Nuclear Prospero allows one-division potential to neural precursors and post-mitotic status to neurons via opposite regulation of Cyclin E.
Nuclear Prospero allows one-division potential to neural precursors and post-mitotic status to neurons via opposite regulation of Cyclin E.
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DOI：
10.1371/journal.pgen.1010339
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发表时间：
2022-08
期刊：
影响因子：
4.5
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中科院分区：
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在果蝇胚胎中枢神经系统中，称为神经母细胞（NB）的多能干细胞通过自我更新的不对称分裂进行分裂，并产生称为神经节母细胞（GMC）的双能前体细胞。 GMC 仅分裂一次，产生两个不同的有丝分裂后神经元。赋予前体细胞单次分裂潜能的基因和途径或神经元如何进入有丝分裂后尚不清楚。有人提出，当同源结构域蛋白 Prospero (Pros) 定位于细胞核时，会限制前体细胞的干细胞潜力。在这里，我们展示了核 Prospero 被磷酸化，并与染色质结合。在 MP2 等 NB 谱系或 GMC4-2a 等 GMC 谱系中，Pros 允许子代神经元具有一分裂潜力以及有丝分裂后状态。这些事件是通过增强前体中细胞周期蛋白 E 的表达并抑制有丝分裂后神经元中的表达来介导的。因此，在缺乏 Pros 的情况下，Cyclin E 在 MP2 细胞中下调。因此，MP2 无法分裂，而是分化为两个子代神经元之一。在子代细胞中，Pros 逆转其作用并增强 Cyclin E 的下调，使神经元退出细胞周期。因此，在较老的 pro 突变体胚胎中，Cyclin E 在后代细胞中上调。这些结果阐明了前体细胞的分裂潜能和子代细胞有丝分裂后状态的长期存在的问题，以及反向微调细胞周期蛋白 E 表达如何控制这些基本的细胞事件。这项工作还揭示了 Pros 的翻译后修饰决定了其细胞质与核定位。在这项研究中，首先，我们深入了解磷酸化在 Prospero 的细胞质与核定位中的作用。在自我更新的多能前体干细胞中，它是非磷酸化的，位于细胞质中，而在中枢神经系统的双能前体细胞中，它是磷酸化的，位于细胞核中。其次，我们证明核易位和 Pros 与染色质的结合指定了双能前体细胞的单分裂潜力。我们的实验进一步表明，这是通过增强 Cyclin E 表达的上调来实现的。然而，分裂后，在子代细胞中，Pros 增强了 Cyclin E 表达的下调，使子代细胞退出细胞周期并进入有丝分裂后。这些结果揭示了前体细胞单次分裂潜力和子代细胞有丝分裂后状态的长期存在的问题。 Prospero 通过在不同发育时间点以相反方向调节 Cyclin E 似乎实现了神经发生过程中的这些关键里程碑。
In Drosophila embryonic CNS, the multipotential stem cells called neuroblasts (NBs) divide by self-renewing asymmetric division and generate bipotential precursors called ganglion mother cells (GMCs). GMCs divide only once to generate two distinct post-mitotic neurons. The genes and the pathways that confer a single division potential to precursor cells or how neurons become post-mitotic are unknown. It has been suggested that the homeodomain protein Prospero (Pros) when localized to the nucleus, limits the stem-cell potential of precursors. Here we show that nuclear Prospero is phosphorylated, where it binds to chromatin. In NB lineages such as MP2, or GMC lineages such as GMC4-2a, Pros allows the one-division potential, as well as the post-mitotic status of progeny neurons. These events are mediated by augmenting the expression of Cyclin E in the precursor and repressing the expression in post-mitotic neurons. Thus, in the absence of Pros, Cyclin E is downregulated in the MP2 cell. Consequently, MP2 fails to divide, instead, it differentiates into one of the two progeny neurons. In progeny cells, Pros reverses its role and augments the downregulation of Cyclin E, allowing neurons to exit the cell cycle. Thus, in older pros mutant embryos Cyclin E is upregulated in progeny cells. These results elucidate a long-standing problem of division potential of precursors and post-mitotic status of progeny cells and how fine-tuning cyclin E expression in the opposite direction controls these fundamental cellular events. This work also sheds light on the post-translational modification of Pros that determines its cytoplasmic versus nuclear localization. In this study, first, we provide insight into the role of phosphorylation in the cytoplasmic versus nuclear localization of Prospero. It is non-phosphorylated and cytoplasmic in self-renewing multipotential precursor stem cells, whereas phosphorylated and nuclear in bipotential precursor cells in the CNS. Second, we show that nuclear translocation and binding of Pros to chromatin specifies the single-division potential of bipotential precursor cells. Our experiments further show that this is achieved by augmenting the upregulation of Cyclin E expression. However, following the division, in the progeny cells, Pros augments the downregulation of Cyclin E expression, allowing the progeny cells to exit the cell cycle and become post-mitotic. These results shed light on long-standing problems of the single division potential of precursors and the post-mitotic status of progeny cells. Prospero via regulating Cyclin E in opposite directions at different developmental time points appears to achieve these critical milestones during neurogenesis.
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