BRN2 as a key gene drives the early primate telencephalon development

Abstract

Evolutionary mutations in primate-specific genes drove primate cortex expansion. However, whether conserved genes with previously unidentified functions also play a key role in primate brain expansion remains unknown. Here, we focus on BRN2 ( POU3F2 ), a gene encoding a neural transcription factor commonly expressed in both primates and mice. Compared to the limited effects on mouse brain development, BRN2 biallelic knockout in cynomolgus monkeys ( Macaca fascicularis ) is lethal before midgestation. Histology analysis and single-cell transcriptome show that BRN2 deficiency decreases RGC expansion, induces precocious differentiation, and alters the trajectory of neurogenesis in the telencephalon. BRN2 , serving as an upstream factor, controls specification and differentiation of ganglionic eminences. In addition, we identified the conserved function of BRN2 in cynomolgus monkeys to human RGCs. BRN2 may function by directly regulating SOX2 and STAT3 and maintaining HOPX . Our findings reveal a previously unknown mechanism that BRN2 , a conserved gene, drives early primate telencephalon development by gaining novel mechanistic functions.

Brain and Organoid Manifold Alignment (BOMA), a machine learning framework for comparative gene expression analysis across brains and organoids

“…These findings were confirmed with immunofluorescent staining of human organoids of SATB2 (Figure 6C, <1.5% cells) and PSMB5 (Figure 6I, ∼10% of cells) across 8-weeks, 10.5-weeks, and 14-weeks differentiation time points corresponding to segments 7, 8, and 9, respectively (Figure 6C and 6I). Also, POU3F2 , encoding a transcription factor important for primate radial glia expansion and differentiation 47 , displayed no expression throughout organoids maturation by BOMA (Figure 6A), and indeed it was found expressing in a small number of cells (∼3%) in organoids by immunostaining (Figure 6F).…”

BRN1/2 Function in Neocortical Size Determination and Microcephaly

“…In BRN2KO monkeys, the neurogenic behavior of cortical progenitors is similarly altered as in Brn1/2-cKO mice 36 . To test if the mechanisms by which BRN1/2 regulate progenitor behavior are evolutionary conserved, we first inhibited BRN1/2 activity in wild-type ferrets at E35 by IUE with pCAG-Brn-DBD-EnR, a dominant negative inhibitor of BRN1/2 function (Fig.…”

“…While our findings provide evidence for an evolutionary conserved role for BRN1/2 regulation of transcriptional programs that control progenitor behavior, it remains to be established to what extent the function of these transcriptional regulators has been modified during brain evolution to produce differences in brain size. For example, disruption of BRN2 function alone affects cortical development in monkeys 36 , but not in mice 18,19 , suggesting that redundancy of BRN1 and BRN2 function is not universally conserved. In addition, recent studies have shown that during evolution, enhancers that control neuronal gene expression have been altered by mutations that affect predominantly binding sites for a limited set of transcription factors, including BRN1/2 50 .…”

“…h’, Total OLIG2 + cells in the electroporated somatosensory cortex (n=4 CT, n=5 Brn-Enr ferrets; unpaired t - test). i, ScRNAseq DATA from E36 cortex of control and BRN2 KO cynomolgus monkey 36 re-analyzed using the same pipeline we used for the analysis in mice. j , k, UMAP of scRNAseq from control and BRN2 KO cortices by genotype (j) and cell type (k).…”

“…Next, we analyzed available raw scRNAseq data from BRN2 KO monkeys at E36 36 using identical criteria as employed in our analysis of scRNAseq from mice (Fig. 4i-k).…”