Epigenetic programming in the germline is considered to affect development in offspring, but the mechanisms are poorly understood. Embryonic Ectoderm Development (EED) is essential for Polycomb Repressive Complex 2 (PRC2) function, which epigenetically regulates developmental genes in bone. PRC2 is a known regulator of bone stem cell differentiation and is implicated in maintenance of adult bone health. De novo germline mutations in human EED result in Cohen-Gibson syndrome, characterized by overgrowth, accelerated bone aging and skeletal defects. However, EED’s potential to alter oocyte epigenetic programming and consequent offspring development is poorly understood.
To determine the role of EED in oocyte programming, we developed a mouse model in which Eed is specifically deleted in growing oocytes. This model facilitates the production of genetically identical heterozygous offspring from oocytes with differences in their epigenetic heritage. We predicted that offspring from oocytes lacking EED would have impaired bone development, as well as compromised bone maintenance and repair.
Loss of EED in oocytes resulted in the de-repression of 244 genes (FDR<0.05) that were primarily associated with fetal development, including bone formation. MicroCT analyses demonstrated that postnatal day 3 offspring from oocytes lacking EED exhibited greater bone mineral density, increased mineralised bone length (p<0.05, n=8-10) and bone width (p<0.0005, n=8-10). Histological and RNAseq analyses revealed that loss of EED in oocytes resulted in an increased hypertrophic zone (p<0.05, n=8-12) and dysregulation of 312 genes (FDR<0.05) in E17.5 femoral growth plates, indicative of abnormal transcriptional regulation and chondrocyte differentiation in heterozygous experimental offspring, compared to genetically identical heterozygous controls.
Together, these data strongly suggest that altered EED-dependent oocyte programming results in postnatal overgrowth and altered bone development, including similarities to skeletal defects associated with Cohen-Gibson syndrome. This model will be used to identify how inherited epigenetic information controls early life and long-term skeletal development and health.