Figure 1. X chromosome inactivation during female mouse development.

Figure 1

X chromosome inactivation during female mouse development. During early mouse development, at the 2 to 8 cell stage, imprinted XCI is initiated, in which the paternal X chromosome is always inactivated (Xpi, red cells). Imprinted XCI is maintained in the extraembryonic trophectoderm (the future placenta) and the primitive endoderm. In the inner cell mass of the blastocyst, imprinted XCI is reversed and both X chromosomes again become transcriptionally active (XaXa, grey). Around the time of implantation of the embryo in the uterus, random XCI starts in the fetal precursor cells which arise from the ICM of the early embryo (XiXa, blue cells paternal X active, red cells maternal X active). XCI is thus coupled to development and cell differentiation. Therefore embryonic stem (ES) cells, which are isolated from the ICM of the blastocyst, can be used to study XCI in vitro, as random XCI is initiated in female ES cells upon differentiation. A color version of this figure is available at www.landesbioscience.com/curie.

From: X Chromosome Inactivation and Embryonic Stem Cells

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