Single substitution in H3.3G34 alters DNMT3A recruitment to cause progressive neurodegeneration

Germline histone H3.3 amino acid substitutions, including H3.3G34R/V, cause severe neurodevelopmental syndromes. To understand how these mutations impact brain development, we generated H3.3G34R/V/W knock-in mice and identified strikingly distinct developmental defects for each mutation. H3.3G34R-mutants exhibited progressive microcephaly and neurodegeneration, with abnormal accumulation of disease-associated microglia and concurrent neuronal depletion. G34R severely decreased H3K36me2 on the mutant H3.3 tail, impairing recruitment of DNA methyltransferase DNMT3A and its redistribution on chromatin. These changes were concurrent with sustained expression of complement and other innate immune genes possibly through loss of non-CG (CH) methylation and silencing of neuronal gene promoters through aberrant CG methylation. Complement expression in G34R brains may lead to neuroinflammation possibly accounting for progressive neurodegeneration. Our study reveals that H3.3G34-substitutions have differential impact on the epigenome, which underlie the diverse phenotypes observed, and uncovers potential roles for H3K36me2 and DNMT3A-dependent CH-methylation in modulating synaptic pruning and neuroinflammation in post-natal brains. [Display omitted] •Germline H3.3G34R/V/W mutations cause distinct developmental defects•G34R mice show severe neurological deficits, microcephaly, and neurodegeneration•G34R decreased H3K36me2 and impairing recruitment of DNA methyltransferase DNMT3A•DNA methylation dysregulation is associated with immune activation & neuronal loss A study exploring the effect of human germline histone H3.3 amino acid mutations in mice provides insights into their differential impact on the epigenome as well as roles for DNA methylation dysregulation in modulating synaptic pruning and neuroinflammation in post-natal brains.