PT - JOURNAL ARTICLE AU - Julia E. Pedersen AU - Christina A. Bergqvist AU - Dan Larhammar TI - Evolution of the muscarinic acetylcholine receptors in vertebrates AID - 10.1523/ENEURO.0340-18.2018 DP - 2018 Oct 24 TA - eneuro PG - ENEURO.0340-18.2018 4099 - http://www.eneuro.org/content/early/2018/10/24/ENEURO.0340-18.2018.short 4100 - http://www.eneuro.org/content/early/2018/10/24/ENEURO.0340-18.2018.full AB - The family of muscarinic acetylcholine receptors (mAChR) consists of five members in mammals, encoded by the CHRM1-5 genes. The mAChRs are G protein-coupled receptors (GPCRs) which can be divided into two subfamilies: M2 and M4 receptors coupling to Gi/o and M1, M3 and M5 receptors coupling to Gq/11. However, despite the fundamental roles played by these receptors their evolution in vertebrates has not yet been fully described. We have combined sequence-based phylogenetic analyses with comparisons of exon-intron organization and conserved synteny in order to deduce the evolution of the mAChR receptors. Our analyses verify the existence of two ancestral genes prior to the two vertebrate tetraploidizations (1R and 2R). After these events, one gene had duplicated resulting in CHRM2 and CHRM4 and the other had triplicated forming the CHRM1, CHRM3 and CHRM5 subfamily. All five genes are still present in all vertebrate groups investigated except the CHRM1 gene which has not been identified in some of the teleosts or in chicken or any other birds. Interestingly, the third tetraploidization (3R) that took place in the teleost predecessor resulted in duplicates of all five mAChR genes of which all ten are present in zebrafish. One of the copies of the CHRM2 and CHRM3 genes and both CHRM4 copies have gained introns in teleosts. Not a single separate (non-tetraploidization) duplicate has been identified in any vertebrate species. These results clarify the evolution of the vertebrate mAChR family and reveal a doubled repertoire in zebrafish, inviting studies of gene neo- and sub-functionalization.Significance statement Despite their pivotal physiological role, the evolution of the muscarinic acetylcholine receptors (mAChR) has not yet been resolved. By investigating the genomes of a broad selection of vertebrate species and combining three different types of data, namely sequence based phylogeny, conserved synteny and intron organization, we have deduced the evolution of the mAChR genes in relation to the major vertebrate tetraploidizations (1R, 2R and 3R). Our analyses show that all vertebrate mAChR gene duplications resulted from the tetraploidizations. Interestingly, following 3R, zebrafish doubled its gene number, resulting in the ten mAChR genes present. By knowing how and when the mAChR genes arose, studies of receptor subtype specialization and possible neo- or sub-functionalization can follow.