The X-Linked Intellectual Disability gene, ZDHHC9, is important for oligodendrocyte maturation and myelin formation
Two percent of all patients with X-linked intellectual disability (XLID) exhibit loss-of-function mutations in the palmitoylating enzyme, ZDHHC9. One of the main anatomical deficits observed in these patients is a decrease in corpus callosum volume and a disruption of white matter integrity. We demonstrated that ablation of Zdhhc9 in mice substantially impairs the maturation of oligodendrocytes, resulting in fewer mature, myelinating oligodendrocytes, higher numbers of oligodendrocyte progenitor cells and a decrease in the density of myelinated axons. Ultrastructural analysis of the remaining myelinated axons in the corpus callosum revealed further disruptions in myelin integrity. RNA sequencing and proteomic analyses revealed a concomitant decrease in the expression of genes and proteins involved in lipid metabolism, cholesterol synthesis and myelin compaction. These results reveal a previously underappreciated and fundamental role for ZDHHC9 and protein palmitoylation in regulating oligodendrocyte differentiation and myelinogenesis and provide mechanistic insights into the deficits observed in white matter volume in patients with mutations in ZDHHC9. Overall design: Wild-type and Zdhhc9 knockdown corpus callosum and optic nerve from mice were studied via RNA-seq using between 4 and 6 replicates for each tissue-genotype combination.