EPIGENETIC AND FUNCTIONAL ASSESSMENT OF ENHANCEROPATHIES ACROSS HUMAN MODELS: FOCUS ON GABRIELE-DE VRIES SYNDROME

Yin Yang 1 (YY1) is a ubiquitous zinc finger transcription factor (TF) that occupies active enhancers and promoters contributing to physical interactions between these regions via DNA looping. Increasing evidence shows that disruption of non-coding regions such as enhancers is prevalent across different neurodevelopmental disorders (NDDs) with intellectual disability (ID) features. Indeed, YY1 haploinsufficiency causes a NDD with ID, named Gabriele-de Vries syndrome (GADEVS). Although it is known that YY1 controls the expression of a dazzling list of genes and influences various cellular processes in numerous cell types, the impact of this TF in the neurodevelopment of the human cortex is yet to be unraveled. By taking advantage of disease-modeling as a tool to investigate the pathogenesis of GADEVS across different time points and tissues we gathered new insights about how YY1 haploinsufficiency exerts such a dramatic phenotype in individuals carrying mutations. We reprogrammed patient-derived and healthy somatic cells into induced-pluripotent stem cells (iPSCs) and observed, already at the pluripotent stage, a major transcriptional dysregulation. Moreover, since YY1-mutated patients exhibit ID features, we differentiated our cohort of iPSCs into cortical neurons as well organoids and were able to capture stage-specific striking features, not only at the transcriptomic level, but also structural and compartmentalization impairments. Of note, YY1-mutated neurons displayed synaptic disparities, sufficient to induce astrogliosis-like features in surrounding astrocytes, both shown to be critical for proper brain function and plasticity forms in the CNS. Instead, in cortical organoids we recapitulated features of abnormal ventricle formation, pathological hallmarks observed in GADEVS patients and mice models followed by ID and developmental delay. This study showed, for the first time, the molecular signatures that possibly lead to cognitive defects in human patients and provide the first solid foundation for the development of therapeutic strategies and drug screening in the future.