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 [学科进展]：讨论医学遗传学的研究进展、新技术、新方法、新理论在治疗、预防遗传病的应用等。 |
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| 作者：[游客] |
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 2005-12-3 10:12:08 |
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 雌性动物排出卵子，雄性动物制造精子，这简直是无可置疑的事实。但日本研究人员发现，事情并非总如此简单：他们成功地使雄性小鼠睾丸中长出了卵子。
小鼠胚胎发育过程中，在雌性和雄性胚胎中，那些将要形成睾丸或卵巢的细胞（即生殖细胞）起初都是一样的。在雄性体内，Y染色体上一个称为Sry的基因在妊娠中期开启，促使生殖细胞发育成睾丸和精子。雌性没有Sry基因，生殖细胞就发育成卵巢和卵子。
但如果将雌性生殖细胞放在雄性细胞中间，会发生什么事？这个细胞是会受到雄性细胞信号影响而发展成精子呢，还是沿着自己本来的方向变成卵子？大阪大学的冈部胜及其同事认为应该是前一种情况。
为了验证这一观点，他们分别从雄性和雌性小鼠胚胎中提取细胞，混合到一起，植入小鼠体内使其生长。
实验显示，在雄鼠睾丸内生长的雌鼠细胞大多放弃了其本来的遗传特征，进入精子发育的早期阶段，这与此前一些研究结果一致。冈部发现，周围有着活跃Sry基因的雄鼠细胞，会发出信号，使雌性生殖细胞产生一些基因活动，这些活动通常只有雄性细胞才具备。
但科学家还发现，尽管如此，植入睾丸的雌性生殖细胞有少数还是发育成了卵子。这些卵子可以与精子结合，但未能进一步发育成胚胎。有关论文发表在《国家科学院学报》(PNAS)上。冈部胜将这些特殊的卵子称为“睾丸卵子”，说这个结果非常令人惊讶。
细胞口袋
有关睾丸卵子的研究并不是第一次。早在25年前就有人报告说，在雄鼠体内发现了似乎是卵子的细胞。但当时仅根据细胞的形状和大小来判断它们是卵子，不完全可靠。冈部等人首次使用了遗传学技术，证实这些细胞属于雌性。
英国剑桥Babraham研究所的卵子和精子发育专家Wolf Reik说，这些卵子之所以能够形成，可能是睾丸中有着由雌性细胞构成的小“口袋”，在口袋中发育的细胞可不受雄性细胞影响，继续发育成卵子。
科学家希望这一发现可帮助研究染色体紊乱导致的性器官发育异常等疾病。例如Klinefelter综合征（先天性睾丸发育不全症，原发性小睾丸症）患者体内携带一个多余的X染色体，其生殖细胞在发育过程中消失，基本不能产生精子。
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| 作者：[游客] |
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2005-12-9 16:41:23 |
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 怎么图不显示?
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| 作者：[游客] |
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2005-12-9 22:13:13 |
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有图呀!
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