Molecular diversity and evolution of neuron types in the amniote brain

Abstract

The existence of evolutionarily conserved regions in the vertebrate brain is well established. The rules and constraints underlying the evolution of neuron types, however, remain poorly understood. To compare neuron types across brain regions and species, we generated a cell type atlas of the brain of a bearded dragon and compared it with mouse datasets. Conserved classes of neurons could be identified from the expression of hundreds of genes, including homeodomain-type transcription factors and genes involved in connectivity. Within these classes, however, there are both conserved and divergent neuron types, precluding a simple categorization of the brain into ancestral and novel areas. In the thalamus, neuronal diversification correlates with the evolution of the cortex, suggesting that developmental origin and circuit allocation are drivers of neuronal identity and evolution.

Development of subdomains in the medial pallium of Xenopus laevis and Trachemys scripta: Insights into the anamniote-amniote transition

“…In Trachemys scripta, the Satb1/2 cell population is no longer expressed in adult individuals (present results). Furthermore, in agreement with our results in Xenopus laevis (present results), the presence of Mef2c expressing cells in the mammalian hippocampus (Hain et al, 2022) and in the medial cortex of reptiles (Tosches et al, 2018;Hain et al, 2022), as well as EGFR cells in the mammalian hippocampus, involved in the maintenance of progenitors, have been described (Aguirre et al, 2010;Galvez-Contreras et al, 2013).…”

Cell-type profiling in salamanders identifies innovations in vertebrate forebrain evolution

“…For consistency and to facilitate data analysis, we limited data integration to single cells sampled from the same brain regions. We integrated our salamander dataset with data from the telencephalon of the agamid lizard Pogona vitticeps ( 34 , 35 ) and from the pallium of the red-eared slider turtle Trachemys scripta [which also includes cells from the neighboring subpallium ( 7 )]. Clustering of the Seurat integrated data yielded 65 clusters, which we refer to as integrated clusters.…”

“…Using Seurat’s integration pipeline, we generated two integrated datasets using scRNA-seq data from the turtle pallium ( 7 ), the lizard telencephalon ( 35 ), and the mouse cortex and hippocampal formation ( 43 ). Average cluster expression profiles were computed, distances were computed as 1 – cor( x ) (Spearman correlation), and this distance matrix was used for hierarchical clustering with the Ward.D2 method to generate dendrograms (Figs.…”

An entorhinal-like region in food-caching birds

“…19 These nuclei are only partially homologous to the mammalian cortex and contain neurons that differ from the cortex in their embryological origins, morphologies, and molecular signatures. [20][21][22][23] It seems unlikely that the avian brain exactly replicates all details of the mammalian microcircuitry relevant for producing characteristic entorhinal activity patterns, like those of grid cells. [24][25][26][27] This raises the possibility than entorhinal-like circuitry and firing patterns are not generally needed for hippocampal function.…”