Resumen de Estudis filogenètics dels receptors de glutamat i les seves subunitats auxiliars actualitzen les seves classificacions i revelen les seves diverses històries evolutives en metazous
Glutamate is the major excitatory neurotransmitter in vertebrate and invertebrate nervous systems. Proteins involved in glutamatergic neurotransmission, and chiefly glutamate receptors and their auxiliary subunits, play key roles in nervous system function. Thus, understanding their evolution and uncovering their diversity is essential to comprehend how nervous systems evolved, shaping cognitive function. Comprehensive phylogenetic analysis of these proteins across metazoans have revealed that their evolution is much more complex than what can be anticipated from vertebrate genomes. This is particularly true for ionotropic glutamate receptors, as their current classification in six classes (AMPA, Kainate, Delta, NMDA1, NMDA2 and NMDA3) would be largely incomplete. New work proposes a classification into 4 subfamilies that encompass 10 classes. Vertebrate AMPA, Kainate and Delta receptors would belong to one of these subfamilies, named AKDF, and the NMDA subunits would constitute another subfamily. Furthermore, two previously unreported subfamilies would also exist, these are referred to as Epsilon and Lambda. On the other hand, protein families containing AMPA receptor auxiliary subunits (ARAS) have experienced less complex evolutionary histories. Nevertheless, vertebrates would have recruited to function as ARAS in the synapse proteins from these families by neo and/or subfunctionalization after gene duplication events occurred in this lineage. Thus, this work favours the hypothesis that nervous system complexity could have evolved not by increasing the set of neurotransmitter receptors in the genome, but by increasing the regulation of such receptors in the synapse.
