anybody who has, for whatever reason, dreamed of a world without men in the past probably looked to the cloners to make it happen. few would have imagined it might one day be possible to create human sperm in a laboratory, but that is now the proud claim of professor karim nayernia of the north east england stem cell institute.
it is a claim that immediately hit controversy. allan pacey of the university of sheffield, a sperm biologist of 20 years standing, declared he was unconvinced. azim surani, a professor of physiology and reproduction at cambridge university, said they were "sperm-like cells" and "a long way from being authentic sperm cells".
reactions two years ago, when the same team not only grew mouse sperm from embryonic cells but used it to produce baby mice, were somewhat warmer, which perhaps says something about the sensitivities around the creation of human sperm. pacey said at the time that the mouse experiment would be "very useful to study the basic biology of sperm production".
using technology to produce the essence of human life is a sensitive matter: the baby mice all died after a few months. and while the newcastle scientists have categorically ruled out the use of their manufactured sperm for reproduction and say they understand people's concerns, the very notion that human sperm have been created from stem cells has taken anxieties to a new level.
"the law specifically does not allow artificially created sperm to be used to fertilise an egg for the sake of reproduction," says professor peter braude, head of the department of women's health in the division of reproduction and endocrinology at king's college london. and even if the law is changed, he asks, "what experiments are you going to do to make it safe?" citing dolly the sheep, braude points out that cloning has been shown to be unsafe, and there's no reason to suppose lab-created sperm will be any safer.
still, all the experts say what has been done in newcastle is interesting and good for research. discovering how to make sperm will teach us more about sperm malfunction, and therefore could help treat infertile men, rather than replace them.
the newcastle team used stem cells from a leftover embryo donated after fertility treatment, and used chemicals to encourage their growth. they could not use just any kind of stem cells, however. they selected only those with the potential to become sperm - the so-called "germline" cells, which were a small proportion of the total.
over four to six weeks, these cells developed and were prompted to undergo the process of "meiosis", which halved the number of chromosomes they carried - a hallmark of sperm. the woman's egg must contribute the rest of the chromosomes needed by an embryo.
interestingly, the team's success came from stem cells with xy (male) chromosomes. the same process on xx (female) stem cells did not work, which seems to suggest that the male of the human species is not yet wholly superfluous.
任何在过去曾梦想世界上没有男同胞的女同胞们，不论出于什么原因，都很可能寄希望于克隆来成就这一梦想。很少有人会想到，终有一天实验室可以制造精子，然而，英格兰东北部干细胞研究所（north east england stem cell institute，注，隶属纽卡斯尔大学 university of newcastle 。）教授卡里姆•纳耶尼亚（karim nayernia）却能自豪地宣称自己业已修成这一“功德”。
这一宣称一发布，就遭惹了争议。迎着20年资历的谢菲尔德大学精子生物学家艾伦·帕西（allan pacey）宣布他对此不相信。剑桥大学生理及生殖教授阿奇姆·苏拉尼（azim surani）认为那些不过是“类似精子的细胞”，并且“离真正的精子细胞还有‘很长的路要走’。”
同样还是这个研究小组，在两年前不单单从老鼠的胚胎干细胞中制造出老鼠精子，而且还成功地利用这老鼠精子培育出小老鼠，那时接受到的反应多少比这次积极点。这或许道出了制造人类精子这一课题的敏感性。帕西当时表示，对老鼠的这一实验会“有助于研究精子制造的基本生物学机制。”
利用生物技术制造人类生命的“种子”，这是一个非常敏感的问题：那些小老鼠在几个月之后全部死亡了。纽卡斯尔大学所属的英格兰东北部干细胞研究所的科学家们明确否认了利用其人造精子进行婴儿培育的意图，并表示他们完全理解大众对此的关注，然而，人类已成功地从干细胞中制造出人类精子的这一观念，不由得加重了大众的担忧。
“法律明确规定，不允许将人造精子用于卵子受精以达到培育婴儿的目的，”伦敦大学国王学院（king's college london）生殖及内分泌部女性健康系主任彼得•布劳德（peter braude）教授说。即使法律改变，他问到：“你打算做哪些实验以确保这种方式的安全性呢？”布劳德援引了人工克隆的多莉羊，他指出，克隆技术已被证明缺乏安全性，因此，没有理由可以假设实验室的人造精子会比较安全。
尽管如此，所有的专家们都表示，纽卡斯尔大学完成的这项研究是很令人感兴趣的，有利于行业今后的研究。对于如何制造精子的探索能为我们揭示更多有关精子失能的秘密，因此有助于治疗不育男性，而不是取代他们。
纽卡斯尔大学的这一研究小组利用不育治疗多余下来的捐赠胚来提取干细胞，并利用化学药剂帮助干细胞的生长。然而，不是任何种类的干细胞对他们都有用，他们只选择那些有潜力成为精子的干细胞来培育——这些干细胞被称为“生殖”细胞，只占很小的比例。
四到六周之后，这些干细胞培育成熟，刺激它们进入“成熟”过程，所附的作为精子标志的染色体数量将在此过程中减半。女性卵子须提供人体胚胎所需余下部分的染色体。
有趣的是，这个研究小组只培育成功自带xy（男性）染色体的干细胞。同样的步骤尚无法培育出自带xx（女性）染色体的干细胞，这似乎表明，男性尚未完全是多余的。