Model Organisms |
This web page was produced as an assignment for Genetics 564, an undergraduate capstone course at UW-Madison.
What are model organisms?
A model organism is a species that has been widely studied, usually because it is easy to maintain and breed in a laboratory setting and has particular experimental advantages. They are non-human species that are used in the laboratory to help scientists understand biological processes [1].
Why are model organisms useful for genetic research? [1]
- Many model organisms can breed in large numbers.
- Some have a very short generation time, which is the time between being born and being able to reproduce, so several generations can be followed at once.
- Mutants allow scientists to study certain characteristics or diseases. These are model organisms that have undergone a change or mutation? in their DNA? that may result in a change in a certain characteristic.
- Some model organisms have similar genes or similar-sized genomes to humans.
Commonly Used Model Organisms:
Yeast (Saccharomyces cerevisiae) [2]
Yeast is cheap and easy to use in a laboratory as it just requires a simple nutrient broth to grow. It's genome has been fully sequenced and it divides rapidly. Another advantage that makes yeast, such as S. cerevisiae, useful as a model organism is that it has a small genome, but it can still carry out all of the most complex processes needed for it to function and survive. It has also been very useful in understanding complex processes such as the eukaryotic cell cycle. |
Nematode worm (Caenorhabditis elegans) [2]
This was the first multi-cellular organism to have their genome fully sequenced. They are small and transparent organisms. They have also provided scientists with useful information about development. These organisms can be useful in trying to understand ageing and cancer. They also can survive indefinitely when placed in a freezer and have a short lifespan. All of these factors make them a very cheap and useful model organism. |
Western clawed frog (Xenopus tropicalis) [2]
Frogs have large embryos that are relatively easy to manipulate and are more similar to humans than Drosophila and Zebrafish. They are also able to regenerate body parts. They have been used to show how signals from one tissue diffusing to another can direct development. It is used in research regarding embryonic development and birth defects. Its eggs are very easy to manipulate and the females are able to lay eggs at any time in the year. |
Mouse (Mus musculus) [2]
There are very few differences between mice and humans anatomically or in terms of cell structure. This makes them more reliable to use them as a model organism when looking to make conclusions about humans. Mice are chosen as the model mammal organism as they are small and easy to keep. They also have a fully sequenced genome. Most mutations in a mouse gene correspond to a similar mutation is a human orthologue, and often a similar phenotype may be expressed. This enables scientists to understand a great deal more about certain genetic diseases that occur in the human population. However, they are expensive to keep in a laboratory compared to other model organisms. |
Fruit fly (Drosophila melanogaster) [2]
Unlike yeast, Drosophila is a multicellular organism, just like humans, and therefore may be more useful in certain studies. It has a giant chromosome that is visible in some of its cells. Drosophila has a very fast maturation rate and a short lifespan. They have had their genome fully sequenced and they are cheap to breed. Drosophila has played an important role in understanding vertebrate development. |
Which model organism should be used to study NRXN3?
The FlyBase database was useful in obtaining phenotypic information of the gene, NRXN3. It appears that Drosophila shares phenotypes with humans that could be useful for studying the effects of substances on the body such as alcohol.
How Alcohol Affects HumansAlcohol affects the human body in many ways. This includes pancreatitis, liver disease, gastritis, stomach ulcers, and esophageal ulcers. More importantly, alcohol affects the human brain in the form of cognitive impairment, memory loss, and lack of motor coordination [3].
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How Alcohol Affects Drosophila
Wildtype - Coordinated [1] |
Mutant - Uncoordinated [2] |
Drosophila melanogaster, commonly known as fruit flies, tend to dine on rotting or fermenting fruit which release significant amounts of alcohol (up to 4%). In the wild, fruit flies are resistant to the toxic effects of alcohol, but in the lab mutant strains of flies have been created that are alcohol sensitive. When sensitive flies are exposed to alcohol vapors (alcohol in gas form), their behavior can be remarkably similar to some humans! The flies become hyperactive, uncoordinated, sedated, and pass out [4]. The FlyBase database reveals that there are 3419 records of locomotor behavior defective phenotypes regarding NRXN3 in flies. This breaks down into three specific phenotypes that are commonly observed in flies during brain research. These phenotypes include jump response defective phenotype (16 records), locomotor rhythm defective phenotype (765 records), and the uncoordinated phenotype (431 records) [5].
Conclusion
Drosophila melanogaster would be a good model organism to use in studying the NRXNR gene due to the many reasons outlined above. They are cheap to breed and easy to maintain in a lab setting. They have a short lifespan and fast maturation rate. Their genome is fully sequenced and are extensively used in brain research. They exhibit similar behavioral phenotypes to humans (uncoordination) when exposed to alcohol vapors. Therefore, it can be deduced that irregular function of NRXN3 should induce such a phenotype and indicate improper synaptic function/decreased synaptic count, and alcohol dependence.
References
[1] https://www.yourgenome.org/facts/what-are-model-organisms
[2] Model organism. (2017, December 6). Retrieved April 7, 2018, from https://teaching.ncl.ac.uk/bms/wiki/index.php/Model_organism#cite_note-4
[3] Ahmadiantehrani, S., Warnault, V., Legastelois, R., & Ron, D. (2014). From Signaling Pathways to Behavior. Neurobiology of Alcohol Dependence, 155-171. doi:10.1016/b978-0-12-405941-2.00009-2
[4] G. (n.d.). ModENCODE. Retrieved from http://modencode.sciencemag.org/drosophila/alcoholism/
[5] FlyBase. (n.d.). Retrieved April 9, 2018, from http://flybase.org/cgi-bin/cvreport.pl?id=FBcv:0000414
Images
Header: https://www.hannahliart.com/#/new-gallery-2/
https://upload.wikimedia.org/wikipedia/commons/thumb/9/95/Saccharomyces_cerevisiae_SEM.jpg/1200px-Saccharomyces_cerevisiae_SEM.jpg
http://macaulay.cuny.edu/eportfolios/wormsandlearning/files/2016/05/From-I.-Chin-Sang.png
https://upload.wikimedia.org/wikipedia/commons/thumb/b/b4/Xenopus_laevis_02.jpg/1200px-Xenopus_laevis_02.jpg
https://prestaservmt.com.br/wp-content/uploads/2018/03/mus-musculus.jpg
http://www.zebrafishfilm.org/uploads/1/1/3/5/113588191/small-zebrafish-from-shutterstock_orig.png
https://www.yourgenome.org/sites/default/files/styles/banner/public/banners/stories/fruit-flies-in-the-laboratory/single-fruit-fly-drosophila-melanogaster-on-white-background-cropped.jpg?itok=KeimCcd-
Videos
[1] https://www.youtube.com/watch?v=FVI9FSPnTWk
[2] https://www.youtube.com/watch?v=3D_ZU248roY
[1] https://www.yourgenome.org/facts/what-are-model-organisms
[2] Model organism. (2017, December 6). Retrieved April 7, 2018, from https://teaching.ncl.ac.uk/bms/wiki/index.php/Model_organism#cite_note-4
[3] Ahmadiantehrani, S., Warnault, V., Legastelois, R., & Ron, D. (2014). From Signaling Pathways to Behavior. Neurobiology of Alcohol Dependence, 155-171. doi:10.1016/b978-0-12-405941-2.00009-2
[4] G. (n.d.). ModENCODE. Retrieved from http://modencode.sciencemag.org/drosophila/alcoholism/
[5] FlyBase. (n.d.). Retrieved April 9, 2018, from http://flybase.org/cgi-bin/cvreport.pl?id=FBcv:0000414
Images
Header: https://www.hannahliart.com/#/new-gallery-2/
https://upload.wikimedia.org/wikipedia/commons/thumb/9/95/Saccharomyces_cerevisiae_SEM.jpg/1200px-Saccharomyces_cerevisiae_SEM.jpg
http://macaulay.cuny.edu/eportfolios/wormsandlearning/files/2016/05/From-I.-Chin-Sang.png
https://upload.wikimedia.org/wikipedia/commons/thumb/b/b4/Xenopus_laevis_02.jpg/1200px-Xenopus_laevis_02.jpg
https://prestaservmt.com.br/wp-content/uploads/2018/03/mus-musculus.jpg
http://www.zebrafishfilm.org/uploads/1/1/3/5/113588191/small-zebrafish-from-shutterstock_orig.png
https://www.yourgenome.org/sites/default/files/styles/banner/public/banners/stories/fruit-flies-in-the-laboratory/single-fruit-fly-drosophila-melanogaster-on-white-background-cropped.jpg?itok=KeimCcd-
Videos
[1] https://www.youtube.com/watch?v=FVI9FSPnTWk
[2] https://www.youtube.com/watch?v=3D_ZU248roY