Retrograde Tracing

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Science  29 Jun 2007:
Vol. 316, Issue 5833, pp. 1814
DOI: 10.1126/science.316.5833.1814c

Synapses, the essential plug-socket assemblies for animal nervous systems, are intricate molecular structures. Large complexes of proteins in both the pre- and postsynaptic neurons manage the transfer of information, membrane vesicles come and go, and molecular signals light up the wires. How did this chemical connector evolve?

Sakarya et al. have analyzed molecular components of sponges, which represent a primitive branch of the evolutionary tree of animals. Sponges do not have a nervous system or synapses. In animals that do have nervous systems and synapses, the postsynaptic density is composed of probably nearly a thousand proteins. The authors performed a comparative analysis of genomes and cataloged synapticlike proteins in the sponge Amphimedon queenslandica, which lacks neurons, and the cnidarian Nematostella vectensis, which has a comparatively simple nerve net. Identification of many genes in the sponge similar to the postsynaptic density genes of more complex nervous systems suggests that similar macromolecular structures are assembled even in the sponge. Such structures may have been co-opted during evolution for use in nascent nervous systems. — PJH

PLoS ONE 2, e506 (2007).

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