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Early Evolution of Ionotropic GABA Receptors and Selective Regimes Acting on the Mammalian-Specific

Summary: Early Evolution of Ionotropic GABA Receptors and
Selective Regimes Acting on the Mammalian-Specific
Theta and Epsilon Subunits
Christopher J. Martyniuk1¤
, Ste´phane Aris-Brosou1,2
*, Guy Drouin1
, Joel Cahn1
, Vance L. Trudeau1
1 Department of Biology and Centre for Advanced Research in Environmental Genomics, University of Ottawa, Ottawa, Ontario, Canada,
2 Department of Mathematics and Statistics, University of Ottawa, Ottawa, Ontario, Canada
Background. The amino acid neurotransmitter GABA is abundant in the central nervous system (CNS) of both invertebrates
and vertebrates. Receptors of this neurotransmitter play a key role in important processes such as learning and memory. Yet,
little is known about the mode and tempo of evolution of the receptors of this neurotransmitter. Here, we investigate the
phylogenetic relationships of GABA receptor subunits across the chordates and detail their mode of evolution among
mammals. Principal Findings. Our analyses support two major monophyletic clades: one clade containing GABAA receptor a,
c, and e subunits, and another one containing GABAA receptor r, b, d, h, and p subunits. The presence of GABA receptor
subunits from each of the major clades in the Ciona intestinalis genome suggests that these ancestral duplication events
occurred before the divergence of urochordates. However, while gene divergence proceeded at similar rates on most receptor
subunits, we show that the mammalian-specific subunits h and e experienced an episode of positive selection and of relaxed
constraints, respectively, after the duplication event. Sites putatively under positive selection are placed on a three-


Source: Aris-Brosou, Stéphane - Department of Biology, University of Ottawa


Collections: Biology and Medicine