Questions about the genetically engineered mice

Stall Catchers The Science
1

I read that most people who get Alzheimer’s don’t have the Alzheimer’s gene, if that is the case, how do you know that the results that you observe using these genetically engineered mice would be the same results that you would see in human beings who have Alzheimer’s disease?

If it’s possible to genetically engineer mice to develop Alzheimer’s disease, why isn’t it possible to cure the mice of Alzheimer’s disease by turning off the gene that causes Alzheimer’s?

If these genetically engineered mice were to escape the laboratory, and start reproducing with the wild field mouse population, would it be possible for them to spread Alzheimer’s to the wild mouse population?

If a predator, like an owl, were to eat one of these genetically engineered mice, would it be possible for the gene to be passed on to the predator? I know that normally, such transmission, would only be possible with a virus, but I thought I would ask the question anyway because some viruses are just strands of RNA which, I guess can be considered to be at the genetic level, although I don’t know that much about genetics.

2

Hi Mike great questions, I asked the same ones when I joined the lab.

First of all, we don’t know of a single gene encoding Alzheimer’s Disease. Some genes have been identified that increase the likelihood of developing the disease, but there isn’t an “Alzheimer’s gene.” My personal opinion on this matter is that Alzheimer’s Disease isn’t one isolated disease but is rather a kind of umbrella under which lie various pathologies that can lead to the observed symptoms and effects-- which makes sense of the lack of a single gene and the presence of “risk factor genes.”

So we don’t have a single easy gene, but there are many different ways to “model Alzheimer’s Disease,” and these various ways are reflected in different mouse model strains. For example; the stall videos you have seen are from a model that has been engineered to over-produce the human protein that ends up accumulating to form plaques, (a phenomenon that would never occur in mice naturally). Compare that technique to inserting a gene known to increase the chance of humans getting Alzheimer’s, to make a model useful in evaluating the role of that risk factor gene. Either way we are inserting human genes so at the protein/cellular level the results we see end up mapping to what we would see in a human fairly well.

There is always the possibility that the model is somehow different from a human brain but we have to start somewhere :slight_smile: as far as the stall phenomenon, our idea is to push forward clinical trials of drugs already deemed safe by the FDA that could confirm that the stall hypothesis holds true in humans, so that development of an ideal medication can begin and dissemination of the pre-approved and somewhat effective medication can happen in the meantime. StallCatchers will be used in analyzing the videos for this project (some of us are working on explanation videos for this project, keep an eye out for word on that as we may need some input!)

The thing to note is that we are modeling what we see in human brains in the mouse brain, mice would never develop the disease themselves.

All that being said, the induced changes end up being a huge disadvantage to the mouse’s overall fitness (as in capability of reproducing and passing on the gene) and they would not survive in the wild. Also notable is that it takes many generations of mating specific pairs that express specific variants of the genes to actually get a model that displays the target effect, so it is very unlikely that whatever the altered gene is could ever make it into a wild population. As far as the predation question, the answer is no- the only way the gene can propogate is via specific mating within a very controlled environment.

These topics are continually discussed in the scientific community, and with better gene editing technology, it is absolutely imperative that people keep asking these questions and that the scientific community isn’t alone with these decisions. I strongly encourage researching these things and starting conversations (like you do) as much as possible. Every time I talk to people I get a perspective I hadn’t get considered and am again reminded how narrow the biological/chemical perspective can be and how important interdisciplinary discussion will be.

Please point out anything I missed or was unclear on.

3

How one gets phenotypic expression of the gene is one issue that I wasn’t clear on. It would seem that if one inserted the gene into a mouse, how could one be sure that the gene would express itself with the traits that you wanted?

Isn’t it possible that these mice could be bred for many generations, and still not have expression of this gene? Obviously, it must not take many generations of breeding mice in order to produce the desired trait because it seems like you have lots of mice to work with. I guess it helps that mice can reproduce fairly quickly, so you don’t have to wait very long to see whether or not the mice will possess the desired trait. I guess it probably helps that because this gene would never occur naturally in the mice, they have no natural “defense” against it, so you don’t really have the issue of recessive genes to deal with.

Does it take a while for the plaque to build up? In other words, do you have to wait until the mice get old, or does the process of plaque buildup begin almost immediately after the mice are born?

Are images taken at different points during the lifespan of each mouse, or are the mice in a permanent coma after the first imaging, and essentially alive, but brain-dead?

Another thing I’m not clear about are the steps involved in testing the drug that might eliminate stalls. At some point, will you be giving the drug to the mice see what effect it has on them? The answer might seem obvious to you, but I’m still confused about exactly what steps are involved in testing the effectiveness of the drug. Right now, we are looking for stalls, when we find enough stalled blood vessels, what will the next step be in the process?

4

It does indeed take generations of breeding for the expression of the gene. We check (sequence) all mice when they’re born to determine which have “successfully” inherited the inserted genes. The development of these models is a whole field in and of itself, and many labs buy mouse models from big companies to at least start with. Plaque buildup takes a different amount of time for different models, sometimes 6 weeks sometimes 6 months, but the timing is consistent within the model. Check out this site, it will give you an idea of how different models are available, why some are selected for certain projects, etc.
http://www.alzforum.org/research-models

Images are taken at different points in the lifespan, the mice are not at all brain-dead. We surgically implant glass windows into the skull so that mice can be repeatedly imaged. They handle the windows remarkably well and can live normally for a long time after the window is implanted.

We are working on a video series to better explain how StallCatchers is facilitating multiple different projects that tackle the drug development question in different ways, but the one I mentioned above is what you described-- giving the mice a drug that we know is ok when taken by humans (because it has been approved for use in other diseases), and then determining whether the number of stalls in the mice brains has decreased. Comparing the number of stalls in mice treated with a drug vs mice treated with a placebo will confirm or deny the hypothesis that the drug can clear stalls. When we find one of these pre-approved drugs that can clear stalls, we can move on to clinical trials, which will be the first data on whether the phenomenon exists in humans as it does in mice (I don’t think anyone would want a glass window implanted in their head, and our brains are much harder to image because of their size). Please note that this project is happening in parallel to others that seek to better understand what causes the stalls in the first place, which is a more thorough way of approaching the issue but one that needs the confirmation of the stall phenomenon in humans to continue fruitfully. In short, comparing the number of stalls in the brains of treated vs untreated mice tells us whether the medication can clear stalls. The question “does one group of mice have fewer stalls than the other” is at the core of all of our projects, and why StallCatchers exists!

5

Do the mice have any kind of enrichment activity for them to do while they’re waiting to be imaged? Do they have a wheel to run on, or toys to play with? On the face of it, it might seem like a silly question, but exercise has been shown to improve blood flow in the brain, and having toys to play with, I think has been shown to increase the branching of dendrites, or maybe its the growth of axons. I can’t quite remember at the moment. I can see that that might be one research question. For example, do mice who get several hours of exercise a night, have fewer stalled blood vessels than those who get no exercise?

Also, I guess having some enrichment activities would give the mice some quality of life. It must be kind of boring being a lab mouse, if they don’t have anything to keep them occupied. Although I guess enrichment activities for the mice are not exactly a priority in this particular instance.

1 Like
6

Hi @MikeLandau!

I am hoping @lvinarcsik will also answer this in more depth. But speaking of mice & the things they love to do - last time we were visiting the Schaffer-Nishimura Lab, Chris & Nozomi showed us some of the equipment they use for imaging the brain of the mice. And this cool device was constructed precisely to allow the mice to do what they love (running!) while keeping still, so the images can be taken:

18646100_659914850882679_2371262426352975872_n.jpg640×640 58.7 KB

The mouse is placed on this surface (with head fixed), the device floats and the mouse can keep walking therefore staying as comfortable as possible :slight_smile: pretty cool, ha!

7

That is cool! I’m glad to know that they take the comfort of the mice into consideration. I guess they figure that a happy mouse is a cooperative mouse. This does however raise another question. I thought that the mice were anesthetized during the filming. Clearly, if this device is being used, the mouse has to be awake while he or she is running. Does that mean that some of the mice are anesthetized during filming, while others are using this running device while the procedure is being done?

If some of the mice are unconscious during the filming, and others are using this running device during the filming, that would definitely explain the differences that we see, in heart rate, and blood flow from one movie to the next. Under what circumstances is this running device used, instead of the mouse being anesthetized during the filming?

Another thing I’ve been wondering is, why are the visual presentations that we are looking at in the stall catchers game referred to as movies, instead of videos? Is it just because movies sound more fun than videos, or is there some other reason?

One other question, when you say the mouse is floating, I’m not exactly sure what you mean by that. Do you mean that he’s floating in water somehow? Another photograph showing more clearly what’s going on would be helpful.

Thank you very much to everyone for the great explanations!

8

Does that mean that some of the mice are anesthetized during filming, while others are using this running device while the procedure is being done?
Under what circumstances is this running device used, instead of the mouse being anesthetized during the filming?

Hi there, I think this device has caused some confusion- this is not used in most imaging sessions. It was used to determine whether the mice had differences in stalling and bloodflow when under anesthesia, we found there is no difference. This was a key question to ask in the beginning when we were designing experiments to answer our questions. While we could theoretically use this device to awake-image every mouse, we get higher quality videos with mice under anesthesia because there is less motion to control for. I also think the mice might prefer sleeping to the stress of being in a strange new room with strange sounds and lights.

Do the mice have any kind of enrichment activity for them to do while they’re waiting to be imaged? Do they have a wheel to run on, or toys to play with?
For example, do mice who get several hours of exercise a night, have fewer stalled blood vessels than those who get no exercise?

Yes, the mice have some objects to interact with and we avoid single housing as much as possible so that they have siblings to keep them company. Our mice are housed in a facility adjacent to the lab and there is a whole staff in place to keep their cages clean and their food and water full. Good question about the exercise, could very well be an upcoming experiment but we currently don’t have someone with enough time to do this experiment (it would require many hours every day just to facilitate exercise evenly).

Another thing I’ve been wondering is, why are the visual presentations that we are looking at in the stall catchers game referred to as movies, instead of videos? Is it just because movies sound more fun than videos, or is there some other reason?

I’m not sure, @pietro might have thoughts?

9

Oops missed this one-- the mouse is walking on a floating ball that keeps moving every time the mouse moves its feet, the ball protrudes out of the water so the mouse is walking on a solid surface.

10

Can the mouse see the water, or just the ball? If the mouse can see the water, then I can imagine that it might be very stressful for the mouse because it might think that if it doesn’t keep running, it’s going to fall into the water. One way to produce stress in mice is to make them swim in water. As I understand it, they don’t particularly like to swim.

11

The mice can’t see the water because their heads are being held stationary for imaging (maybe more stressful!). While the lab tries to minimize stressing the animals there are certainly inherent discomforts that are hard to avoid- one of the many criticisms of using animal models. If you’re interested in Cornell’s policies and restrictions check out here: Home | Cornell Research Services

12

That does sound stressful. How do you get the head of the mouse into the device? It would seem like he or she might be struggling quite a bit. I hope they get some kind of a treat or reward after that experience. I guess though if the mouse experienced the situation a few times, eventually it might get used to it.

Do you use both males and females in the experiments? I would assume that you would have to use both males and females, or otherwise sex might become a variable that would have some influence on the results. Does one sex have more stalled blood vessels than another, or do males and females have about the same number of stalled blood vessels?

13

We do use both sexes, and have not noticed a difference in number of stalls so far. You are right that a good experimental design needs to account for the possibility that differences in sex (and age, environment, food, etc etc) may influence data. Rest assured we take confounding variables into account.