探討USP11在神經細胞分化決定上扮演的角色

Abstract

在降解體路徑中，泛素藉由E3泛素連結酶的作用連接到目標蛋白質上，亦可被去泛素酶將泛素移除，雖然許多E3泛素連結酶已知在神經發育中扮演重要的角色，但對於去泛素酶了解甚少。在先前對於去泛素酶中USP家族的一員：USP11的研究中，我們實驗室發現抑制USP11有助於Notch對增加神經膠瘤初始細胞展現幹細胞特性的影響，有鑑於Notch訊息在控制神經幹細胞(stem cells)或神經前驅細胞的自我更新以及分化有重要的影響，我們進一步研究USP11在神經生成中的表現和功能。藉由原位雜合技術，我們發現USP11主要表現在發育中的中樞神經系統，其中包含小鼠胚胎期E12.5, E14.5和E17.5新皮層區的皮層板內。利用小鼠胚胎幹細胞進行體外誘導神經分化的技術，我們發現USP11隨著幹細胞分化成神經細胞表現量明顯上升，此外也發現在幹細胞中過度表現USP11會造成神經前驅細胞提早分化成神經細胞。相反地，當剔除USP11使得神經前驅細胞分化成神經細胞的能力受損。另一個有趣的發現，表現過多無催化活性的USP11突變體並不會促進神經前驅細胞分化成神經細胞，反而導致分化成神經膠細胞。透過從子宮基因剔除技術得到的活體結果，更加證實了體外實驗的結果。總之，我們的研究確認USP11對於神經命運的決定上扮演關鍵角色，後續我們的目標為找出USP11調控此功能的受質。

In the ubiquitin-proteasome pathway, ubiquitin is conjugated to the target proteins by ubiquitin E3 ligases and removed by deubiquitinating enzymes (DUBs). Although a number of E3 ligases are known to play roles in neural development, little is known about the function of DUBs in this process. Previous studies in our laboratory revealed that the repression of USP11, a USP family of DUB, contributes to the effect of Notch on potentiating the stemness properties of glioma-initiating cells. Given the importance of Notch signaling in controlling neural stem/progenitor cells self-renewal and differentiation, we investigated the expression and function of USP11 during neurogenesis. By in situ hybridization, we found that USP11 is most abundantly expressed in developing central nervous system, including cells located in cortical plate of neocortex in E12.5, E14.5 and E17.5 of mouse embryos. Using an ex vivo neural differentiation protocol of mouse embryonic stem (ES) cells, we found that USP11 expression is up-regulated during ES cells differentiation into neural progenitor cells (NPC) and further up-regulated during NPC differentiation into neurons. Consistent with this finding, overexpression of USP11 in ES cells leads to a precocious NPC and neuron differentiation, as evident by earlier induction of NPC and neuron markers. In contrast, depletion of USP11 attenuates NPC differentiation and impairs neuron differentiation. Interestingly, overexpression of a catalytically inactive mutant of USP11 does not promote NPC and neuron differentiation, but leads to an induction of glial cell fate. These ex vivo data were further verified by in vivo studies with an in uterus gene delivery technique. Together, our data identify a critical role of USP11 in neural fate determination. Future study will aim to identify USP11 substrate that mediates this function.