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Updated: Jun 13, 2026

Pooled shRNA Screen for Reactivation of MeCP2 on the Inactive X Chromosome
Published on: March 2, 2018
Two-step imprinted X inactivation: repeat versus genic silencing in the mouse
Satoshi H Namekawa1, Bernhard Payer, Khanh D Huynh
1Howard Hughes Medical Institute, Department of Molecular Biology, Massachusetts General Hospital, Department of Genetics, Harvard Medical School, Boston, MA, USA.
Mammals use X chromosome inactivation (XCI) to balance gene dosage. Paternal X chromosome (X(P)) inactivation in early embryos occurs in two steps: repeat silencing then gene silencing, with Xist RNA acting late.
Area of Science:
- Genetics
- Epigenetics
- Developmental Biology
Background:
- Mammals equalize X-linked gene expression through X chromosome inactivation (XCI) in females.
- Imprinted XCI, selectively silencing the paternal X chromosome (X(P)), occurs in marsupials and early mouse embryos.
- The precise mechanisms governing imprinted X(P) silencing remain largely unknown.
Purpose of the Study:
- To elucidate the mechanisms and temporal events underlying imprinted paternal X chromosome inactivation (X(P)) in early mouse development.
- To investigate the roles of repetitive elements and Xist RNA in the two-step process of X(P) silencing.
Main Methods:
- Analysis of gene silencing dynamics during preimplantation mouse development.
- Investigation of the role of Xist RNA in different stages of X chromosome inactivation.
- Examination of gene translocation relative to silenced regions on the X chromosome.
Main Results:
- The imprinted X(P) is functionally divided into genic and intergenic repetitive element domains.
- Repetitive element silencing on X(P) precedes genic silencing, occurring by the two-cell stage independently of Xist.
- Genic silencing initiates later (morula-to-blastocyst stage), requires Xist, and involves gene translocation into presilenced repeat regions.
Conclusions:
- Imprinted XCI occurs in a two-step manner: repeat silencing followed by Xist-dependent genic silencing.
- Nucleolar association may contribute to the epigenetic asymmetry between paternal (X(P)) and maternal (X(M)) X chromosomes.
- A model is proposed where transgenerational epigenetic information is carried by repeats or involves parent-of-origin-specific silencing of repetitive elements.
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15:54Combined DNA-RNA Fluorescent In situ Hybridization (FISH) to Study X Chromosome Inactivation in Differentiated Female Mouse Embryonic Stem Cells
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