As a vertebrate, the zebrafish has the same major organs and tissues as humans. Their muscle, blood, kidney, and eyes share many features with human systems.

  • Zebrafish have the unique ability to repair heart muscle. For example, if part of their heart is removed, they can grow it back in a matter of weeks. Scientists are working to find out the specific factors involved in this process to see if this will help them to develop ways of repairing the heart in humans with heart failure, or for those who have suffered heart attacks.

  • The zebrafish genome has been fully sequenced to a very high quality. This has enabled scientists to create mutations in more than 14,000 genes to study their functions.

How much DNA do humans share with Zebrafish?

We have quite a lot in common with zebrafish, as mentioned before. According to various sources, zebrafish actually share around 70 percent of their DNA with humans. Not only that, 84 percent of genes in the human genome known to be associated with diseases have counterparts in the zebrafish genome. This makes them ideal test subjects for the development of gene therapies and pharmaceuticals. 

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Zebrafish, like humans, have also had their genomes fully sequenced. Which is handy. 

This makes them very useful in research projects in which genes are altered and the results analyzed. A great metaphor for this would be removing one piece of a car and seeing what happens: 

"For example, when a car's steering wheel is removed it may only go in one direction," stated Keith Cheng of Penn State University in a human genome study of zebrafish.

"Since it is unethical to modify random genes in humans, we use model organisms in which the function of one gene is 'knocked down' or 'knocked out.' As a result, we can create mutations in any gene. Researchers can watch the result in mutant embryos, sometimes into adult life stages." he added.

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