Scientists studying the genome of sponges — one of the most primitive and ancientcreatures on Earth — have uncovered a significant clue in their search for the evolutionary origins of the nervous system.
Researchers at the University of California, Santa Barbara, have discovered that while sponges remain the only multicellular animals without a nervous system, they do possess most of the genetic components of synapses, one of the essential building blocks of a nervous system.
The findings were published in the June 6 issue of the journal PLoS ONE, an international open source organization.
Synapses are the connecting points that allow nerve cells totransmit signals and facilitate communication, memory and learning.
While sponges do not possess synapses, a comparison of the genes of the sponge Amphimedon queenslandica to the genesexpressing a human synapse found striking overlap, suggesting sponges possess many of the building blocks needed to create synapses.
Even more surprising, the scientists also found the complex protein structures present in sponges had distinct "signatures," suggesting they probably interact with each other in a manner similar to how information is passed through synapses.
Unravelling the origins of the nervous system is key to understanding a vital and complex part of human biology, said senior author Ken Kosik, the co-director of the university's Neuroscience Research Institute.
The first neurons and synapses appeared in jellyfish, hydra and sea anemones, a group of invertebrates called cnidarians. Sponges predate these creatures, however, and have no synapses or internal organs. However, their bodies do locally contract in response to touch or pressure.
"We look at the evolutionary period between sponges and cnidarians as the period when the nervous system came into existence, about 600 million years ago," said Kosik.
"It is clear that evolution was able to take this entire structure, and, with small modifications, direct its use toward a new function," said Kosik.