title: Neocortex expansion is linked to size variations in gene families with chemotaxis, cell-cell signalling and immune response functions in mammals.
abstract: Increased brain size is thought to have played an important role in the evolution of mammals and is a highly variable trait across lineages. Variations in brain size are closely linked to corresponding variations in the size of the neocortex, a distinct mammalian evolutionary innovation. The genomic features that explain and/or accompany variations in the relative size of the neocortex remain unknown. By comparing the genomes of 28 mammalian species, we show that neocortical expansion relative to the rest of the brain is associated with variations in gene family size (GFS) of gene families that are significantly enriched in biological functions associated with chemotaxis, cell-cell signalling and immune response. Importantly, we find that previously reported GFS variations associated with increased brain size are largely accounted for by the stronger link between neocortex expansion and variations in the size of gene families. Moreover, genes within these families are more prominently expressed in the human neocortex during early compared with adult development. These results suggest that changes in GFS underlie morphological adaptations during brain evolution in mammalian lineages.
authors.affiliation: Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, UK School of Life Sciences, University of Lincoln, Lincoln LN6 7TS, UK Milner Centre for Evolution, University of Bath, Bath BA2 7YA, UK.
authors.forename: Atahualpa
authors.initials: A
authors.lastname: Castillo-Morales
authors.affiliation: Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, UK School of Life Sciences, University of Lincoln, Lincoln LN6 7TS, UK Milner Centre for Evolution, University of Bath, Bath BA2 7YA, UK.
authors.forename: Jimena
authors.initials: J
authors.lastname: Monzón-Sandoval
authors.affiliation: Culture and Environment: Psychology, Bath Spa University, Bath BA2 9BN, UK.
authors.forename: Alexandra A
authors.initials: AA
authors.lastname: de Sousa
authors.affiliation: Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, UK Milner Centre for Evolution, University of Bath, Bath BA2 7YA, UK a.urrutia@bath.ac.uk.
authors.forename: Araxi O
authors.identifier: 0000-0001-9011-8675
authors.initials: AO
authors.lastname: Urrutia
authors.affiliation: School of Life Sciences, University of Lincoln, Lincoln LN6 7TS, UK hgutierrez@lincoln.ac.uk.
authors.forename: Humberto
authors.identifier: 0000-0002-5021-8636
authors.initials: H
authors.lastname: Gutierrez
mesh_terms: D000818:Animals; D002450:Cell Communication; D002633:Chemotaxis / Q000235:genetics*; D018507:Gene Expression Regulation, Developmental; D063990:Gene Ontology; D023281:Genomics; D006801:Humans; D008322:Mammals / Q000033:anatomy & histology / Q000235:genetics*; D005810:Multigene Family; D019579:Neocortex / Q000033:anatomy & histology* / Q000254:growth & development; D009929:Organ Size; D010802:Phylogeny
keywords: brain size; encephalization; gene family size; neocortex