Analysis of astrocyte precursor cells in Down syndrome (ChIP-seq)

Innovative model system for studying the biology of Down syndrome (DS) has been developed using DS-specific iPSCs and human X-inactivation gene, XIST. In this cell line, XIST was inserted into one copy of chromosome 21 in DS iPSCs, and a long noncoding RNA induced a series of chromatin modifications that stably silence gene transcription across whole chromosome in cis. Given that expression of XIST RNA is regulated by tetracycline inducible system, this genome silencing technology enables us to investigate the correlation among genomic expression changes, the accumulation of H3K27me3 and cellular phenotypes in DS, without the limitation caused by the transcriptional heterogeneity and differences among cell lines. Analysis of human brains with DS revealed that astrocytes are more abundant and morphologically more mature than those of age-matched controls. Moreover, astrocytes from DS mouse models indeed exhibited reduced activities of cholinergic neurons, altered calcium homeostasis and defective regulation of cell proliferation, raising the possibility of a direct contribution of astrocytes to DS pathophysiology. To investigate the molecular feature of DS pathology, we focused on the iPSC-derived astrocyte precursor cell (APC) proliferation and its key regulator. Taking advantage of XIST-induced chromosome silencing technique, comparative analysis of ChIP-seq data of H3K27me3 and proliferative phenotypes on common genetic background was performed. Dox-removal lines were also used to perform the assays.