Meeting Abstract
Advances in Omics and their implementations to basal metazoan clades (Ctenophora, Porifera, Placozoa, Cnidaria, Bilateria) resulted to revisions of the animal phylogeny and hypotheses of neural evolution. Our analysis suggests that both neurons and synapses evolved independently from different cell lineages recruiting the ancestral machinery for secretion and reception developed in early eukaryotes. Temporal differentiation of cellular phenotypes found in unicellular eukaryotes (as result of their complex life cycles) was substituted and extended by spatial differentiation in metazoans leading to a greater diversity of cell types. Some components of synaptic and neuronal machinery might represent examples of convergent evolution. The most remarkable case is the parallel origins of cell lineages supporting intercellular signaling using various transmitters. Combining data from 20+ phyla, we will discuss how recruitment of various molecular modules together with environmental constrains might lead to independent origins of neurons and synapses across distinct animal clades. The cladistic reconstructions also suggest that neuronal centralization and mosaic formation of complex brains evolved at least 12 times across the animal kingdom. We define neurons as a functional rather than a genetic category. Neurons are polarized secretory cells specialized for directional propagation of electrical signals leading to release of intracellular messengers – features that enable them to transmit signals, primarily chemical in nature, beyond their immediate neighbors without affecting all intervening cells en route. However, using an array of molecular markers within some animal lineages one can recognize homologous neuronal lineages. These examples and criteria for homologization of distinct cell lineages will be discussed toward reconstruction of natural classification of neurons or NeuroSystematics.
