<p>Excess gene dosage from human chromosome 21 (HSA21), due to trisomy or translocation of HSA21 material, causes Down syndrome (DS). We derived trisomy 21 (T21) induced pluripotent stem cells (iPSCs) alongside otherwise isogenic euploid controls from mosaic DS fibroblasts (GM00260, first described in Lubiniecki et al., PMID: <a href="https://pubmed.ncbi.nlm.nih.gov/225951/">225951</a>) of the NIGMS genetic cell repository, to enable analysis of whole-chromosomal and individual gene dosage imbalance in the context of in vitro models of DS development. Virtual karyotyping (by Infinium CytoSNP-850k), and phased genotyping (by linked-read whole-genome sequencing) of the resulting iPSC lines provide a deeply-characterized genomic platform for dissection of HSA21 gene dosage. We apply this highly unique resource to allelic analysis of mRNA sequencing of iPSCs and differentiated neural lineages, and demonstrate its utility in the context of inducible HSA21 dosage compensation. To this end, we equipped one distinct HSA21 copy with a doxycycline-inducible XIST transgene, which endogenously silences one X in 46,XX females. Standard and allele-specific RNA-seq analysis confirms mono-allelic T21 silencing to be virtually complete and irreversible, further supported by DNA methylation data (Infinium methylEPIC). This full-length HSA21 map of phased single-nucleotide and insertion/deletion variants enables allele-specific applications for gene-level dissection T21 dosage effects. Because our XIST remains inducible in post-mitotic T21 neurons and astrocytes, we perform single-nuclei RNA-seq to demonstrate XIST efficiently represses genes even after terminal differentiation.</p>

Trisomy 21 Dosage Compensation Map (T21DoCoMap)

SV40 T-antigen expression in cultured fibroblasts from patients with Down syndrome and their parents.

A dynamic in vitro model of Down syndrome neurogenesis with trisomy 21 gene dosage correction