一種叫做真渦蟲（Planarian）的扁形蠕蟲有著驚人的組織修復能力，把它們切成兩段后,，兩邊能再生出新的肌肉,、皮膚、腸道甚至完整的大腦,，而且這種再生好像能無限地進行下去,。美國物理學家組織網(wǎng)近日報道稱，英國諾丁漢大學研究人員揭示了它們這種無限再生壽命背后的支持機制,，為研究人類細胞克服老化,，延緩衰老特征的出現(xiàn)帶來了希望。相關(guān)論文發(fā)表在美國《國家科學院學報》上,。
細胞老化的原因之一與端粒長度有關(guān),。端粒是DNA鏈末端的“保護帽”，就像鞋帶末端防止開線的小膠棒,。細胞每分裂一次,，端粒就會變短一點，端粒變得太短時,，細胞就喪失了分裂的能力,。如果一種動物能無限地保持其端粒的長度，就可能永遠分裂下去,，它就可能永生不死,。此前的研究顯示，保持端粒長度靠的是一種端粒酶的活性,。在大部分有性繁殖生物中,，這種酶只在早期發(fā)育階段表現(xiàn)出最大活性，隨著年齡增長活性喪失,，端粒就開始變短,。
諾丁漢大學生物學院的阿齊茲·阿博貝克說，真渦蟲的干細胞卻能以某種方式避免老化過程,，保持自身細胞一直分裂下去,。在真渦蟲的成熟干細胞中,，染色體能主動保持著端粒的長度，理論上它們是永生的,。他們用兩種真渦蟲做了一系列實驗,，一種是有性繁殖，另一種是無性繁殖,，即簡單地分成兩段,。
他們識別出一段端粒酶基因，關(guān)閉了該基因活性后,，真渦蟲端粒開始變短,。然后他們檢測了該基因活性和端粒長度之間的關(guān)系，發(fā)現(xiàn)無性繁殖的真渦蟲再生時,，端粒酶基因的活性大大增加,，使干細胞能在分裂中保持端粒長度；而有性繁殖的真渦蟲卻沒顯示出這樣的情況,。研究人員對這二者間的差異非常吃驚,，因為兩種真渦蟲都有無限的再生能力。他們推測,，要么有性繁殖真渦蟲最終會出現(xiàn)端粒變短，要么它們是通過一種不需要端粒酶的機制來保持端粒長度,。
阿博貝克說,，他們的下一個目標是詳細研究這種機制，這對理解某些與老化有關(guān)的基本過程具有重要意義,。無性繁殖真渦蟲能在再生過程中保持端粒長度,，從這里有望找出讓一個動物永生不死的原因。(生物谷：Bioon.com)
doi:10.1073/pnas.1118885109
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Telomere maintenance and telomerase activity are differentially regulated in asexual and sexual worms
Thomas C. J. Tan, Ruman Rahman, Farah Jaber-Hijazi, Daniel A. Felix, Chen Chen, Edward J. Louis, and Aziz Aboobaker
In most sexually reproducing animals, replication and maintenance of telomeres occurs in the germ line and during early development in embryogenesis through the use of telomerase. Somatic cells generally do not maintain telomere sequences, and these cells become senescent in adults as telomeres shorten to a critical length. Some animals reproduce clonally and must therefore require adult somatic mechanisms for maintaining their chromosome ends. Here we study the telomere biology of planarian flatworms with apparently limitless regenerative capacity fueled by a population of highly proliferative adult stem cells. We show that somatic telomere maintenance is different in asexual and sexual animals. Asexual animals maintain telomere length somatically during reproduction by fission or when regeneration is induced by amputation, whereas sexual animals only achieve telomere elongation through sexual reproduction. We demonstrate that this difference is reflected in the expression and alternate splicing of the protein subunit of the telomerase enzyme. Asexual adult planarian stem cells appear to maintain telomere length over evolutionary timescales without passage through a germ-line stage. The adaptations we observe demonstrate indefinite somatic telomerase activity in proliferating stem cells during regeneration or reproduction by fission, and establish planarians as a pertinent model for studying telomere structure, function, and maintenance.
