24.3 NEURAL TARGET GENES OF ESTROGEN RECEPTOR ALPHA SPECIFY SEX DIFFERENCES IN THE BRAIN

Abstract

The “female protective effect” (FPE) theory suggests that females with loss-of-function mutations in autism spectrum disorder (ASD)-associated genes are resistant to developing ASD symptoms. However, it has been challenging to identify candidate pathways that could promote an FPE, as there is minimal information on sex differences in neurodevelopmental trajectories. In rodents, estrogen receptor alpha (ERα) is necessary and sufficient for sex differences in neural connectivity and behavior, but the neural genes regulated by this transcription factor had not been described. We employed CUT&RUN sequencing to identify direct ERα genomic binding sites in the brains of female and male mice. We performed RNA-seq and ATAC-seq specifically within ERα+ neurons within the bed nucleus of the stria terminalis (BNST), a sexually dimorphic brain region that regulates social and motivated behaviors, to associate ERα binding with gene regulation. We assessed snRNA-seq data from the BNST of both sexes to identify sex differences both in transcripts within a cell type and in cell types and correlated these findings with ERα occupancy. ERα directly binds neurodevelopmental genes, including several strong ASD candidate loci. Sex differences in gene expression in the brain occur exclusively in cells that express ERα. ERα regulates a male-biased gene expression program that initiates in early life and cooperates with the transcription factor Nfix to specify identity of a male-biased inhibitory neuronal population. We identify an estrogen-driven transcriptional strategy for brain masculinization. We anticipate that ERα target genes and loci contribute to susceptibility or resilience to developing ASD and that other genetic or environmental factors can intersect with mutations in these loci to produce sex-specific outcomes.