| 摘要: | 哺乳動物的受精過程是一個包含各種生化反應的連續事件，起於精子與卵母細胞的接 觸，過程包括一系列在配子內所發生的變化，並在精卵細胞核的融合後終止。精子進入 雌性體內之後,必須進行「獲能反應」,讓精子的活動力加強並獲得受精能力，在精子接 觸卵母細胞外基質後並發生「頂體反應」後,才能使卵母細胞受精。獲能反應通常發生 於雌性的生殖器官內，如子宮或輸卵管,也可以利用人工方式在體外誘發。經過獲能反 應的精子在外觀上沒有明顯的改變，但研究顯示獲能反應後的精子內部有生化上的改 變。但是，現今我們對獲能反應在分子層級發生的確切變化以及調控的相關機制的認知 仍有不足。 生殖學家目前已證實並確認哺乳動物精子須經過獲能反應之後,才能夠進行頂體反應， 才有受精能力。精子的頂體是一種從高基氏體衍生出來的帽狀胞器，在哺乳動物中，頂 體出現在精子頭部的前半段，內含蛋白酶和醣解酶。在受精過程中，獲能反應後的精子 與卵母細胞周圍的細胞外基質接觸後，精子便開始產生改變並導致頂體表面產生小的穿 孔,精子利用胞吐作用釋放頂體內的分解酶，造成卵母細胞的胞外基質溶解，因此形成 一條可利用的通道和卵母細胞結合。 醣蛋白在精子發育的過程中密集且大量的合成, 長期以來被認為在哺乳動物的受精過 程中扮演非常重要的角色。研究結果顯示，哺乳類的精子頂體中含有許多醣化並可與凝 集素結合的分子，且在獲能反應過程中發現與醣蛋白的生成、分解和分佈有關之變化。 總之，醣化物與精子的獲能反應和頂體有著密不可分的關係,因而對受精的過程也相當 重要。然而，目前對於獲能反應相關分子和精子頂體生化組成的了解仍相當有限。 本計畫嘗試辨識小鼠精子內與獲能反應相關的醣化物分子,並鑑定頂體的生化組成。這 些資訊可以讓我們更進一步的了解這些物質在精子受精時所扮演的角色。 除此之外， 小鼠精子醣化內容物的鑑定可以協助我們確定人類精子的生化成分，因為它們可能有相 同的組成物質。最後，我們可以利用所鑑定的醣化物分子，探討頂體在精子發展中的生 物合成過程和釐清與獲能反應相關的分子機制，實驗結果可以提供日後用於臨床檢定精 子品質的準則。由於獲能反應及頂體反應對於能否成功受孕相當重要，希望藉由本計畫 的執行，使得生殖及受精相關分子的鑒定，能夠提供醫學界開發非荷爾蒙避孕藥物所需 的相關訊息。
Mammalian fertilization is a series of coordinated events involving multiple steps of mutual recognitions between haploid male and female gametes, as well as biochemical changes taking place intracellularly. Mammalian sperm capable of fertilizing oocytes are required to be “capacitated” first and this final maturation stage of sperm, termed capacitation, takes place inside the female reproductive system. Although capacitation has been shown to induce some biochemical changes; nevertheless, the exact cellular and molecular basis of capacitation underlying the reproductive functioning is still not fully understood. Only capacitated sperm recognize and bind to the extracellular matrix of an oocyte due to some unknown functional changes occur during capacitation and enable sperm undergoing acrosome reaction. The sperm acrosome is a sac-like structure surrounded by inner and outer acrosomal membranes, which contains proteases and glycohydrolases. Immediately after sperm-receptor and oocyte-extracellular matrix ligand binding, at least in the mouse, the outer acrosomal membrane fuses with the overlying plasma membrane, releasing the acrosomal contents and exposing inner acrosomal membrane (i.e. acrosome reaction). Glycoconjugates are long thought to be essential in mammalian reproduction since the sperm glycoconjugates are extensively synthesized and modified during sperm maturation and transport. Prior studies of several mammalian species revealed that sperm acrosome contain lectin binding carbohydrates, and sperm maturation such as capacitation involves the addition, removal, alternation, and/or redistribution of glycoproteins. Taken together, we know that glycosylated components that are associated with capacitation and present in acrosome are important in fertilization; however, relatively little is known about these molecules. Therefore, it is a great interest to us to identify molecules associated with capacitation and present in acrosome, and to characterize their reproductive roles and functioning in fertilization. Data obtained from this study will allow us to have a better understanding the molecular basis and changes associated with sperm capacitation during fertilization and the biochemical composition of mammalian sperm acrosome. Identification of capacitation-associated and acrosomal sperm components may give us insights into the constituents of human sperm since homologous components are likely to be present. Moreover, quantitative assessment of number of capacitated sperm which are capable of undergoing acrosome reaction is required clinically. We believe that the newly identified sperm component(s) may be used as indicative parameter(s) in assessing the maturation and quality (fertilizing ability) of sperm for patients under assisted reproduction therapy. Lastly, capacitation and acrosome are both essential for a successful fertilization taking place; therefore, we envision that the identified sperm components may be used as new targets for developing non-hormone based contraceptive drug(s). |
