Escape from Imprinted Inactivation in 8.5 dpc Carrier Female Embryo
A cross was carried out between a carrier female (Atrx WT/null) and wild-type male (Atrx WT/Y), and embryos were dissected in their deciduas at 8.5 dpc. Any carrier female progeny of this cross will carry an Atrx WT allele on the Xp chromosome and an Atrx null allele on the Xm chromosome. Transverse paraffin sections were stained with the anti-ATRX antibody (H-300).
(A) High-magnification image (400×) of the neural fold region (nf) (embryo proper) of a carrier female (Atrx WT/null) embryo. This tissue is clearly comprised of a mosaic of Atrx-positive and Atrx-negative cells due to random X-inactivation. This section was counterstained with haematoxylin.
(B) High-magnification image (400×) of the same embryo depicted in (A), showing the extraembryonic derived-chorionic ectoderm (ce) and visceral endoderm (ve), two tissues that undergo imprinted X-inactivation. Although Atrx is poorly expressed in the visceral endoderm (even in wild-type females [unpublished data]), strong expression of Atrx can be seen in the chorionic ectoderm, indicating that the paternally-derived Atrx WT allele had escaped inactivation in this tissue.
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