| 摘要: | 哺乳類動物的受精過程是單套的精子及卵子之間相互辨識的一連串過程。雖然精子的發育 是在雄性生殖腺中，但是在射精後，精子必需在雌性的生殖通道中經過最後的步驟，才能 達到成熟階段並具有受精的能力。這個必要階段，稱為精子的獲能反應。在獲能反應中， 哺乳類動物的精子在生化及分子層級進行改變，同時進行轉錄體的修飾。然而，獲能反應 的分子機制對於生殖功能到底有何貢獻，目前仍不完全清楚。 大部分的男性生殖學家認為，精子的功能是載具，其唯一的任務是把父系的基因體運送到 卵子。近年來，越來越多的研究表明，精子核中確實有 RNA 存在，且多樣性相當高，包含 微型 RNA (miRNA)在內。然而卻鮮少有研究深入瞭解這些轉錄體的種類及組成，故對於獲 能反應後的精子轉錄體及其功能缺乏深入的瞭解。精子中 DKK, IGF-2R,和 c-kit 等 miRNA 的相關研究，讓學者瞭解到精子不僅僅只是載具，精子內的「表觀遺傳調控因子」及「轉 錄體」對於胚胎早期的發育也具有重要的貢獻。因此，對於獲能反應後精子所含表觀遺傳 因子的鑒定，並釐清精子在生殖方面的貢獻，有助於解決這方面的疑問。 如前所述，精子成熟之後確實攜帶了表觀遺傳因子所構成的轉錄體，而最近的研究則發 現，經過獲能反應後的精子有轉譯及轉錄活動的證據，使得精子與胚胎早期發育有關的觀 點可信度更高。 綜合這些研究所推導出的假說，認為獲能反應的過程不僅使精子具有受 精的能力，同時精子可能重整 miRNA 的轉錄體，使其具有調控受精後胚胎早期發育的能力。 因此，完整的研究精子經獲能反應後父系 miRNA 轉錄體，有助於驗證這個假說。 本研究將解析 miRNA 在精子獲能反應階段後的表達，並偵測胚胎早期發育過程中,miRNA 表 觀遺傳因子所扮演的角色。藉由分析精子獲能反應後的轉錄體，期望對於建立正常生殖功 能男性的基因指紋圖譜或提升男性精子的受精能力等方面有正面的助益。同時可以增加男 性不孕症的病理診斷能力，增強人工生殖技術。小鼠精子可能具有人類 miRNAs 的同源分 子，故小鼠精子 miRNA 的研究可以提供對於人類精子轉錄體的瞭解。本研究探討獲能反應 相關 miRNA 對早期胚胎的調控機制，期能藉此發展無荷爾蒙避孕的新措施。
Mammalian fertilization is a series of coordinated events involving multiple steps of mutual recognitions between haploid male and female gametes. The development of male gamete starts in the gonads and freshly ejaculated sperm are required to undergo a final obligatory maturation step, termed capacitation, in the female reproductive track in order to become FULLY fertilizable. During capacitation, mammalian sperm undergo biochemical and molecular changes, as well as modification of transcriptome. Nevertheless, the exact molecular basis of capacitation underlying the reproductive functioning is still not fully understood. The majority of andrologists endorse the view that sperm is just a vehicle for transporting the paternal genome to the oocyte and nothing more. Recently, an increasing number of studies report the presence of diverse RNA populations, including microRNA (miRNA), in the sperm nucleus; nevertheless, little is known about the exact transcriptomic composition in fertile capacitated sperm. Interestingly, studies of "epigenetic regulators" and "sperm transcriptome", such as miRNAs of DKK, IGF-2R, and c-kit in sperm, has led scientists to realize that sperm also play roles in early embryogenesis. To tackle some of the misconceptions surrounding the paternal contribution in reproduction and embryonic development, identification of epigenetic factors delivered by "capacitated sperm" upon fertilization are in need. Based on the proceeding review, we know that fertile sperm carries epigenetic factors constituting the paternal transcriptome. Recent finding for the demonstration of transcriptional and translational activity in capacitated sperm, as well as examples of sperm-borne miRNAs dictate early embryogenesis reinforces this idea. All together, an intriguing hypothesis put forward in all these studies is that the process capacitation not only enables sperm to be fully fertilizable but also allows paternal microRNA transcriptome to be reassembled in order to regulate early embryogenesis following fertilization. Therefore, a complete transcriptomic survey of paternal miRNAs in capacitated sperm is required to test this hypothesis. In this proposed study, we will conduct a stage-specific miRNA expression profiling of sperm capacitation and to characterize the reproductive role(s) of capacitation-associated miRNAs in paternal epigenetic regulation during early embryogenesis. We believe that transcriptomic profiling data of sperm capacitation obtained from this study could be used as a genetic fingerprint of normal fertile men, as well as prognostic assessment of male fertility. The information will also have clinical implications in etiological diagnosis of male infertility and in the practice of assisted reproductive technologies. Moreover, murine sperm miRNAs may give us insights into the transcriptome of human sperm since homologous molecules are likely to be present. Finally, it is tempting to envision the possibility that the capacitation-associated microRNAs that are involved in early embryogenesis may be used as new targets for developing non-hormone based contraceptive control. |
