Transcription profiling by array of the frontal cortices of embryonic UspX knock out mice

Correct neural progenitor fate determination requires the coordination of extrinsic fate determinant signals with intrinsic responses. Post-translational modifications dynamically alter protein function and so are ideally situated to regulate development. Here we show that the deubiquitylaying enzyme, Usp9x modulates both intrinsic and extrinsic regulators of mouse neural progenitors. Nestin-cre mediated deletion of Usp9x from neural progenitors results in a transient disruption of cell adhesion and apical-basal polarity as well as the premature differentiation of intermediate neural progenitors. Ablation of Usp9x also significantly increased beta-catenin protein levels, especially S33/S37/T41 phospho-beta-catenin, and Wnt signalling. Usp9x was found to be part of the beta-catenin destruction complex and loss of Usp9x affects destruction complex composition. Notch signalling was also increased in Usp9x ablated neural progenitors, coinciding with decreased Itch and Numb, and increased Notch intracellular domain protein levels. Usp9x co-localized and immunopreciptiated with Numb from neural progenitors suggesting it is required for Numb stabilisation. These data suggest Usp9x plays a role in coordinating intrinsic responses to extrinsic signals during neural development.正确的神经前体细胞命运决定（neural progenitor fate determination）需要外在命运决定因子信号与内在应答的协同调控。翻译后修饰（post-translational modifications）可动态改变蛋白质功能，因此非常适合参与发育调控过程。本研究证实，去泛素化酶（deubiquitylating enzyme）Usp9x可调控小鼠神经前体细胞的内在与外在调节因子。通过Nestin-cre介导神经前体细胞中Usp9x的敲除，会引发细胞黏附（cell adhesion）与顶基极性（apical-basal polarity）的一过性紊乱，同时导致中间神经前体细胞（intermediate neural progenitors）过早分化。Usp9x敲除还可显著提升β-连环蛋白（beta-catenin）的蛋白水平，尤其是S33/S37/T41位点磷酸化的β-连环蛋白，并激活Wnt信号通路（Wnt signalling）。研究发现Usp9x是β-连环蛋白降解复合体（beta-catenin destruction complex）的组成部分，而Usp9x缺失会改变该降解复合体的组成。在Usp9x敲除的神经前体细胞中，Notch信号通路（Notch signalling）同样被激活，这与Itch、Numb的表达下调以及Notch胞内域蛋白水平升高相吻合。Usp9x可与神经前体细胞中的Numb发生共定位并发生免疫共沉淀（immunoprecipitation），提示Usp9x对Numb的稳定不可或缺。上述数据表明，Usp9x在神经发育过程中参与协调外在信号对应的内在应答过程。