Our article today will again aim to understand how we do science. This time, we will study what is named model organisms. These are simply living organisms we use to achieve our studies. Now I know this topic is highly controversial. Therefore, I hope that this article helps to show how essential studies in living organisms, also called in vivo studies, and how much they’ve contributed to overall science. Next week, we will study models that does not involve animal, or in vitro studies, and their differences.

The first question to answer is why are we doing in vivo studies? The simple answer is because we still don’t have any other choice. While science has advanced tremendously, and as we will see next week we have a lot of choice when it comes to study model, none will provide what an animal can. The most obvious reason is drug testing. Let’s say a lab has found a potential drug to treat heart disease. After years of studies without any animal, the lab can confidently say that it works in vitro. However, that does not mean that it will in vivo. Most in vitro models do not have a very long lifespan. What if this drug increases the chances of cancer? The best way of knowing this is testing it on an animal, and see potential side effects. Now, it is illegal to try any medication on animal if no previous intensive studies have been made. We will see later the ethics of animal studies, but one of the staples is animal comfort, thus injecting drugs with no idea of what they may do is not only illegal but also punishable by law. In conclusion, we use animals in this setting to make sure that the drug is safe in humans. But we also use animals to study diseases. None of our in vitro models will be as accurate as in vivo model of diseases. Thanks to these animal, we found countless medications and saved many lives in the process. Now we will go through examples of in vivo models and their uses throughout science [source / source / source / source].

Yeasts and Fruit flies: staples of genetic studies

We start with rather unusual yet essential model organisms: the yeast, specifically the one called Saccharomyces cervisiae. This species was essential to understand how genes and genetic overall works. As a small organisms, its genome (meaning the entirety of their genes) was mapped and understood very quickly. This in turn helped us understand how genes interact with each other, and how their transcription and translation works. Furthermore, yeasts reproduce extremely fast, which allows us to study genetics and development over multiple generations faster than any other organisms. The same can be said fruit flies, specifically Drosophila melanogaster. Fruit flies have the same advantages as yeasts, being fast breeder, cheap, and easy to genetically map, with the added bonus of being anatomically diverse. While the yeast only looks like a blob of cells, flies have distinct features. This is essential because they allow us to understand the relationship between genetic and development. For instance, we can know which gene allows the production of legs, and which one causes eye color. However, both of these organisms also have disadvantages. The main one being that they are genetically quite different from humans. Although we found genes in yeast and flies that were similar or identical in humans, many discoveries are hard to relate to humans. Furthermore, these organisms lack quantifiable behaviours, making it hard for us to link genetics and behaviours [source / source / source].

Frogs: understanding proteins and cells.

Still unusual, a specific type of frog offers unique tools to study the behaviours of cells and proteins. The Xenopus laevis is an African frog that has very interesting eggs, or oocytes. Indeed, one frog makes a huge amount of eggs, with an interesting particularity: each cell in it has a pre-determined role. It means that we know exactly what each cell will do to become a tadpole. This is extremely interesting to study development and cell behaviour. We can know, for instance, how the morphology of a tadpole will change if we slightly move a cell in the oocyte. The usefulness of these oocytes is enhanced by the sturdiness of these cells. Xenopus oocytes can withstand a lot, from injection to rough manipulation, and still yield a viable tadpole. It allows us to inject genes or protein and see what they do to the cell behaviour or the development. Lastly, eggs and be cultured and used for in vitro studies later. But what’s interesting with oocytes is that they allow us to inject several proteins and see how they interact with each other. This allows us to better understand protein behaviour as well [source / source].

Mammals: understanding diseases and complex behaviours

Mammals are amongst the most used animal models in science, and for a good reason. They have complex behaviours and thinking processes, easily comparable to humans. We use many different mammals, but the most common ones are mice, rats, and primates. Studying them as is is an invaluable tool to understand behaviour and relate it to humans. But more interestingly, we can study behaviours and physiology in context of diseases. While similar, there are big differences between rats and mice which will influence your research. Rats are bigger, easier to manipulate, and closer to humans in terms of genetics and behaviours. But they have a big disadvantage: it is hard to genetically manipulate them. Mice on the other hands are very easily manipulated genetically. This allows us to have mice models for many diseases, and we can study the disease and see its effect on our cells. Primates are great to study group behaviours. As they are closest to us, they can tell a lot on how cognition, memory, and complex behaviours work. However it is extremely hard to work with primate, and it’s almost impossible to genetically modify them, although very recently it was done [source / source / source / source].

The ethics of animal care: the 3Rs

Working with animals in Canada is not only difficult but also very regulated, and rightfully so. The Canadian Council on Animal Care (CCAC) set up many rules to follow when scientists use animals, and the basis is known as the 3Rs. First, Replacement forces us to prove why we need animal. Animal studies are last resort, and unless you prove that no in vitro model can do what you want, you will be denied animals. Second, Reduction forces us to optimize animal use. You have to determine how many animals you need per year, and not only does it have to be the smallest number possible, to have more animals than requested is very hard. Lastly, Refinement forces us to place animal comfort above all. No animal should suffer or be stressed for useless reason. Any amount of pain or stress has to be proven useful for the experiment, and animal comfort is ensured while the animal is not used. For example, mice are not kept separately but rather in group (unless the experiment asks for single housing). Similarly, primates have mandatory physical, social, and play time every day. For any more specifics on animal care, the CCAC website is very thorough [source / source / source / source].

In conclusion, I hope that I managed to show how important animal models are for science. I understand how uncomfortable the topic is, but it is important for the public to understand that not only we are treating animals the best we can, but that we have no other choice, as right now they constitute the best model we have to help human society.