Issue 41

Biomedical science in action! Investigating brain stem cells using mouse genetics, microscopes, and radiation.

Cells are a fundamental unit of life, and our bodies are made up of trillions of them. There are many different types of cell that function in specific ways, and if our cells don’t do their job properly, disease can happen. What tools can we use to figure out what certain types of cell do in our brains?

It would be an understatement to say that our brains are hugely important. Your brain controls everything you do, and it is what makes you, well, you. But did you know our brains also produce hormones (known as neurohormones), which regulate our bodies in subtle but crucial ways?

Neurohormones are chemicals which flow around in our blood and regulate things like metabolism, stress, growth, reproduction, and lactation (production of milk). These neurohormones are made in two parts of the brain. One part, called the pituitary gland, dangles underneath the brain like a tiny punch bag (or maybe a bit like the basket beneath a hot air balloon?). The other part, known as the hypothalamus, sits just above the pituitary like a hat or a roof, and makes special neurohormones which actually control the release of other neurohormones from the pituitary gland (or pituitary, for short). In that way, the hypothalamus is kind of ‘in charge’ of the pituitary. Together, they form what is known as the hypothalamic-pituitary axis.

When the hypothalamus and the pituitary don’t do their jobs properly, the levels of our neurohormones can change in abnormal ways, and that can have profound impacts on health and wellbeing. For example, growth hormone deficiency results in a lack of normal growth with age. To give another example, a lack of thyroid-stimulating hormone can make us feel tired, cold and gain weight. Conditions like these can arise due to genetic causes, age, injuries, and even cancer.

One other way that these hormonal problems can arise is as a side-effect of radiotherapy, more specifically, radiation used to prevent the spread of cancer to the brain. This is where my research and I come in. Why does this happen? And can we do anything to stop it? Also, what can we learn from this phenomenon about the functions of brain cells in the hypothalamus and pituitary under normal conditions, as well as in disease?

To attempt to answer these questions, I perform experiments with mice and try to unpick the biology behind these problems. Mice are incredibly useful (not to mention cute) and it is a privilege to be able to do my research with them. There are many important laws and regulations that control how we can use mice for scientific research, which ensures that we do good science. We use the smallest number of mice needed to carry out the experiment and use methods to make sure they don’t feel pain We also abide by the principles of the ‘3 R’s’: Reduce, where possible, the number of animals used, Refine your experiments to ensure they get the most information in the most effective and economic way possible, and finally, Replace animals in your research with alternatives, where possible, such as using computers or human cell lines.

In a practical sense, mice are useful because they reproduce quickly and are easy to house and look after, but they also have similar organs, cells and tissues as humans. We also have an excellent understanding of mouse biology, including their genetics, which means experiments can be performed under well-defined conditions (meaning it is easier to make a link between causes and effects in experiments). Genetic tools that have been developed for use in mice also allow scientists to perform very elegant and informative experiments, such as fluorescently labelling cells, specifically killing certain cells, or getting rid of genes or bits of genes (using techniques like CRISPR, which you may have heard about in the news, since the scientists who discovered it won the Nobel Prize in 2020).

The basis of many of these genetic techniques relies on the fact that specific cell types (i.e., neurons, muscle cells, skin cells, etc.) express specific genes or markers. Skin cells express a gene called keratin 14, for example, where nerve cells express beta-3-tubulin. If you can insert a bit of DNA – containing your fluorescent protein, for example – into the same region of DNA that the cell specific gene, or marker, is produced from, then you can restrict the expression of your extra bit of DNA to that cell type as well! As in my experiments, the results can be that all of the brain stem cells are green in colour (they aren’t green normally, you know!). This makes it very easy to identify and investigate the certain types of cells that we are interested in.

For example, in order to understand a bit more about regulation of the hypothalamus and pituitary in mice, I have fluorescently labelled mouse brain stem cells, based on the marker genes that they express. Stem cells are a type of cell that make other cells. Labelling the stem cells this way allows me to use microscopes to see where those cells live, what structures they form, and which other cells they touch and talk to. Finding the answers to these questions is the first step in figuring out what the job of these cells might be, and whether it could relate to the regulation of neurohormones.

However, a better experiment is to get rid of the same brain stem cells, and see what happens to the mouse and the levels of neurohormones in the blood and pituitary (experiments like these are known as loss of function experiments). Again, I use a genetic technique to do this. A special type of protein, called a receptor protein, can be inserted into the brain cells that I am interested in. When I inject a chemical in to the mice, only cells that have the special receptor undergo cell death (called apoptosis). I can then study the mouse brain and see whether there are any changes in the structure of neurons or the number of nerve endings. I can also dissect the pituitary gland, and use a special technique called radioimmunoassay to measure the amount of neurohormones.

Performing the radioimmunoassay is fun, because it is more to do with physics than biology! In principle, the idea is to use radioactive chemicals to label neurohormones from our sampled mouse pituitary glands. I can then measure the amount of radiation produced by the samples, and infer from that what the level of neurohormones in each sample must be.

Now, remember that I said one way that deficiencies in neurohormones can come about is due to a side effect of some types of radiotherapy? Here is where my research touches upon radiation science again. One other, very important experiment that I do is to basically mimic radiotherapy with my mice, and see if they develop the same side effects as humans! To do this, I use a machine which produces X-rays, which I can direct towards specific areas of the mouse brain. Like with my other experiments, I can then measure the levels of neurohormones, as well as look at brain stem cells, and see if there are any interesting changes.

Overall, I feel like I have one of the best jobs in the world! While I do a lot of science in the lab, I also spend time planning my experiments, as well as writing up the results, and presenting my research to other scientists. I love the people that I work with, and I genuinely learn something new every day! While my research is on-going, I am thrilled to go to work and be involved in something that is not only exciting, but which I believe is both important and helpful to others. I really hope that, one day, the work I have done (and will do) will help in some way in either preventing or curing disease.

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Richard Clayton, PhD
Postdoctoral Research Scientist, Francis Crick Institute

Photo of Richard Clayton

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