X-Chromosome Inactivation in Rett Syndrome Human Induced Pluripotent Stem Cells

Abstract

Rett syndrome (RTT) is a neurodevelopmental disorder that affects girls due primarily to heterozygous mutations in the X-linked gene encoding methyl-CpG binding protein 2 (MECP2). Random X-chromosome inactivation (XCI) results in cellular mosaicism in which some cells express wild-type (WT) MECP2 while other cells express mutant MECP2. The generation of patient-specific human induced pluripotent stem cells (hiPSCs) facilitates the production of RTT-hiPSC-derived neurons in vitro to investigate disease mechanisms and identify novel drug treatments. The generation of RTT-hiPSCs has been reported by many laboratories, however, the XCI status of RTT-hiPSCs has been inconsistent. Some report RTT-hiPSCs retain the inactive X-chromosome (post-XCI) of the founder somatic cell allowing isogenic RTT-hiPSCs that express only the WT or mutant MECP2 allele to be isolated from the same patient. Post-XCI RTT-hiPSCs-derived neurons retain this allele-specific expression pattern of WT or mutant MECP2. Conversely, others report RTT-hiPSCs in which the inactive X-chromosome of the founder somatic cell reactivates (pre-XCI) upon reprogramming into RTT-hiPSCs. Pre-XCI RTT-hiPSC-derived neurons exhibit random XCI resulting in cellular mosaicism with respect to WT and mutant MECP2 expression. Here we review and attempt to interpret the inconsistencies in XCI status of RTT-hiPSCs generated to date by comparison to other pluripotent systems in vitro and in vivo and the methods used to analyze XCI. Finally, we discuss the relative strengths and weaknesses of post- and pre-XCI hiPSCs in the context of RTT, and other X-linked and autosomal disorders for translational medicine.

Electrophysiological abnormalities in induced pluripotent stem cell‐derived cardiomyocytes generated from Duchenne muscular dystrophy patients

“…During reprogramming, X chromosome status is destined to be one of the following three options: (1) conserved inactivation pattern of the originating somatic cell (XaXi); (2) reactivation of the inactive X chromosome (XaXa); (3) erosion of XCI (XaXe). [12][13][14][15][16][17][18] Considering XIST expression does not sufficiently indicate X chromosome status, and based on the NGS dystrophin expression analyses, a likely possibility is that a mixed population was established during reprogramming and each differentiation. 17,18 In this scenario, DMD female iPSC-CMs can be divided to two sub-populations: (1) cells expressing the WT allele, and (2) cells expressing the mutated allele.…”

Pluripotent stem cells as a model to study non-coding RNAs function in human neurogenesis

“…Most forms of RS are due to a loss of function mutation in the transcriptional repressor MeCP2 (methyl CpG binding protein 2; Ravn et al, 2011). RS iPSC replicate some prototypical features found in animal models including decreased neuronal soma size, neuritic atrophy and decreased efficiency of glutamatergic synapses (Marchetto et al, 2010; Kim et al, 2011c; Cheung et al, 2012). Disruption of MeCP2 gene in mice leads to the dysregulation of a set of miRNA potentially of influence in neurogenesis including miR-132, miR-184, miR-483-5p, and miR-212 (Nomura et al, 2008; Im et al, 2010; Urdinguio et al, 2010; Han et al, 2013).…”

Human induced pluripotent stem cells for modelling neurodevelopmental disorders

“…Cheung et al exploited this opportunity and derived isogenic control hiPSC lines (from RTT patient fibroblasts) expressing only the WT or the mutant MECP2 allele 92 . This pattern of X-chromosome inactivation was maintained through neuronal differentiation, and similar to Marchetto et al 74 , Djuric et al 86 , and Ananiev et al 80 (who also had an isogenic control), these studies found that RTT patient derived neurons with the mutant MECP2 allele had a reduced soma size compared to the isogenic controls patient derived neurons expressing WT MECP2.…”