皮肤细胞怎样变成神经细胞.docVIP

皮膚細胞如何變成神經細胞 How Can a Skin Cell Become a Nerve Cell 葛瑞陳?包吉爾（GRETCHEN VOGEL） 中世紀時，煉金士試圖尋找一種能將金屬冶鍊成黃金的煉金液；時至今日，生物學家猶如現代的煉金士，已經能夠利用卵母細胞（oocyte）將皮膚細胞轉變為有價值的幹細胞，甚至是完整的動物個體。經反覆實驗，科學家已經能夠輕易的進行細胞核轉殖（nuclear transfer），創造出牛、貓、老鼠、綿羊、山羊、豬，甚至如同一韓國研究團隊於五月份所宣稱的人類胚胎幹（ES）細胞。他們希望能夠更進一步將幹細胞應用於目前無法治癒的病症；然而，如同中世紀的煉金士，現在的複製技術以及幹細胞生物學家所面對的問題，也是自己尚未能完全掌握的程序：究竟是什麼作用促使卵母細胞內的細胞核發生變化呢？至今這仍是個謎。科學家仍須大量學習，才能夠像大自然般平穩地主導細胞分化，由受精卵發展成多細胞，進而製造新生兒。 ※ 圖文：細胞的煉金士（人類卵母細胞）（Cellular alchemist --- A human oocyte） Like Medieval alchemists who searched for an elixir that could turn base metals into gold, biology’s modern alchemists have learned how to use oocytes to turn normal skin cells into valuable stem cells, and even whole animals. Scientists, with practice, have now been able to make nuclear transfer nearly routine to produce cattle, cats, mice, sheep, goats, pigs, and—as a Korean team announced in May—even human embryonic stem (ES) cells. They hope to go still further and turn the stem cells into treatments for previously untreatable diseases. But like the medieval alchemists, today’s cloning and stem cell biologists are working largely with processes they don’t fully understand: What actually happens inside the oocyte to reprogram the nucleus is still a mystery, and scientists have a lot to learn before they can direct a cell’s differentiation as smoothly as nature’s program of development does every time a fertilized egg gives rise to the multiple cell types that make up a live baby. 　　科學家已經研究卵母細胞「程序重編」（reprogramming）的能力長達半個世紀之久。發展生物學家於1957 年首次發現，將成蛙細胞的細胞核置入蛙卵，可以製造出具相同基因的蝌蚪。不過50年來，卵母細胞依然是團待解之謎。 Scientists have been investigating the reprogramming powers of the oocyte for half a century. In 1957, developmental biologists first discovered that they could insert the nucleus of adult frog cells into frog eggs and create dozens of genetically identical tadpoles. But in 50 years, the oocyte has yet to give up its secrets. 這箇中的答案就在於細胞生物學。科學家了解控制發展的基因（在成人細胞內通常處於關閉狀態）會被卵母細胞再次啟動，促使細胞呈現出新受精卵般的年輕潛力。至於普通細胞如何進行閉