Wu H, Fässler R, Schnieke A, Barker D, Lee K H, Chapman V, Francke U, Jaenisch R
Whitehead Institute for Biomedical Research, Nine Cambridge Center, MA 02142.
Development. 1992 Nov;116(3):687-95. doi: 10.1242/dev.116.3.687.
Transgenic mice carrying one complete copy of the human alpha 1(I) collagen gene on the X chromosome (HucII mice) were used to study the effect of X inactivation on transgene expression. By chromosomal in situ hybridization, the transgene was mapped to the D/E region close to the Xce locus, which is the controlling element. Quantitative RNA analyses indicated that transgene expression in homozygous and heterozygous females was about 125% and 62%, respectively, of the level found in hemizygous males. Also, females with Searle's translocation carrying the transgene on the inactive X chromosome (Xi) expressed about 18% transgene RNA when compared to hemizygous males. These results were consistent with the transgene being subject to but partially escaping from X inactivation. Two lines of evidence indicated that the transgene escaped X inactivation or was reactivated in a small subset of cells rather than being expressed at a lower level from the Xi in all cells, (i) None of nine single cell clones carrying the transgene on the Xi transcribed transgene RNA. In these clones the transgene was highly methylated in contrast to clones carrying the transgene on the Xa. (ii) In situ hybridization to RNA of cultured cells revealed that about 3% of uncloned cells with the transgene on the Xi expressed transgene RNA at a level comparable to that on the Xa. Our results indicate that the autosomal human collagen gene integrated on the mouse X chromosome is susceptible to X inactivation. Inactivation is, however, not complete as a subset of cells carrying the transgene on Xi expresses the transgene at a level comparable to that when carried on Xa.
携带人类α1（I）胶原蛋白基因完整拷贝位于X染色体上的转基因小鼠（HucII小鼠）被用于研究X染色体失活对转基因表达的影响。通过染色体原位杂交，转基因被定位到靠近Xce位点的D/E区域，Xce位点是控制元件。定量RNA分析表明，纯合和杂合雌性小鼠中转基因的表达分别约为半合子雄性小鼠中表达水平的125%和62%。此外，携带转基因的Searle易位雌性小鼠在失活的X染色体（Xi）上表达的转基因RNA约为半合子雄性小鼠的18%。这些结果与转基因受到X染色体失活但部分逃脱一致。两条证据表明，转基因逃脱了X染色体失活或在一小部分细胞中被重新激活，而不是在所有细胞中从Xi上以较低水平表达，（i）在Xi上携带转基因的9个单细胞克隆中，没有一个转录转基因RNA。在这些克隆中，转基因高度甲基化，这与在Xa上携带转基因的克隆形成对比。（ii）对培养细胞RNA的原位杂交显示，约3%在Xi上携带转基因的未克隆细胞表达的转基因RNA水平与在Xa上时相当。我们的结果表明，整合在小鼠X染色体上的常染色体人类胶原蛋白基因易受X染色体失活影响。然而，失活并不完全，因为在Xi上携带转基因的一部分细胞表达转基因的水平与在Xa上携带时相当。
