14 DAY TRIAL // Scientists in the United States have recently determined the answer to an ages-old question – which came first, the animal nervous system or its components? Experts in Texas say that indeed at least one of the vital components in the animal nervous system developed ahead of the larger structure did.
In a series of experiments carried out at the University of Texas in Austin (UTA), investigators found out that sodium channels appeared long before nervous systems did. The former are an essential component of these systems.
According to the conclusions of the new study, the channels appeared a long time before the first nervous system appear in jellyfish-like animals. This happened around 600 million years ago.
Until now, scientists were convinced that the first channels appeared around the same time, but the new study pushes back their emergence date considerably. The announcement was made by UTA professor of neurobiology Harold Zakon.
The expert conducted the work with colleague professor David Hillis and with graduate student Benjamin Liebeskind, both at the university. Details of the research were published in the latest issue of the esteemed journal Proceedings of the National Academy of Sciences (PNAS).
In order to understand the role of sodium channels, you need to think of a neuron in terms of a complex, advanced piece of machinery. These cells are covered by a membrane through which chemicals may pass only at designated points, called channels.
Sodium can flow into the neurons only when these channels are opened. Otherwise, the membrane is impermeable to the chemicals. The presence of sodium in nerve cells is absolutely essential for their ability to generate electrical signals.
The gene that control the development of these sodium channels was recently discovered in the genome of a choanoflagellate, a single-celled microorganism that lived way before jellyfish-like creatures did.
This discovery would also appear to imply that the development of sodium channels did not only precede the development of nervous systems, but also the evolution and emergence of multicellular lifeforms.
“These genes were then co-opted by the nervous systems evolving in multi-cellular animals. This study shows how complex traits, such as the nervous system, can evolve gradually, often from parts that evolved for other purposes,” Hillis says.
The expert also holds an appointment as the Alfred W. Roark Centennial professor in natural sciences at UTA. “Evolutionarily novel organs do not spring up from nowhere, but from pre-existing genes that were likely doing something else previously,” Zakon concludes.