Moon, J. E. | Search bioRxiv

bioRxiv2025

Selective chr21 homolog silencing reveals polymorphisms influence the epigenetic silencing and functional dosage of RWDD2B

Polymorphisms that affect chr21 gene expression have significance for both variable severity in Down syndrome and common multifactorial conditions. Results here demonstrate "selective homolog silencing" in cells from even one individual can provide a valuable complement to large studies. In trisomic iPSC subclones that silence different chr21 homologs (via XIST-based silencing), we discovered unusually large, homolog-specific, differences in RWDD2B in iPSCs, cortical organoids and endothelial cells. RNA FISH showed RWDD2B transcription almost entirely from the H1 homolog, correlated with CpG promoter methylation differences. Polymorphisms different on H1 versus H2/H3 had strongest eQTLs in GTEx, especially in brain. Collective results indicate RWDD2B functional dosage is more frequently disconnected from copy number even compared to neighboring genes. RWDD2B function is unknown, but nearby methyl-eQTLs are implicated in osteoarthritis, and potential roles in inflammation or immune response merit consideration. This study has significance for RWDD2B regulation and demonstrates a cell-based methodology to study polymorphisms.

genetics↗

bioRxiv2022

Chromosome silencing in vitro reveals trisomy 21 causes cell-autonomous deficits in angiogenesis and early dysregulation in Notch signaling

Despite the prevalence and clinical importance of Down syndrome, little is known as to the specific cell pathologies that underlie this multi-system disorder. To understand which cell types and pathways are more directly impacted by trisomy 21, we used an inducible-XIST system to silence the extra chromosome 21 in a panel of patient-derived iPSCs. Transcriptomic analysis showed significant dysregulation of Notch signaling occurring as early as pluripotent stem cells, potentially impacting programming of multiple cell-types. Unbiased analysis from iPSCs revealed prominent dysregulation in two major cell type processes: neurogenesis and angiogenesis. Angiogenesis is important for many systems impacted in Down syndrome but has been understudied; therefore, we focused on investigating whether trisomy 21 impacts endothelial cells. An in vitro assay for microvasculature formation used in a tightly controlled system reveals a novel cellular pathology involving delays in angiogenic response during tube formation. Results demonstrate that this is a cell-autonomous effect of trisomy 21, and transcriptomic analysis of differentiated endothelial cells shows deficits in known angiogenesis regulators. This study reveals a major unknown cell pathology caused by trisomy 21 and highlights the importance of endothelial cell function for Down syndrome comorbidities, with wide reaching implications for development and disease progression.

developmental biology↗