February 14, 2012
Gravity potentially affects all biological processes on Earth, even though this may be hard to believe while we watch flies walking around on our ceilings as though gravity did not matter to them at all. Of course, gravity is only one factor, and other factors such as adhesion or buoyancy determine whether an organism falls off the ceiling, say, or how long it takes an organism to settle to the ground.
We’ve known for a long time that humans are harmed by long periods in low-gravity environments. Astronauts return from space with muscle atrophy and reduced bone mass. These effects seem to get worse over time, so understanding the effects of gravity on human physiology is essential when planning long-distance space flights. Studying the effects of low gravity in space craft and space stations is expensive. Anyone who has spent time working in a laboratory knows that many experiments have to be redone numerous times just to get the procedures to work properly. If a key step in carrying out an experiment on, say, the response of cells to lack of gravity, is “shoot the experiment into space and keep it there for two months” then it will take a very long time and a lot of money to get results one might need to make sense of low-gravity biology. Therefore, it would be nice to have an anti-gravity machine in our Earth-bound laboratories to run experiments without the cost and scheduling constraints imposed by space flight.
There is a way to simulate weightlessness at a small scale in the lab. A team of researchers from several European institutions have used magnetism to offset the effects of gravity at the cellular level. The method is called diamagnetic levitation. (Another method for simulating anti-gravity uses a “Random Positioning Machine” (RPM).) Some materials—diamagnetic materials—are repelled by a magnetic field. Water and most biological tissues fall into this category. A very powerful magnetic field can be applied to these tissues to offset the effects of gravity, so molecules moving about and doing their thing inside cells do so as though there were no gravity acting on them. According to a recent study, it appears that gene expression is affected by gravity. (The paper is published in BMC Genomics and is available here.)
The magnet used in this experiment produces a field with a force of 11.5 Tesla (T). The Earth’s magnetic field is equal to about 31 micro Teslas. The magnet holding your shopping list to your refrigerator is about .005 Tesla, the magnets in a loudspeaker are about 1 to 2 Teslas in strength, and the magnetic force of an MRI or similar device, for medical imaging, is usually about 3 Teslas or less. If you were to attach a magnet of 11.5 Teslas to your refrigerator, you would not be able to pry it off.
In this experiment, the magnet was used to “levitate” fruit flies for 22 days as they developed from embryos to larvae to pupae and eventually to adults. The flies were kept at a certain distance above the magnet where the net repulsive effect of the magnet on the water and other molecules was equal to and opposite of the effects of gravity. Other flies were placed below the magnet at the same distance, where they experienced the equivalent of double the Earth’s gravity.
The study examined how the expression of genes differed depending on the simulated gravitational field as well as in a strong magnetic field that did not simulate a change in gravity. Doubling the Earth’s gravity changed the expression of 44 genes, and canceling out gravity altered the expression of more than 200 genes. Just under 500 genes were affected by the magnetic field alone, with expression of the genes being either increased or decreased. The researchers were able to subtract the effects of magnetism from the effects of increased or decreased gravity and thus isolate which genes seemed to be most sensitive to changes in gravity alone. According to the researchers, “Both the magnetic field and altered gravity had an effect on gene regulation for the flies. The results of this can be seen in fly behaviour and in successful reproduction rates. The magnetic field alone was able to disrupt the number of adult flies from a batch of eggs by 60%. However the concerted effort of altered gravity and the magnet had a much more striking effect, reducing egg viability to less than 5%.”
The most affected genes were those involved in metabolism, the immune system’s response to fungi and bacteria, heat-response genes and cell signalling genes. This indicates that the effects of gravity on the developmental process in animals is profound.
The most important outcome of this research is probably the proof of concept: It demonstrates that this technique can be used to study the effects of low gravity on biological processes. We can expect more-refined results that inform us of specific processes that are altered by gravity, and possibly develop ways of offsetting those effects for humans or other organisms on long-distance space flight. Eventually, we may be able to send a fruit fly to Mars and return it safely.
Herranz, R., Larkin, O., Dijkstra, C., Hill, R., Anthony, P., Davey, M., Eaves, L., van Loon, J., Medina, F., & Marco, R. (2012). Microgravity simulation by diamagnetic levitation: effects of a strong gradient magnetic field on the transcriptional profile of Drosophila melanogaster BMC Genomics, 13 (1) DOI: 10.1186/1471-2164-13-52
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