Altered Sperm H3K27me3 Disrupts Offspring Skeletal Structure, Craniofacial Development, and Prenatal Viability

Authors: Tia M. Hoisington¹; Mustika Rahmawati¹; Amanda Brown¹; Nathan Law¹

1. School of Molecular Biosciences, Washington State University, Pullman, USA

Abstract Text:

During sperm production, DNA packaged within germ cells undergoes a major remodeling in which histones are replaced with protamines, which protect the paternal genome from damage. However, in mature sperm, histones are retained in approximately 1-10% of the mouse genome and 4-15% of the human genome. Among histones retained in sperm, histone H3 lysine 27 trimethylation (H3K27me3) is a canonical repressive epigenetic mark that is broadly deposited in the sperm epigenome. However, the functional significance of H3K27me3 in sperm and the relationship between other epigenetic marks in the male germline remains unclear. To address this gap in knowledge, we generated a novel Cre-driven mouse model that overexpresses (OE) the lysine demethylase Kdm6b to study the impact of diminished H3K27me3 on post-meiotic spermatogenesis and embryo development. Outcomes of sperm analyses indicate that Kdm6b OE does not impact sperm production, motility, morphology, or fertilization. Strikingly, however, ongoing studies indicate that Kdm6b OE sires have increased prenatal death. Based on developmental landmarks, including retinal pigmentation, prenatal death occurs primarily in mid- to late-gestation. While many internal organ systems, such as the liver and heart, appear intact in offspring from Kdm6b OE sires, many offspring lack intact brain tissue and display deformed craniofacial structures. Additionally, we observed disorganized vertebral columns that deviate from traditional linear formation and lack a distinct separation from the cranial cavity, suggesting abnormalities in embryo patterning. These ongoing studies functionally demonstrate that sperm H3K27me3 is critical for embryo development. Furthermore, our findings provide a fundamental understanding of the paternal epigenetic contribution to fetal development and post-implantation loss.