Human neocortical expansion involves glutamatergic neuron diversification

Abstract

The neocortex is disproportionately expanded in human compared with mouse1,2, both in its total volume relative to subcortical structures and in the proportion occupied by supragranular layers composed of neurons that selectively make connections within the neocortex and with other telencephalic structures. Single-cell transcriptomic analyses of human and mouse neocortex show an increased diversity of glutamatergic neuron types in supragranular layers in human neocortex and pronounced gradients as a function of cortical depth3. Here, to probe the functional and anatomical correlates of this transcriptomic diversity, we developed a robust platform combining patch clamp recording, biocytin staining and single-cell RNA-sequencing (Patch-seq) to examine neurosurgically resected human tissues. We demonstrate a strong correspondence between morphological, physiological and transcriptomic phenotypes of five human glutamatergic supragranular neuron types. These were enriched in but not restricted to layers, with one type varying continuously in all phenotypes across layers 2 and 3. The deep portion of layer 3 contained highly distinctive cell types, two of which express a neurofilament protein that labels long-range projection neurons in primates that are selectively depleted in Alzheimer’s disease4,5. Together, these results demonstrate the explanatory power of transcriptomic cell-type classification, provide a structural underpinning for increased complexity of cortical function in humans, and implicate discrete transcriptomic neuron types as selectively vulnerable in disease.

Single-cell multiomics atlas of organoid development uncovers longitudinal molecular programs of cellular diversification of the human cerebral cortex

“…(B) UMAP displaying the five transcriptional subtypes of adult CPN described in (Hodge et al ., 2019; Berg et al ., 2021). …”

“…We define a lineage map that reveals the molecular logic underlying cell specification across the main human cortical lineages, and identify species-specific differences in lineage-associated genes and in transcription factors mediating fate specification in the human cortex. Notably, we discover that the recently-described transcriptional diversity in adult human callosal projection neurons (CPN) (Berg et al ., 2021), a population that has undergone unusual expansion in the human cerebral cortex, emerges at early stages of corticogenesis, providing first demonstration of an early developmental appearance of this human-specific cortical feature.…”

A multimodal cell census and atlas of the mammalian primary motor cortex

“…In these studies, we derive a cross-species consensus molecular taxonomy of cell types using scRNA-seq or single-nucleus RNA sequencing (snRNA-seq), DNA methylation and chromatin accessibility data [37][38][39][40] . In mouse, we map the spatial cellular organization by multiplexed error-robust fluorescence in situ hybridization (MERFISH) 41 , characterize morphological and electrophysiological properties by multimodal profiling using patch clamp recording, biocytin staining and scRNA-seq (Patch-seq) 42,43 , describe the cellular input-output wiring diagrams by anterograde and retrograde tracing 44 , identify glutamatergic neuron axon projection patterns by Epi-retro-seq 45 , Retro-MERFISH 41 and single-neuron complete morphology reconstruction 46 , and describe transgenic driver lines targeting glutamatergic cell types on the basis of marker genes and lineages 47 . Finally, we integrate this information into a cohesive description of cell types in MOp.…”

Building on a Solid Foundation: Adding Relevance and Reproducibility to Neurological Modeling Using Human Pluripotent Stem Cells

“…The brain is the most complex organ in the human body, estimated to contain over 85 billion neurons and a similar number of non-neuronal cells (Azevedo et al, 2009 ). Specialized neuron subtypes continue to be identified and characterized at an increasing rate (Chen et al, 2017 ; Zhong et al, 2018 ; Hodge et al, 2019 ; Ximerakis et al, 2019 ; Polepalli et al, 2020 ; Bakken et al, 2021 ; Berg et al, 2021 ). The diverse non-neural populations that populate our brains include astrocytes, oligodendrocytes, neural stem and progenitor cell subtypes, and those with mesenchymal (microglia), epithelial (choroid plexus) and endothelial (vasculature) origins.…”

“…Additionally, the mouse brain lacks certain defined structures and cell types that are found in humans. These include a greater number of glutamatergic neuron subtypes in the supragranular region of the human cortex (Hodge et al, 2019 ; Berg et al, 2021 ) and the human outer subventricular zone (oSVZ). The oSVZ is populated with basal radial glia cells, a neocortical stem cell type important for neuronal expansion and cortical folding in gyrencephalic species; in line with the expanded oSVZ in humans, basal radial glia are abundant in humans and rare in mice (Pollen et al, 2015 ).…”