Research 101: Cell culture
After only a few months of waiting, I’m proud to present the second installment of Research 101! I started this series with the intent of providing an in-depth look into some of the most common research techniques. I’m hoping that this can help bridge the gap between what the public believes scientists do and what scientists actually do. You can find my last Research 101 here!
Last time I discussed model organisms, which can be a controversial topic depending on who you talk to. A good follow up to this is a non-controversial topic – cell culture!
Cell culture is vital in many different areas of science, mainly (unsurprisingly) biology. It’s a way to disconnect the use of both humans and animals directly by isolating cells in a dish and growing them in an artificial environment. In general, there are no restrictions to the types of experiments that can be done with cell culture, as no actual organisms are harmed through this technique, just individual cells grown independently. There are, of course, certain caveats that must be considered when doing cell culture
experiments, but these are no different than any other science experiments – typically thinking about good controls and good general experimental design.
Before I begin, I want to make the distinction between in vivo and in vitro experiments. In vivo directly translates to ‘in one that is living’. This means in vivo experiments are carried out directly in living organisms, whether it be mice, naked mole rats, dogs, or humans. This often involves injecting various trial medications or foreign DNA elements and seeing the effect on the living organisms itself, in an endogenous environment (the living entity).
In vitro translates to ‘in glass’, which is the Latin way of saying ‘in an artificial environment’. This is what cell culture is. It is removing cells from the living organism and placing them in a dish and carrying out the experiments in the dish. In vitro experiments can help validate concepts and protocols prior to taking them into living organisms and are an invaluable basis for much of the biology research that happens every day.
What is a cell culture?
Cell culture is a widespread term that just means growing cells in a dish in an incubator. The cells are grown in conditions that mimic their native environment. Depending on the cell type, figuring out the specific conditions can take some experimentation, adjusting parameters like temperature, CO2 concentration, and different nutrients in the growth media.
What can be cultured?
Most cells types can be grown in a dish. In the past few years some researchers have even been pushing the boundaries of this idea and growing entire organs in a dish! There is one group that is trying to develop artificial brains and have even grown them to the point of normal levels of activity. Which is amazing and scary and ethically/morally ambiguous, but that’s probably a topic for a different post.
There are two “varieties” of cells in cultures: primary cells (also referred to as finite cell lines) and immortalized cells (also known as continuous cell lines). Primary cells are taken directly from the tissue of interested (like a lung) by simply grinding and mashing the organ and breaking the cells apart so they can grow on a dish. Specific cell types can be selected for by coating the tissue culture dish with antibiotics or with gelatin (only cells called fibroblasts can attach to gelatin) or other selection agents. This type of cell culture is typically the more challenging of the two, as primary cells often need specific conditions to grow with various nutrients that change depending on the tissue. However, primary cells are a powerful tool for in vitro studies, as they often more accurately portray what’s happening in the organism.
Immortalized cells, on the other hand, are less fragile. These are cells that have been modified to be able to replicate and divide indefinitely. How they have been modified varies a bit based on which cell line it is, but in general the cell’s innate control mechanisms for dividing have been disabled so that there are no signals for the cell to stop dividing. The concept of immortalization is a bit complicated for me to summarize in this post alone, so I might do a follow up post in the future because it can be confusing.
In addition, cancer cells grown in culture are immortalized without having to manually manipulate them. Tumors are just massive clumps of cells that won’t stop growing, because the damage that leads to cancerous cells enables them to avoid cell death and other cell growth constraints. More details about cancer specifically can be found in my dedicated post about it!
Can cells grow indefinitely?
This is a tricky question, because the answer is both yes and no. As I discussed above, cells can be immortalized to continue to grow in culture essentially forever, or cancer cells can be grown forever because they are “naturally” immortalized. There is one cancer cell line that’s incredibly popular, called HeLa cells, that came from one tumor sample (from a woman called Henrietta Lacks, Rebecca Skloot wrote a great book about her if you want to check it out). Yet these cells (which originated from just this one sample) have been used in labs across the world for years. However, these cells can’t just be put in a dish and left for years – they have to be maintained.
If cells are left in a dish unattended, they will eventually all die because they crowd each other out and/or because all the nutrients in the media have been used up. Cell culture maintenance involves changing the media every few days to ensure the cells have enough to “eat” and doing something called splitting the cells – basically transferring some cells to a new culture dish to avoid crowding.
One way to think of splitting cells is this: say you have a car with some rabbits in it. These rabbits are going to do what rabbits do naturally and create even more rabbits. Eventually the car is going to fill up and there won’t be any room for new rabbits. You take a few of these rabbits and transfer them to a new car, where they can continue to create even more rabbits. In this way, your stock of rabbits is never depleted, and you can continue to get more rabbits as you transfer them to more cars. In the case of cell culture, these cells are just tiny microscopic beings, but the concept of crowding and running out of room is the same.
(I love that analogy, it was told to me by a fellow scientist my lab, so I can’t take credit for it).
Through maintenance and splitting, you can grow cells “forever.” On the other hand, one individual cell cannot grow indefinitely. These cell lines survive because the cells keep replicating and creating new cells, but individual cells still die. The total cell population keeps growing though, because the new cells continue to divide as well. When we say a cell is “immortalized,” it really means you can maintain the entire cell line (the population as a whole), not individual cells. Immortalized cells themselves can’t just be split continuously – high passage numbers (one passage = one time split, or putting the cells on a new plate) can cause cells to alter their genetics, which can throw off experiments. Often “stocks” of these cell lines are made by freezing them in liquid nitrogen (temperatures of -140°C), so that fresh cells can always be available if they are needed.
Conclusion
Cell culture is a vital process of many research labs. It allows for experiments to be tested in an artificial, controlled environment so we can see which variables affect outcomes. It also allows for experiments to be done at a quicker pace, as in vivo experiments often take months to fully carry out. Because of this, cell culture experiments can be repeated in a short amount of time, which strengthens experimental results.
As with most experimental procedures, there are drawbacks to using cell culture. While we can try our best to artificially reproduce an in vivo system, we can’t get it exact. Living beings are incredibly complex and replicating that complexity to every minute detail is next to impossible. The best thing for these cells is to keep them as happy as possible because even though cultures aren’t an exact replica, the information we glean from them is irreplaceable.
My advice is this: if you want to be a research scientist (especially in the biology world), cell culture is a skill you must learn. How to grow the common cell types, how to make media, how to work in a sterile environment, all of the steps involved. It will pay off I promise!
Further Reading:
