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.
Highlights
Rett syndrome [RTT (MIM 312750)] is a neurodevelopmental disorder that primarily affects young girls at an incidence of 1 in 10,000 live female births (Chahrour and Zoghbi, 2007)
EVALUATION OF X-chromosome inactivation (XCI) IN RTT-human induced pluripotent stem cells (hiPSCs) Given the epigenetic fluidity that exists in human pluripotent stem cell (hPSC) in the context of XCI (Hall et al, 2008; Shen et al, 2008; Silva et al, 2008; Dvash et al, 2010; Lengner et al, 2010; Tchieu et al, 2010; Pomp et al, 2011; Diaz Perez et al, 2012), it is critical to review how the XCI status was determined in RTT-hiPSCs and review the strengths and weaknesses of different technical approaches to accurately evaluate XCI (Tables 2 and 3)
The most common method of determining the XCI status in RTT-hiPSCs was the evaluation of XCI markers such as XIST by RNA-FISH and repressive chromatin marks and their mediators such as H3K27me3 and enhancer of zeste homolog2 (EZH2) by IF (Table 2)
Summary
Rett syndrome [RTT (MIM 312750)] is a neurodevelopmental disorder that primarily affects young girls at an incidence of 1 in 10,000 live female births (Chahrour and Zoghbi, 2007). Over 95% of RTT patients carry a heterozygous mutation in the X-linked gene encoding methyl-CpG binding protein 2 (MECP2; Amir et al, 1999). MECP2 functions as a transcriptional regulator by binding to the genome in a DNA methylation-dependent manner via its methyl-CpG binding domain and recruiting chromatin remodeling proteins via its transcriptional repression domain (Nan et al, 1993, 1997, 1998; Chahrour et al, 2008; Ben-Shachar et al, 2009; Skene et al, 2010). Other genes less commonly implicated in RTT include CDKL5 and FOXG1, which are located on chromosome X and 14, respectively (Scala et al, 2005; Ariani et al, 2008)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
