UCLA

The mechanisms by which sex differences in the mammalian brain arise are poorly understood, but are influenced by a combination of underlying genetic differences and gonadal hormone exposure. Using a mouse embryonic neural stem cell (eNSC) model to understand early events contributing to sexually dimorphic brain development, we identified novel interactions between chromosomal sex and hormonal exposure that are instrumental to early brain sex differences. RNA-sequencing identified 103 transcripts that were differentially expressed between XX and XY eNSCs at baseline (FDR=0.10). Treatment with testosterone-propionate (TP) reveals sex-specific gene expression changes, causing 2854 and 792 transcripts to become differentially expressed on XX and XY genetic backgrounds respectively. These findings indicate that testosterone exposure on XX cells have a more robust effect with regards to altering gene expression. It was also found that by exposing XX eNSCs to TP, 42% (43/103) of the original 103 basal sex differences that existed became masculinized and shifted towards a XY typical gene expression pattern. We also determined that 25% (26/103) of basal sex differences were actually feminized in an XY background post-TP. These alteration in gene expression post-TP exposure were determine to require functional androgen receptor (AR), as AR knockout (ARKO) eNSCs did not show differential expression of select genes in the presence of TP. Within the TP responsive transcripts, there was enrichment for genes which function as epigenetic regulators that affect both histone modifications and DNA methylation patterning, specifically Tet proteins, known to function as a DNA demethylases. We observed that TP caused a global decrease in 5-methylcytosine abundance in both sexes, a transmissible effect that was maintained in cellular progeny. Like gene expression, alteration in DNA methylation function downstream of AR activation, with ARKO lines showing no significant androgen induced DNA de-methylation. Additionally, we determined that TP was associated with residue-specific alterations in acetylation of histone tails. Collectively, these findings highlight an unknown component of androgen action on cells within the developmental CNS, and contribute to a novel mechanism of action by which early hormonal organization is initiated and maintained.