Most of us probably don't spend a lot of time thinking about vesicles.
Indeed, it is not a term that would likely be used in common conversation. "How are your vesicles doing today?" just doesn't sound quite right.
For Randy W. Schekman, James E. Rothman, and Thomas C. Sudhof, vesicles have played an important part in their academic careers. As recipients of this year's Nobel Prize in Physiology and Medicine, their citation reads: "for their discoveries of machinery regulating vesicle traffic, a major transport system in our cells".
Vesicle transport, though, is critical for the proper function of cells and perhaps more importantly for the critical function of thinking. That is, if you are going to think about vesicles then you need vesicles in order to do that thinking.
The way that neurons conduct signals is broken into two parts. The first is "electrochemical" and based on concentration gradients. The nerve cells have a high concentration of sodium ions outside and a high concentration of potassium ions inside. The difference in concentrations sets up a voltage potential of about -65 mV across the neuronal membrane.
Signals are then transmitted along a neuron by the influx of sodium ions into the cell followed by the outflow of potassium ions from the cell. The result is a unidirectional flow of electrical potential from the cell body down the axon.
But the whole process is not electrochemical. At the end of a nerve, the signal needs to be transmitted from one neuron to the next across something called "the synaptic cleft". Essentially, it is a small gap between neurons where the flow of information is controlled by chemical compounds called "neurotransmitters".
The discovery of neurotransmitters and how they work is for another column but how they get introduced into the synapse depends on vesicles.
The sending neuron - the one that has been electrochemically stimulated - contains the neurotransmitter. It could just randomly send out waves of compounds but that would cause the receiving neuron to constantly be firing or misfiring.
Instead, the sending neuron wraps a small amount of the neurotransmitter inside of a membrane. The product is a bit like a molecular water balloon and it is these water balloons that are vesicles.
When a signal is received at the end of the sending neuron, some of the vesicles fuse with the neuronal membrane and temporarily create a hole or pocket from which the neurotransmitter can diffuse. It is bit different from a water balloon in that the vesicle doesn't simply go splat on the inside of the membrane but fuses with the membrane.
The size of a signal is then controlled by the number of vesicles that fuse with a membrane as each vesicle releases only a small amount of the neurotransmitter. One vesicle would not cause much of a stir on the receiving end - say the pain from a pinch. Many vesicles fusing could result in a feeling of intense point leading someone to pass out.
Vesicles are not found only in neurons. Cells throughout the body use them. Essentially, the inner workings of a cell are a chemical factory producing a myriad of products - everything from hormones to cholesterol to proteins. The vesicles are the delivery mechanism that collects the products of a chemical reaction in one part of the cell and moves those compounds throughout the cell to the appropriate location for use.
Indeed, as in the case of neurons, they can even transport the cells chemical right out of the cell entirely.
We know that all of this happens but it was Schekman, Rothman, and Sudhof who worked out how it happens.
Randy Schekman used yeast cells as models. As single celled organisms, yeast are much simpler to study than multicellular species. He was able to show that mutations in certain genes could result in changes to the number and size of vesicles formed. From this, he was able to determine the proteins involved in the process.
James Rothman was looking at complementary functions through cellular biology and he was able to identify the proteins on the surface of vesicles that allowed them to recognize the receptor sites in the membranes within the cells. The fact that the proteins he identified were the same ones that Schekman was finding important for vesicle formation provided validation for each other's research.
Thomas Sudhof was actually working on vesicle fusion in neurons and was able to identify the molecular machinery that actually initiates the process in which a vesicle fuses with the membrane. The process is sensitive to calcium ions which trigger the release of neurotransmitters at a specific moment in time.
We might not think much about vesicles in our daily lives but without these little molecular balloons, life as we know it would not exist on this planet.
