Science & Technology - Posted by Sonia Fernandez-UCSB on Friday, July 6, 2012 14:25 - 0 Comments
Evolution clues from nerve-free sponges
UC SANTA BARBARA (US) — Except for their ‘unwired’ network of neural synapses, sponges and the rest of the animal world may not be so distantly related after all.
Straight from the Source
“If you’re interested in finding the truly ancient origins of the nervous system itself, we know where to look,” says Kenneth Kosik, professor of neuroscience research in the Department of Molecular, Cellular & Developmental Biology (MCDB), and co-director of the Neuroscience Research Institute (NRI).
That place, says Kosik, is the evolutionary period of time when virtually the rest of the animal kingdom branched off from a common ancestor it shared with sponges, the oldest known animal group with living representatives.
Something must have happened to spur the evolution of the nervous system, a characteristic shared by creatures as simple as jellyfish and hydra to complex humans, according to Kosik.
A previous sequencing of the genome of the Amphimedon queenslandica—a sponge that lives in Australia’s Great Barrier Reef—showed that it contained the same genes that lead to the formation of synapses, the highly specialized characteristic component of the nervous system that sends chemical and electrical signals between cells.
Synapses are like microprocessors, says Kosik, who explains that they carry out many sophisticated functions: They send and receive signals, and they also change behaviors with interaction—a property called “plasticity.”
“Specifically, we were hoping to understand why the marine sponge, despite having almost all the genes necessary to build a neuronal synapse, does not have any neurons at all,” says the paper’s first author, postdoctoral researcher Cecilia Conaco.
“In the bigger scheme of things, we were hoping to gain an understanding of the various factors that contribute to the evolution of these complex cellular machines.”
This time the scientists, including Danielle Bassett, from the Department of Physics and the Sage Center for the Study of the Mind, and Hongjun Zhou and Mary Luz Arcila, from NRI and MCDB, examined the sponge’s RNA (ribonucleic acid), a macromolecule that controls gene expression. They followed the activity of the genes that encode for the proteins in a synapse throughout the different stages of the sponge’s development.
“We found a lot of them turning on and off, as if they were doing something,” says Kosik. However, compared to the same genes in other animals, which are expressed in unison, suggesting a coordinated effort to make a synapse, the ones in sponges were not coordinated.
“It was as if the synapse gene network was not wired together yet,” says Kosik. The critical step in the evolution of the nervous system as we know it, he says, was not the invention of a gene that created the synapse, but the regulation of preexisting genes that were somehow coordinated to express simultaneously, a mechanism that took hold in the rest of the animal kingdom.
The work isn’t over, says Kosik. Plans for future research include a deeper look at some of the steps that lead to the formation of the synapse and a study of the changes in nervous systems after they began to evolve.
“Is the human brain just a lot more of the same stuff, or has it changed in a qualitative way?” he asks.
Bernard M. Degnan of the University of Queensland is an additional co-author of the study.
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