你精子與她卵子是一見鍾情還是銘謝惠顧？（找了不少圖，參考參考吧）

作者：Jessica的老公│2010-01-24 11:32:21│巴幣：2│人氣：6443

雖然我的BLOG中，歷史主題偏多，但個人本業是從事醫藥研究，
偶爾還是聊聊本行的主題吧。

這篇研究很有意思，一般人體分化成熟的細胞，是很少出現細胞融合的情況，然而，精卵結合卻是例外之一，是人體中少見的『正常』細胞融合的現象（其他還有肌肉、骨頭、免疫和胎盤發育過程中會出現細胞融合），但其中的機轉到目前都未能全盤瞭解，本篇研究算是很熱門的領域。

（精卵融合）

Unlocking The Key To Human Fertility

ScienceDaily (Aug. 3, 2009) —Scientists at Leeds and Bradford have discovered a unique 『DNA signature』
in human sperm, which may act as a key that unlocks an egg’s fertility and
trigger new life.

據美國每日科學網站報道，英國科學家近日發現了人類精子獨特的『基因簽名』，對於開啟卵子的受精過程和孕育新生命起到了關鍵作用。這一發現將大大地幫助人們了解受孕的奧秘。

Drs David Miller and David Iles from the University of Leeds, in collaboration with Dr Martin Brinkworth at the University of Bradford, have found that sperm writes a DNA signature that can only be recognized by an egg from the same species. This enables fertilization and may even explain how a species develops its own unique genetic identity. Dr Iles says, 『What we have discovered is a previously unrecognized DNA packaging ‘signature’ in mammalian sperm that may be essential for successful fertilization of the egg and development of the embryo. We think it may also be ancient in origin.』

在英國生物技術及生物科學研究理事會資助下，來自利茲大學的大衛•米勒和大衛•埃爾斯博士與來自布拉德福德大學的馬丁•布林克沃思博士合作研究，發現精子會寫下一種『基因簽名』，只能被同物種的卵子所識別。精子的『基因簽名』好似鑰匙，只有被同物種的卵子識別，才能開啟受孕之鎖。精子的『基因簽名』會促進受精活動發生，也能解釋一個物種如何發育出獨特的基因特徵。埃爾斯博士說，『我們發現哺乳動物精子有‘基因簽名’，對卵子的受孕和胚胎的發育至關重要。此前人們並沒有發現精子有‘基因簽名’，我們認為‘基因簽名’存在的時間很久遠。』

（精子構造示意圖）

（由四種鹼基A、T、C、G，組成DNA序列）

Without the right ‘key’, successful fertilization either cannot occur, or if it does, development will not proceed normally. Notably, disturbances in human sperm DNA packaging are known to cause male infertility and pregnancy failures. This ‘lock and key’ mechanism has other profound implications. Not only does it explain why some otherwise healthy men produce sperm that is sterile, but it also explains how different species evolve and retain their own identity. Says Dr Miller, 『Up until now, Doctors have struggled to understand idiopathic male infertility. Our latest research offers a plausible explanation for why some sperm malfunction or fail to function correctly.』

研究人員認為，假如沒有正確的『鑰匙』來開啟生育能力的『鎖』，要麽就不能成功受精，要麽即使受精，也不會正常發育。人們已經知道人類精子DNA排列組合的紊亂會導致男性不育症和受孕失敗。而且這種『鎖鑰』機制還有更深一層的意義。它不僅能解釋為什麽有些其他方面健康的男性產生的精子卻是不育的，也能解釋不同的物種是如何進化並保持其特性的。米勒博士說：『直到現在，醫學家們還在努力探究先天性男性不育症。我們的最新研究提供了一種可能的解釋，為什麽有些精子不能正常授精或者功能障礙。』

If the DNA carried by a sperm cell was unwound and stretched out, it would actually measure more than a meter in length. In order to fit all this DNA into the microscopic space within the head of the sperm cell, the DNA needs to be very tightly coiled, or packaged. The Leeds study showed that in human and mouse sperm, not all of the DNA is packaged in the same way. Whilst most of the paternal DNA is compressed in an extremely compact fashion, some is packaged less tightly.

如果精子細胞攜帶的DNA 沒有受傷，而且伸展開的話，那麽實際上它會有一米多長。為了遷就精子細胞核的微小空間，精子DNA就必須要緊緊地卷到一起或堆疊在一起。利茲大學的研究顯示，在人類和老鼠的精子中，並不是所有的DNA都按照同樣的方式排列。大部分雄性的DNA是非常緊湊的壓縮在一起，同時有些DNA則排列得不那麽緊密。

（DNA在不同層級的折疊包裹示意）

『There is a definite pattern to the way DNA is packaged in sperm cells and we can see that this pattern is the same in unrelated fertile men. It is different in the sperm of infertile men. This implies that there is significance to the packaging of DNA that has a direct relevance to male fertility,』 says Dr Iles.

埃爾斯博士說：『精子細胞中有一種特定的DNA折疊方式。而且我們發現，即使在不相關的有生育能力的男性中，這種排列方式也是一樣的。這表明這種DNA排列方式與男性生育能力有著直接的關系。』

圖中，左邊是體細胞DNA折疊包裹方式，右邊則是精子DNA折疊包裹方式。首先，在體細胞中，DNA以每圈纏繞六個核小體，壓縮形成螺旋管狀的構造，而且每隔六萬個鹼基對與核質相接觸，此外基因表現活躍的區域也常與核質接觸。然而在精子的細胞核中，是由魚精蛋白與DNA纏繞包裹（體細胞是由組蛋白與DNA纏繞形成核小體），魚精蛋白含有高比例帶正電的精胺酸所構成，目的在於中和DNA的負電性，用以形成更緊密的螺旋構型。而此DNA螺旋構型在精子中將被迫扭成『甜甜圈狀』，而一個甜甜圈代表一個DNA環並與核質接觸。(From Ward, 1993).

Detailed analyses of the DNA in the ‘open’, less tightly packaged conformation, showed this DNA carries much of the information critical for activating genes essential for directing the development of the embryo. Further investigations showed the same conformation to exist in the sperm of several unrelated human donors and remarkably, highly similar packaging patterns to exist in the sperm of mice.

若仔細分析基因表現活躍、排列構造鬆散的DNA序列，其結果顯示，此類DNA序列攜帶著較多關鍵信息，這些信息能夠激活牽涉胚胎發育的重要基因。進一步的研究表明，相同的構造存在於無親緣關係之捐精者的精子中，更引人註目的是，相似的排列構造存在於老鼠的精子中。

DNA regions in the ‘open’ conformation may therefore be more vulnerable to damaging toxins, such as those in cigarette smoke and certain anti-cancer drugs, than those that are tightly packaged. As Dr Brinkworth says, 『this might mean that anything capable of causing genetic damage to sperm could have particular significance for the development of the embryo』.

相比於緊密排列的DNA，開放構造的DNA或許更容易受到諸如存在於香煙和有些抗癌藥物中的破壞性毒素的傷害。正如布林克沃思博士所說：『這也許意味著，那些可能對精子產生基因損害的東西，對於胚胎發育也有著重大的影響。』

The findings also help explain why inter-species breeding is so rarely successful. Where the locks and keys of two species do not match, however similar their DNA is, no viable offspring can be born. Occasionally, for example, with horses and donkeys, offspring are produced - but because the sperm and egg signatures are incompatible, their development as embryos is abnormal and any offspring are almost always infertile.

這些發現還能解釋為什麽近親物種繁殖的成功例子會這麽少。如果兩個物種的『鎖』和『鑰匙』不相配，無論它們的DNA多麽相似，都不會孕育後代。如馬和驢交配，有時候能夠產生後代。但是因為精子和卵子無法相配，其胚胎的發育是不正常的，那麽其後代幾乎都是不育的。

The research team believes that the same mechanism must also have played a role during human evolution. In the ancient history of mankind, Neanderthals co-existed with modern humans over many thousands of years. Sexual encounters between these two closely related species cannot be ruled out, yet there is no evidence in our DNA of a legacy from such couplings. It is possible that if offspring were produced, they either did not survive long or if they did, they were unable to breed.

研究小組相信相同的機制一定還在人類進化過程中發揮了重要作用。在人類早先的歷史中，穴居人與現代人類共存了幾千年。不排除曾發生過這兩個相似物種間的交配行為，但在我們的DNA中並沒有穴居人的遺傳訊息。就算當初孕育了子代，也許他們沒能存活，或是他們存活了，但也失去繁衍後代的能力。