渦蟲DDX6核糖核酸解旋酶DjCBC-1之功能研究

Abstract

再生是生物體更新或修復受損的細胞和組織，藉以維持正常生理功能與生存的方式。扁形動物渦蟲綱具有強大的再生能力，其體內存在大量多功能性成體幹細胞（neoblasts），能夠增生並分化成所有類型的細胞。因此，維持成體幹細胞增生與分化的平衡，對於渦蟲的生理恆定和再生過程都極為重要。DDX6蛋白屬於DEAD-box RNA解旋酶家族，真核生物中的DDX6同源蛋白不論在序列或功能上都具有高度保守性，並參與多項細胞生理機制。最近的研究更指出，DDX6能夠協同微核糖核酸（microRNA）影響哺乳類神經幹細胞分化，亦可透過降解mRNA和抑制轉譯的方式調控哺乳類上皮幹細胞的增生與分化。然而，對於渦蟲DDX6同源蛋白DjCBC-1是否能調控成體幹細胞增生與分化至今仍尚未明瞭。先前研究顯示，Djcbc-1表現在成體幹細胞、神經和生殖細胞當中，而抑制Djcbc-1的表現量會限制渦蟲眼點的再生。本研究進一步證實Djcbc-1高量表現於再生組織，並發現Djcbc-1的表現與否能顯著地影響處於再生期的渦蟲之存活率。除此之外，抑制Djcbc-1的表現量也會改變渦蟲腦部結構的完整性，並且大幅減弱渦蟲的負趨光性。我的研究結果顯示，Djcbc-1參與渦蟲個體的生理恆定、再生過程、以及負趨光性的調控。

Regeneration is the process of renewal and regrowth of damaged tissue to maintain the normal physiological functions for surviving. Planarian has a robust ability of regeneration. Regeneration in planarians requires neoblasts, the pluripotent somatic stem cells, which can proliferate and differentiate into all different cell types. Regulation of neoblasts proliferation and differentiation is critical for planarians homeostasis and regeneration. DDX6, a member of the DEAD-box protein family, is highly conserved among most eukaryotes. DDX6 homologs play multiple roles in many biological processes. Recent studies showed that DDX6 regulates the differentiation of mammalian neural stem cells by microRNAs, as well as regulates the proliferation and the differentiation of mammalian epidermal stem cells by mRNA degradation and translational repression. However, it is unclear that whether DjCBC-1, the DDX6 ortholog in planarians, also regulates the proliferation and differentiation of neoblasts. Previous studies showed that Djcbc-1 is expressed in neoblasts, neurons, and germline cells. In addition, depletion of Djcbc-1 limited the formation of photoreceptors. Here, I further demonstrated that Djcbc-1 is highly expressed in the regenerating tissue, and is essential for planarian survival at regeneration status. Besides, depletion of Djcbc-1 perturbed the homeostasis of brain structure and reduced the negative phototaxis in planarians. Collectively, these results suggest that Djcbc-1 participates in tissue homeostasis, regeneration, and the regulation of negative phototaxis in planarians.