Clues to Nervous System Evolution Found in Nerve-Less Sponge

Sponges have all the genes necessary to have a nervous system, however they do not contain neurons at all. Research done on sponges has led to shocking discoveries of how the nervous system and gene expression are linked.
Photo courtesy of neurosciencenews.com.

It has always been question how sponges and animals have come from the same ancestry line but sponges lack the nervous system that animals have. Scientists realized that they could study the evolution of sponges to understand characteristics of the nervous systems in animals and the evolution of the nervous system.

            Sponges have all of the genes required to have the complex nervous system and create a synapse (mechanism that sends and receives signals), however, something happened over evolution that prevented sponges from having any neurons at all.

            Many scientists are interested in this idea and one scientist in particular, Danielle Bassett, decided to study sponge RNA and followed sponge activity. She looked at different stages of development in a sponge that lives on the Great Barrier Reef in Australia to analyze the genes that code for proteins that make up a synapse.

            What was found? Bassett found that the sponges would turn on and off unlike in animal cells that are either all on or all off.  This finding gave a good indication at the difference between animals and sponges, that sponges had cells that are not coordinated like animals. Sponges lacked the ability to express all the genes at once, as if they couldn’t be connected together. This prevented the creation of the synapse in the sponge. Therefore, throughout the evolution path, animals and sponges came from a common ancestry that had all the genes necessary to express a synapse, however animals split off because they have the ability to wire this network together.

            This discovery led to the idea of gene expression. Sponges lack the gene expression capabilities that animals have when it comes to neurons. Sponges can’t express these genes all at once but rather have an on an off thing going on. This research is just the beginning of much more information to be found about the evolution of the human brain!

Blog Post Author: Abby Mulligan Section 124-25