[转帖]你爹是个干细胞

banned

http://sciencenow.sciencemag.org/cgi/content/full/2006/711/2

Not quite.
Mice that were the offspring of sperm derived from embryonic stem cells lived only a few days to a few months.
Credit: Karim Nayernia, Newcastle University

Your Father Was a Stem Cell
By Gretchen Vogel
ScienceNOW Daily News
11 July 2006
Scientists have managed to turn mouse embryonic stem (ES) cells into sperm that can fertilize an oocyte and produce live offspring. The feat, which is published in this month';s issue of Developmental Cell, gives researchers a potential new tool to study sperm development and could eventually help scientists understand and even treat some kinds of infertility. But the strategy is far from perfect: Only seven mice were produced from 210 fertilization attempts, and they all died at a young age.
Several teams around the world have reported that they could turn mouse ES cells into spermlike cells by adding various growth factors (ScienceNOW, 10 December 2003). But none of those sperm have proved able to fertilize an egg and produce a live pup. Karim Nayernia of the University of Göttingen in Germany and his colleagues have now managed to take that final step.
The scientists treated mouse ES cells with retinoic acid, a known factor in sperm and egg development, and then selected for cells that expressed genes typical of early sperm development. In a second step, they treated those cultures with another dose of retinoic acid. After 72 hours, they found that some of the cells started to grow tail-like structures. Additional tests suggested that many of the cells had undergone meiosis, the special cell division that produces sperm and eggs.
To test whether the lab-made sperm were truly potent, the researchers injected them into mouse oocytes and then transferred resulting embryos into surrogate mothers. In 210 attempts, the team produced 65 two-cell embryos, seven of which survived to birth. Nayernia credits their success to their two-step system, which he says is more controlled than other attempts to derive germ cells from ES cells. However, he says, the system has its flaws. All seven mice that survived to birth were either much larger or much smaller than normal pups, abnormalities typical of cloned animals. Some lived just a few days, and all died within 5 months of birth. (Normal mice live several years.)
At least some of the problems seem to be due to faults in the process of DNA imprinting, says Azim Surani of Cambridge University in the United Kingdom. Imprinting turns certain genes on or off during sperm and egg development, and defects can often lead to animals growing larger or smaller than normal. The work "is an important piece of research," Surani says, but he adds, it';s clear that sperm development has yet to give up its key secrets.