Multipotent radial glia progenitors and fate-restricted intermediate progenitors sequentially generate diverse cortical interneuron types

Abstract

GABAergic interneurons deploy numerous inhibitory mechanisms that regulate cortical circuit operation, but the developmental programs that generate diverse interneuron types remain not well understood. We carried out a comprehensive genetic fate mapping of the radial glial progenitors (RGs) and intermediate progenitors (IP) in the medial ganglionic eminence (MGE). We reveal that Nkx2.1 + RGs are multipotent and mediate two consecutive waves of neurogenesis, each sequentially generating different sets of interneuron types that laminate the neocortex in an inside-out-inside order. The first wave is restricted to the caudal MGE, has limited neurogenic capacity, and involves mostly apical IPs.The second wave initiates throughout the MGE and features a large set of fate-restricted basal IPs that amplify and diversify interneurons. Chandelier cells are generated toward the end of each wave and laminate in an outside-in order. Therefore, separate pools of multipotent RGs deploy temporal cohorts of IPs to sequentially generate diverse interneuron types.

Parallel RNA and DNA analysis after deep sequencing (PRDD-seq) reveals cell type-specific lineage patterns in human brain

“…Previous studies cataloging interneurons in mouse and human have suggested that MGE-derived inhibitory neuron subtypes (SST+ and PVALB+) are enriched in infragranular cortical layers, while CGE-derived interneuron subtypes (LAMP5/PAX6+, VIP+) tend to occupy upper cortical layers preferentially (5,42,43), and thus our mapping of PRDD-seq cells onto scRNAseq reflected these patterns. Birthdating analyses in mice and nonhuman primates have reached contradictory conclusions about whether inhibitory neurons follow inside-out patterns of generation similar to excitatory neurons (44,45), although recent analyses in mice suggest that previous contradictions may reflect the convolution of multiple patterns of generation that may be subtype specific (46). We found that MGEderived pPVALB+ subtype neurons, enriched in layers IV to VI, showed, if anything, a trend for the latest-generated neurons to show markers of deeper layers ( Fig.…”

Transcriptional profiling of sequentially generated septal neuron fates

“…Our molecular profiling data suggest that the temporally defined molecular states of septal progenitors and neuronal precursors correlate with the production of specific cell fates. To better understand how birthdate affects the specification of neurons derived from the septal eminence, we used an intersectional approach based on Ascl1 expression by fate-restricted neurogenic progenitors within the Nkx2.1 lineage ( Kelly et al, 2018 ; Kelly et al, 2019 ; Figure 5A ). We combined the Nkx2.1-Flp driver mouse line with a tamoxifen (TMX)-inducible Ascl1-CreER T2 line and the intersectional Ai65 reporter line, which expresses the fluorescent protein tdTomato in a Cre- and Flp-dependent manner ( Figure 5B ).…”

“…We combined the Nkx2.1-Flp driver mouse line with a tamoxifen (TMX)-inducible Ascl1-CreER T2 line and the intersectional Ai65 reporter line, which expresses the fluorescent protein tdTomato in a Cre- and Flp-dependent manner ( Figure 5B ). Administration of tamoxifen causes the expression of tdTomato in cells with a developmental history of Nkx2.1 expression that are undergoing a peak of Ascl1 expression, leading to a neurogenic division ( Kelly et al, 2019 ). We administered tamoxifen to timed-pregnant dams at four embryonic timepoints spanning the neurogenic period (E10, E12, E14, and E16) and collected the brains of their progeny at P30 when development of the septum is complete ( Figure 5C ).…”

Parallel RNA and DNA analysis after Deep-sequencing (PRDD-seq) reveals cell type specific lineage patterns in human brain

“…Previous studies cataloging interneurons in mouse and human have suggested that MGE-derived inhibitory neuron subtypes (SST+ and PVALB+) are enriched in infragranular cortical layers, while CGE-derived interneuron subtypes (LAMP5/PAX6+, VIP+) tend to occupy upper cortical layers preferentially (5, 42, 43) and thus our mapping of PRDD-seq cells onto scRNAseq reflected these patterns. Birthdating analyses in mice and non-human primates have reached contradictory conclusions about whether inhibitory neurons follow inside-out patterns of generation similar to excitatory neurons (44, 45), though recent analyses in mice suggest that previous contradictions may reflect the convolution of multiple patterns of generation that may be subtype specific (46). We found that MGE-derived pPVALB+ subtype neurons, enriched in layer IV-VI, showed if anything a trend for the latest-generated neurons to show markers of deeper layers (Fig.…”