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2_test

{"project":"2_test","denotations":[{"id":"16628246-1152998-85799757","span":{"begin":1011,"end":1013},"obj":"1152998"},{"id":"16628246-6185603-85799758","span":{"begin":1140,"end":1142},"obj":"6185603"},{"id":"T777","span":{"begin":1011,"end":1013},"obj":"1152998"},{"id":"T63330","span":{"begin":1140,"end":1142},"obj":"6185603"}],"text":"Escape from Imprinted Inactivation of the Paternally Inherited Atrx WT Allele in Extraembryonic Tissues of Carrier Female Mice\nFemale mice carrying an Atrx null allele (Atrx WT/null;GATA1-cre +/−) were detected at 9.5 dpc (Table 1) and recovered at birth (unpublished data), although at both time points the number of carrier females was lower than that of wild-type (Atrx WT/WT;GATA1-cre +/−) females, suggesting that a proportion of carrier female embryos died in utero. Surviving adult carrier female mice were not phenotypically normal and exhibited mild behavioural abnormalities, although some could reproduce. For all Atrx WT/null carrier female embryos presented in Table 1, the Atrx WT allele was paternally derived, while the Atrx null allele was maternally derived. In the mouse, X chromosome inactivation is subject to parental imprinting in the trophectoderm and primitive endoderm lineages that give rise to the extraembryonic tissues, resulting in inactivation of the paternal X chromosome (Xp) [18]. In contrast, in tissues of the embryo proper (derived from the inner cell mass of the blastocyst) X-inactivation is random [19]. Thus, in the extraembryonic compartment of Atrx WT/null carrier females, normal imprinted X-inactivation would be expected to result in silencing of the paternally derived Atrx WT allele, leaving only the Atrx null allele on the active maternal X (Xm) and thereby render the extraembryonic tissues null for full-length Atrx protein. However, the absence of Atrx in the extraembryonic compartment is lethal in Atrx null/Y males. This suggested the possibility of an escape from imprinted inactivation of the paternally derived Atrx WT allele in the extraembryonic compartment of a proportion of carrier female embryos.\nTo investigate further, we crossed homozygous Atrx flox/flox females and homozygous GATA1-cre transgenic males (Atrx WT/Y;GATA1-cre +/+), which would be expected to yield only Atrxnull males (Atrxnull/Y;GATA1-cre +/−) and carrier females (Atrx WT/null;GATA1-cre +/−). In these carrier females, the Atrx WT allele is paternally inherited. Embryos were dissected in their deciduas at 7.5 dpc, and paraffin sections were stained with anti-ATRX antibody, along with sections from a wild-type 7.5 dpc embryo for comparison (Figure 8). As described above, Atrx expression was detected in every cell in the epiblast (embryo proper) region of wild-type 7.5 dpc embryos (Figure 8B). In contrast, the epiblast region of carrier female embryos was composed of a mosaic of small clusters of Atrx-positive cells (in which the Atrx null allele on Xm had been inactivated) and Atrx-negative cells (in which the Atrx WT allele on Xp had been inactivated), indicating that the Atrx gene was subject to normal random X-inactivation in the epiblast. Remarkably, clear Atrx expression could also be detected in the extraembryonic tissues of carrier females, as shown in the extraembryonic-derived chorionic ectoderm (Figure 8C). Atrx expression could be detected in almost all cells of the chorionic ectoderm. Atrx expression was also clearly detected in other extraembryonic structures, including TGCs (unpublished data). Escape from silencing of an Xp-inherited Atrx WT allele was also observed in the chorionic ectoderm of carrier females at 8.5 dpc (Figure S4). Thus, although random X-inactivation occurs normally within the epiblast, the Atrx WT allele (inherited on the Xp chromosome) escaped the normal imprinted X-inactivation in the extraembryonic compartment of some carrier females.\nFigure 8 Escape from Imprinted Inactivation of the Paternally Inherited AtrxWT Allele in Carrier Females\nParaffin sections of wild-type (Atrx WT/Y) and carrier female (Atrx WT/null) 7.5 dpc embryos (dissected in their deciduas) were stained with the anti-ATRX antibody (H-300). Scale bars represent 200 μm (40× magnification) or 20 μm (400× magnification).\n(A) Stained sections showing whole embryos at 40× magnification. a, amnion; c, chorion; e, epiblast; ep, ectoplacental cone.\n(B) Higher-magnification image (400×) of the epiblast regions of the stained sections shown in (A).\n(C) Higher-magnification image (400×) showing the extraembryonic derived-chorionic ectoderm of the stained sections shown in (A). ce, chorionic ectoderm; cm, chorionic mesoderm."}

craft-ca-core-dev

PMC:1440874 / 31670-35968 JSONTXT

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craft-sa-dev

craft-ca-core-ex-dev

2_test

craft-ca-core-dev

PMC:1440874 / 31670-35968 JSON TXT