Meeting Abstract
10.5 Friday, Jan. 4 Genomic Bases for Independent Origins of Neurons and Complex Brains: New Insights from RNA-seq and genomic sequencing of basal metazoans, basal deuterostomes and molluscs MOROZ, L.L.; University of Florida moroz@whitney.ufl.edu
The origin of neurons and complex centralized brains are two major evolutionary transitions in the history of animals. How many times might complex brains and neurons have evolved? Monophyly (e.g. the presence of a centralized nervous system in urbilateria) vs polyphyly (multiple origins by parallel centralization of nervous systems within several lineages) are two historically conflicting scenarios to explain such transitions. To reconstruct the parallel evolution of nervous systems, genomic and metabolomic approaches have been implemented to probe enigmatic neurons of basal metazoans (including 8 ctenophores) and basal deuterostomes, as well as 23 species of gastropod and cephalopod molluscs (including Nautilus, Sepia, Loligo, Octopus). 1) Recent phylogenomic and cladistic analysis of RNA-seq data suggests that complex brains may have independently evolved at least 9-11 times within different animal lineages. Indeed, even within the phylum Mollusca cephalization might have occurred at least 5 times. 2) Cladistic, genomic and metabolomic analyses imply that neurons themselves evolved more than once (e.g. Ctenophores vs other animals). Emerging molecular data further suggest that at the genomic level neural specification might have been achieved by changes in expression of just a few transcriptional factors – not surprising since such events might happen multiple times over 700 million years of animal evolution. Ancestral polarized secretory cells were likely involved in coordination of ciliated locomotion in early animals, and these cells can be considered as evolutionary precursors of neurons within different lineages. Under this scenario, the origins of neurons can be linked to adaptations to stress/injury factors in the form of an integrated regeneration-type cellular response with secretory signaling peptides as early neurotransmitters.
