Comparative analysis of gene expression in mammalian claustrum subdivisions

The claustrum is a major connectivity hub for cortical circuits and has recently become a nexus for research on cognition, brain state transitions, and mood disorders. While most recent studies focus on mice, there are ongoing debates regarding the definition of rodent claustrum borders, subregions, development, and constitutive cell types. Hence, problems mount when attempting to compare the claustrum across mammals with diverging brain size and morphology. In particular, understanding the primate claustrum remains challenging, because numerous incongruent parcellation schemes for the primate claustrum exist. Here, we propose that evolutionarily conserved subdivisions of the claustrum complex can be identified across mammals by combining gene expression patterns, cytoarchitecture, and topological position. To this end, we compare selected claustrum-specific genes, such as Nurr1, Oprk1, Lxn, and Cdh8, in several species, including rats, Etruscan shrews, tree shrews, marmoset monkeys, and macaque monkeys, to examine patterns of claustrum subdivision across these species.