Isogenic hiPSC models of Turner syndrome development reveal shared roles of inactive X and Y in the human cranial neural crest network.

Viable human aneuploidy can be challenging to model in rodents due to syntenic boundaries or primate-specific biology. Human monosomy-X (45,X) causes Turner syndrome (TS), altering craniofacial, skeletal, endocrine, and cardiovascular development, which in contrast remain unaffected in X-monosomic mice. To learn how monosomy-X may impact embryonic development, we turned to 45,X and isogenic euploid human induced pluripotent stem cells (hiPSCs) from male and female mosaic donors. Because the neural crest (NC) is hypothesized to give rise to craniofacial and cardiovascular changes in TS, we assessed differential expression of hiPSC-derived anterior NC cells (NCCs). Across three independent isogenic panels, 45,X NCCs show impaired acquisition of PAX7SOX10 markers and disrupted expression of other NCC-specific genes relative to isogenic euploid controls. Additionally, 45,X NCCs increase cholesterol biosynthesis genes while reducing transcripts with 5' terminal oligopyrimidine (TOP) motifs, including those of ribosomal and nuclear-encoded mitochondrial proteins. Such metabolic pathways are also over-represented in weighted co-expression modules that are preserved in monogenic neurocristopathy and reflect 28% of all TS-associated terms of the human phenotype ontology. We demonstrate that 45,X NCCs reduce protein synthesis despite activation of mammalian target of rapamycin (mTOR) but are partially rescued by mild mTOR suppression. Our analysis identifies specific sex-linked genes that are expressed from two copies in euploid males and females alike and qualify as candidate haploinsufficient drivers of TS phenotypes in NC-derived lineages. This study demonstrates that isogenic hiPSC-derived NCC panels representing monosomy-X can serve as powerful models of early NC development in TS and inform new hypotheses toward its etiology.