Differential susceptibility of male and female germ cells to glucocorticoid-mediated signaling [scRNAseq_Female]
While physiologic stress has long been known to impair mammalian reproductive capacity through hormonal dysregulation, mounting evidence now suggests that stress experienced prior to or during gestation may also negatively impact the health of future offspring. Rodent models of gestational physiologic stress can induce neurologic and behavioral phenotypes that persist for up to three generations, suggesting that stress signals can induce lasting epigenetic changes in the germline. Treatment with glucocorticoid stress hormones is sufficient to recapitulate the transgenerational phenotypes seen in physiologic stress models. These hormones are known to bind and activate the glucocorticoid receptor (GR), a ligand-inducible transcription factor, thus implicating GR-mediated signaling as a potential contributor to the transgenerational inheritance of stress-induced phenotypes. Here we demonstrate dynamic spatiotemporal regulation of GR expression in the mouse germline, showing expression in the fetal oocyte as well as the perinatal and adult spermatogonia. Functionally, we find that fetal oocytes are intrinsically buffered against changes in GR signaling, as neither genetic deletion of GR nor GR agonism with dexamethasone altered the transcriptional landscape or the progression of fetal oocytes through meiosis. In contrast, our studies revealed that the male germline is susceptible to glucocorticoid-mediated signaling, specifically by regulating RNA splicing within the spermatogonia, although this does not abrogate fertility. Together, our work suggests a sexually dimorphic function for GR in the germline, and represents an important step towards understanding the mechanisms by which stress can modulate the transmission of genetic information through the germline. Overall design: To interrogate the role of the glucocorticoid receptor (GR) in female germ cells, we performed single cell RNA-seq on germ cells following genetic deletion of GR. To generate the GR deletion allele, mouse strain Nr3c1tm1.1Jda harboring a floxed allele of GR exon 3 was crossed to ß-actin cre mice (Tmem163Tg(ACTB-cre)2Mrt) to generate a heterozygous deletion of GR. Mice with heterozygous deletion of GR were crossed to OCT4-GFP mice (Tg(Pou5f1-EGFP)2Mnn) to facilitate germ cell labeling. As the GR deletion allele is homozygous lethal at birth, mice were maintained as heterozygotes, and crossed to each other to generate embryos with homozygous deletion of GR for the experiment. To enrich for germ cells, fetal ovaries from GR deletion and WT controls were collected at E15.5, pooled according to genotype (n=2 GR deletion embryos, n=4 WT embryos), and were digested and FACS sorted for the OCT4-GFP transgene. OCT4-GFP positive germ cells were mixed back in with sorted OCT4-GFP negative somatic cells at a ratio of 60:40, and samples were submitted for single cell RNA-seq using the 10X Illumina platform.