Wednesday, June 20, 2012

New clues about origin of the nervous system found

Our nervous system is what sets us apart from other animals. We are conscious of ourselves and our surroundings, and our brain makes us able to create things that greatly extend our capabilities of survival. Human beings have a complex nervous system with a central part of which the brain is the most important. Simple organisms lack this central part, and just use simple 'wiring' to control body functions. In evolution, the nervous system has become increasingly complex, and scientists from the University of California in Santa Barbara have found clues about the origin of this magnificent system.

In order to investigate how evolution could have created a nervous system that controls body functions, the scientists studied sponges. According to them, the sponge is a relevant animal to study when aiming to find evolutionary traces of the nervous system. This is because a common ancestor supposedly 'branched off' somewhere in evolution and formed animals with a neural network, therefore forming the foundation of many organisms alive today, including us. Because the ancestor we share with sponges was supposedly one of the first with neuron-like connections, it is interesting to find out why the other branch, the sponges, did not develop a nervous system.
Simplified version of the 'tree of life'. Sponges and vertebrates (where we belong to) branch off early in evolution. (source)
By analysing the genome of A. queenslandica, a type of sponge, the scientists found several genes that are used in other organisms to make parts of neural connections. They showed sponges contain the necessary genes to create synapses, which are the junctions between neural cells, and are used for exchange of communicative signals. Despite having the right blueprint for synaptic communication between cells, a neural network does not exist in sponges, which is why the scientist turned to analysing the activity of said genes.

Having a book to convey information is useless if nobody reads it, and the same is true for DNA: having a particular set of genes is useless if the cell does not 'read' them. Eventually, the information needs to be translated into proteins, the building blocks for cellular structures. The scientists found that the synaptic genes in sponges are in fact read by the cell, but their activity is not synchronized correctly. Because the 'gene reading' was intermittently shut off, it is likely that cells were unable to use the genetic blueprint correctly, leaving them unable to utilize the potential for synapses.

There is more to be discovered about the origin of the neural network, but it is clear that the evolutionary steps required to build a nervous system involved more than just having the right set of genes and using them. There is some form of coordination going on that some animals got right, allowing them to form the first neural network, while the sponges were left with just the blueprint. As is visible from the difference between human beings and sponges, this was a rather important step in evolution. There are of course more important evolutionary steps that lead up to us, so future research by the University of California in Santa Barbara will take an even closer look at synapse formation and its origin.

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