FOXP1 orchestrates neurogenesis in human cortical basal radial glial cells

Abstract

During cortical development, human basal radial glial cells (bRGCs) are highly capable of sustained self-renewal and neurogenesis. Selective pressures on this cell type may have contributed to the evolution of the human neocortex, leading to an increase in cortical size. bRGCs have enriched expression for Forkhead Box P1 (FOXP1), a transcription factor implicated in neurodevelopmental disorders such as autism spectrum disorder. However, the cell type-specific roles of FOXP1 in bRGCs during cortical development remain unexplored. Here, we examine the requirement for FOXP1 gene expression regulation underlying the production of bRGCs using human brain organoids. We examine a developmental time point when FOXP1 expression is highest in the cortical progenitors, and the bRGCs, in particular, begin to actively produce neurons. With the loss of FOXP1, we show a reduction in the number of bRGCs, as well as reduced proliferation and differentiation of the remaining bRGCs, all of which lead to reduced numbers of excitatory cortical neurons over time. Using single-nuclei RNA sequencing and cell trajectory analysis, we uncover a role for FOXP1 in directing cortical progenitor proliferation and differentiation by regulating key signaling pathways related to neurogenesis and neurodevelopmental disorders. Together, these results demonstrate that FOXP1 regulates human-specific features in early cortical development.

A foundational atlas of autism protein interactions reveals molecular convergence

“…Together, our results suggest that expression of the FOXP1 R513H allele during human forebrain differentiation alters gene regulatory relationships involving FOXP1 and FOXP4 transcription factors. While our scRNA-seq data did not suggest major differences in progenitor cell abundance, we detected a modest, but statistically significant decrease in the abundance of PAX6 positive cells, consistent with the proposed role for FOXP1 in human radial glia development 130 and with findings from FOXP1 knockout organoids 133 . In addition, our findings implicate the FOXP1 R513H allele in altered differentiation of deep cortical layer and subplate neurons, which we confirmed by immunostaining for TBR1 ( Figures 8J,K , S8K ).…”

“…Examining the impact of FOXP1 R513H/WT in forebrain organoids revealed several phenotypic characteristics, including reduced abundance of radial glia, mirroring the effects of null alleles 133 .…”

“…Examining the impact of FOXP1 R513H/WT in forebrain organoids revealed several phenotypic characteristics, including reduced abundance of radial glia, mirroring the effects of null alleles 133 . Interestingly, no major differences in deep cortical layer neuron differentiation were observed in organoids with homozygous null mutations in FOXP1, while heterozygous FOXP1 R513H/WT organoids exhibited specific transcriptional dysregulation related to the differentiation of deep cortical layer neurons.…”

“…FOXP1 is a forkhead-box (FOX) family transcription factor that is important in the early development of multiple organ systems, including the brain [124][125][126][127][128][129][130][131][132][133] . The transcriptional activity of FOXP1 is regulated by homo-and heterodimerization with other FOX proteins 134,135 .…”

Cell type specific roles of FOXP1 during early neocortical murine development

“…Neurons had robust association with ASD-relevant genes in terms of both DEGs and DARs. Though we anticipated enrichment between neuronal DEGs and ASD genes based on previous work in both postnatal mice and human brain organoids (Araujo et al 2015; Park et al 2023), we asked whether neural progenitor cells (NPCs) would also share this enrichment since this has not been previously investigated in Foxp1 cKOs. Both aRGs and IPs also exhibit significant enrichment with ASD genes (Fig.…”