Isotani Ayako, Nakanishi Tomoko, Kobayashi Shin, Lee Jiyoung, Chuma Shinichiro, Nakatsuji Norio, Ishino Fumitoshi, Okabe Masaru
Genome Information Research Center and Graduate School of Pharmaceutical Sciences, Osaka University, 3-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
Proc Natl Acad Sci U S A. 2005 Mar 15;102(11):4039-44. doi: 10.1073/pnas.0406769102. Epub 2005 Mar 3.
We produced XX<-->XY chimeras by using embryos whose X chromosomes were tagged with EGFP (X*), making the fluorescent green female (XX*) germ cells easily distinguishable from their nonfluorescent male (XY) counterparts. Taking advantage of tagging with EGFP, the XX* "prospermatogonia" were isolated from the testes, and the status of their genomic imprinting was examined. It was shown that these XX cells underwent a paternal imprinting, despite their chromosomal constitution. As previously indicated in sex-reversal XXsxr testes, we also found a few green XX* germ cells developed as "eggs" within the seminiferous tubules of XX*<-->XY chimeric testes. These cells were indistinguishable from XX* prospermatogonia at birth but resumed oogenesis in a testicular environment. The biological nature of the "testicular eggs" was examined by recovering the eggs from chimeric testes. The testicular eggs not only formed an egg-specific structure, the zona pellucida, but also were able to fuse with sperm. The collected testicular eggs were indicated to undergo maternal imprinting, despite the testicular environment. The genomic imprinting did not always follow the environmental conditions of where the germ cells resided; rather, it was defined by the sex that was chosen by the germ cells at early embryonic stage.
我们通过使用X染色体标记有增强绿色荧光蛋白（X*）的胚胎来制备XX<-->XY嵌合体，使得发出绿色荧光的雌性（XX*）生殖细胞易于与其不发荧光的雄性（XY）对应细胞区分开来。利用增强绿色荧光蛋白标记，从睾丸中分离出XX*“精原细胞”，并检测其基因组印记状态。结果表明，尽管这些XX细胞具有其染色体组成，但它们经历了父本印记。正如之前在性反转XXsxr睾丸中所表明的那样，我们还发现在XX*<-->XY嵌合睾丸的生精小管内，一些绿色的XX生殖细胞发育成了“卵子”。这些细胞在出生时与XX精原细胞无法区分，但在睾丸环境中恢复了卵子发生。通过从嵌合睾丸中回收卵子来检测“睾丸卵子”的生物学特性。睾丸卵子不仅形成了卵子特异性结构——透明带，而且还能够与精子融合。尽管处于睾丸环境中，但收集到的睾丸卵子被表明经历了母本印记。基因组印记并不总是遵循生殖细胞所处的环境条件；相反，它是由生殖细胞在胚胎早期选择的性别所决定的。
