Technique: Chemotaxis concepts – Why did the chicken cross the road?

Why did the chicken cross the road? Well, frankly, who knows what induced the chicken to cross the road. Generally, we can assume that the chicken had a reason. Arguably everything we do in everyday life we do for a reason – whether voluntary or involuntary. Like most other creatures in the world, we respond to our environments.

If you show a dog a bone, and then place that on the far side of the room, the dog will run over to get it. But the stimulus doesn’t have to be food. If a person enters the room, a dog will typically rush over to greet it – though whether that greeting is friendly or threatening depends on many factors.  Lack of movement can also be due to the environment that we sense around us. For example, when I often wake up, I am tempted not to get out of bed, because it Is incredibly comfortable where I am, and, for the time being, there is no specific reason to move.  Therefore:

Movement = response to factors signalling that another place is desirable and/or lack of factors signalling that the current location is desirable

Lack of movement = response to factors signalling that the current location is desirable and/or lack of factors signalling another place is desirable

Like whole organisms, cells behave in response to the environments they sense around them. For example, consider cells in the circulation. While initially one thinks of these cells as being simply pushed around by the physical pressures exerted by fluid dynamics, these cells are actually constantly sensing their environments and can respond by clotting, leaving the leaving the blood system and moving into surrounding tissues, or continuing circulating. In contrast, think of skin cells. These cells stay in one place, because they are surrounded by similar cells and supporting layers of cells that provide the signals to stay in place. However, in response to injury, e.g. a paper-cut, the cells quickly change their entire behaviour and can both move into the wound site as well as signal to the blood and immunological cell types necessary for repair.

Outside of the body, in the laboratory setting, it’s easy to study the effect of each movement signal, also known as a chemotactic factor (chemotaxis meaning movement in response to a chemical signal) because we can add the factors in individually and in combinations to observe their exact effects. In this blog I have already discussed a way to measure random cell movement in response to growth factors (September 28: Calculating Cell Velocity). In my next post I will discuss the Boyden Chamber assay for studying directional cell movement in response to factors.

 

And now, my body is telling me I need to move to a location that provides caffeine. I’m off to get some coffee and get back to working on my thesis.

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