Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Functional Conservation and Genetic Divergence of Chordate Glycinergic Neurotransmission: Insights from Amphioxus Glycine Transporters

Version 1 : Received: 21 October 2021 / Approved: 25 October 2021 / Online: 25 October 2021 (12:45:26 CEST)

A peer-reviewed article of this Preprint also exists.

Bozzo, M.; Costa, S.; Obino, V.; Bachetti, T.; Marcenaro, E.; Pestarino, M.; Schubert, M.; Candiani, S. Functional Conservation and Genetic Divergence of Chordate Glycinergic Neurotransmission: Insights from Amphioxus Glycine Transporters. Cells 2021, 10, 3392. Bozzo, M.; Costa, S.; Obino, V.; Bachetti, T.; Marcenaro, E.; Pestarino, M.; Schubert, M.; Candiani, S. Functional Conservation and Genetic Divergence of Chordate Glycinergic Neurotransmission: Insights from Amphioxus Glycine Transporters. Cells 2021, 10, 3392.

Journal reference: Cells 2021, 10, 3392
DOI: 10.3390/cells10123392

Abstract

Glycine is an important neurotransmitter in vertebrates, performing both excitatory and inhibitory actions. Synaptic levels of glycine are tightly controlled by the action of two glycine transporters, GlyT1 and GlyT2, located on the surface of glial cells and glycinergic or glutamatergic neurons, respectively. Glycinergic neurotransmission in invertebrates has so far only been investigated in a very limited number of species, and, although it was suggested that its functions are to some extent conserved with vertebrates, the evolution of glycinergic neurotransmission remains very poorly understood. Here, by combining phylogenetic and gene expression analyses, we characterized the glycine transporter complement of amphioxus, an important invertebrate model for studying the evolution of chordates. We show that amphioxus possesses three glycine transporter genes, two of which (GlyT2.1 and GlyT2.2) are closely related to GlyT2 of vertebrates, while the other (GlyT) is a member of an ancestral clade of deuterostome glycine transporters. While expression of GlyT2.2 is predominantly non-neural, GlyT and GlyT2.1 are widely expressed in the amphioxus nervous system and are characterized by differential expression in neurons and glia, respectively. However, in vertebrates, glycinergic neurons express GlyT2 and glia GlyT1, suggesting that the evolution of the chordate glycinergic system was accompanied by complex genetic remodeling leading to the paralog-specific inversion of gene expression. Albeit this genetic divergence between amphioxus and vertebrates, we found strong evidence for a general conservation of the role of glycinergic neurotransmission during larval swimming, allowing us to hypothesize that the neural networks controlling the rhythmic movement of chordate bodies are homologous.

Keywords

GlyT; glia; nervous system evolution; central pattern generator; locomotion; cephalochordates

Subject

BIOLOGY, Anatomy & Morphology

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