Transcriptomic and morphophysiological evidence for a specialized human cortical GABAergic cell type

Abstract

We describe convergent evidence from transcriptomics, morphology and physiology for a specialized GABAergic neuron subtype in human cortex. Using unbiased single nucleus RNA sequencing, we identify ten GABAergic interneuron subtypes with combinatorial gene signatures in human cortical layer 1 and characterize a novel group of human interneurons with anatomical features never described in rodents having large, “rosehip”-like axonal boutons and compact arborization. These rosehip cells show an immunohistochemical profile (GAD1/CCK-positive, CNR1/SST/CALB2/PVALB-negative) matching a single transcriptomically-defined cell type whose specific molecular marker signature is not seen in mouse cortex. Rosehip cells in layer 1 make homotypic gap junctions, predominantly target apical dendritic shafts of layer 3 pyramidal neurons and inhibit backpropagating pyramidal action potentials in microdomains of the dendritic tuft. These cells are therefore positioned for potent local control of distal dendritic computation in cortical pyramidal neurons.

Robust perisomatic GABAergic self-innervation inhibits basket cells in the human and mouse supragranular neocortex

“…However, among various cellular features characterized in humans but not in rodent neocortex (Blazquez-Llorca L et al 2010;Testa-Silva G et al 2010;Molnar G et al 2016;Szegedi V et al 2016;Wang B et al 2016;Beaulieu-Laroche L et al 2018;Boldog E et al 2018;Goriounova NA et al 2018;Kalmbach BE et al 2018;Pruunsild P and H Bading 2019), human neocortical neurons exhibit higher Rm than their rodent counterparts do (Eyal G et al 2016;Poorthuis RB et al 2018). Although our data here showed that human and mouse pvBC input resistance values were not different on average (showing p value of 0.10), human neurons had individual cells showing clearly higher Rm than did those found in any of the mouse pvBCs (Poorthuis RB et al 2018).…”

Single cell transcriptome profiling of the human alcohol-dependent brain

“…A notable limitation of our DE analysis was the sample size of our dataset (7 donors). A small sample size in a single cell genomics study does affect statistical power, but does not preclude the possibility of drawing meaningful inferences of cell type gene expression in the human brain (9,41) . That said, our goal is to increase the sample size for future single cell studies to better identify important expression patterns, particularly for genes that have smaller effect sizes.…”

dotdotdot: an automated approach to quantify multiplex single molecule fluorescent in situ hybridization (smFISH) images in complex tissues

“…While we utilized RNAscope technology for fluorescent probe labeling, non-commercial smFISH technologies have also proven successful in postmortem human brain tissue 4 . However, RNAscope offers a rapid, robust, and universal approach that has now been replicated by several groups for qualitative validation of RNA-seq data in postmortem human brain tissue [3][4][5]18 .…”

“…The widespread generation of single-cell RNA-seq data sets in the neurosciences has fueled a resurgence of smFISH approaches to validate cell type-specific molecular profiles by visualizing individual transcripts at cellular resolution 3,4 . Information from single-cell RNA-seq data has revealed increasingly complex transcriptomic signatures for functionally distinct cell types, including the recently identified Rosehip neurons in cortical layer one 5 and cells with neurogenic potential in the dentate gyrus of the hippocampus 6,7 , such that molecular definition of these cells necessitates combinatorial labeling with multiple probes to confirm both presence and absence of specific transcripts within a spatially-defined context.…”

“…While studies have begun to incorporate multiplex fluorescent approaches in postmortem human brain tissue, no consistent strategy for eliminating, masking, or subtracting lipofuscin autofluorescence has been described 3,5,[18][19][20][21][22] . Some studies have characterized lipofuscin autofluorescence based on size and intensity or custom filter cubes 3,4,21 , but these reports do not document how these approaches impact quantification of fluorescent signals from probe hybridization.…”