The splicing regulator PTBP2 controls a program of embryonic splicing required for neuronal maturation.
The splicing regulator PTBP2 controls a program of embryonic splicing required for neuronal maturation.
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作者：
Li Q;Zheng S;Han A;Lin CH;Stoilov P;Fu XD;Black DL
我们表明，剪接调节PTBP 2控制神经元成熟所必需的遗传程序。发育中的小鼠皮质中PTBP 2的耗尽导致这些组织在出生后的前三周内退化，此时正常皮质扩张并发育成熟的回路。培养的Ptbp 2-/-神经元表现出与野生型相同的初始活力，具有适当的神经突生长和标记物表达。然而，这些突变细胞随后不能成熟，并在培养一周后死亡。转录组范围的分析确定了许多外显子，这些外显子在突变的大脑中具有共同的错误调节模式，其中通常在成人中发现的同种型在发育中的胚胎中过早表达。这些转录本编码影响神经突生长、突触前和突触后组装以及突触传递的蛋白质。我们的研究结果定义了一个新的遗传调控程序，其中PTBP 2的作用是暂时抑制成人蛋白亚型的表达，直到神经元的最终成熟。DOI：http://dx.doi.org/10.7554/eLife.01201.001发育中的大脑内的细胞经历一个延长的成熟期。神经元祖细胞必须首先迁移到大脑内的适当位置，然后发展出长的延伸部分，成为成熟神经元与其他细胞交流所用的轴突和树突。最后，必须建立连接神经元与其他神经元的突触。需要多种机制来确保参与这一过程的所有蛋白质在需要的时间和地点表达。蛋白质的产生始于DNA的一个区域被转录以产生RNA转录物，该RNA转录物由称为外显子的片段组成，这些片段被称为内含子的片段分开。然后，这种转录物经历一个称为剪接的过程，该过程涉及内含子被移除，外显子连接在一起形成可以翻译成蛋白质的信使RNA分子。专门的RNA结合蛋白调节剪接过程，并且大多数RNA转录物经受称为选择性剪接的剪接形式，其允许单个基因表达多于一种信使RNA分子，因此多于一种蛋白质产物。随着脑中的神经元祖细胞被诱导成熟为神经元，许多RNA转录物被认为改变了它们的剪接模式。与此同时，称为PTBP 1的调节RNA结合蛋白的水平降低，称为PTBP 2的相关蛋白的水平增加。现在，Li等人研究了缺乏PTBP 2的突变小鼠，发现出生后通常经历广泛发育的前脑结构在PTBP 2缺失时反而经历组织变性。类似地，当缺乏PTPB 2的神经元在培养物中生长时，它们无法正确发育并死亡。Li等人还发现，来自许多基因的信使RNA在突变小鼠中表现出有缺陷的选择性剪接，这些基因参与了出生后大脑发育的影响过程，如轴突和树突的生长以及突触的形成。具体来说，通常只在成人大脑中表达的蛋白质变体表达得更早。通过抑制成人形式的蛋白质的表达直到神经元成熟，PTBP 2在控制大脑的早期发育中起着至关重要的作用。现在需要进一步的工作来确定PTBP 2控制的信使RNA和蛋白质结构的个体变化如何改变未成熟和成熟神经元之间的蛋白质功能。DOI：http://dx.doi.org/10.7554/eLife.01201.002网站
We show that the splicing regulator PTBP2 controls a genetic program essential for neuronal maturation. Depletion of PTBP2 in developing mouse cortex leads to degeneration of these tissues over the first three postnatal weeks, a time when the normal cortex expands and develops mature circuits. Cultured Ptbp2−/− neurons exhibit the same initial viability as wild type, with proper neurite outgrowth and marker expression. However, these mutant cells subsequently fail to mature and die after a week in culture. Transcriptome-wide analyses identify many exons that share a pattern of mis-regulation in the mutant brains, where isoforms normally found in adults are precociously expressed in the developing embryo. These transcripts encode proteins affecting neurite growth, pre- and post-synaptic assembly, and synaptic transmission. Our results define a new genetic regulatory program, where PTBP2 acts to temporarily repress expression of adult protein isoforms until the final maturation of the neuron. DOI: http://dx.doi.org/10.7554/eLife.01201.001 Cells within the developing brain undergo an extended period of maturation. A neuronal progenitor cell must first migrate to the proper place within the brain and then develop long extensions that become the axon and dendrites used by the mature neuron to communicate with other cells. Finally, the synapses that connect neurons with other neurons must be established. Multiple mechanisms are needed to ensure that all the proteins involved in this process are expressed when and where they are needed. The production of a protein begins with a region of DNA being transcribed to produce an RNA transcript that consists of segments called exons separated by segments called introns. This transcript then undergoes a process called splicing that involves the introns being removed and the exons being joined together to form a messenger RNA molecule that can be translated into protein. Specialized RNA binding proteins regulate the splicing process, and most RNA transcripts are subject to a form of splicing called alternative splicing that allows a single gene to express more than one messenger RNA molecule and hence more than one protein product. As neuronal progenitor cells in the brain are induced to mature into neurons, many RNA transcripts are seen to change their splicing patterns. At the same time, the level of a regulatory RNA binding protein called PTBP1 decreases and the level of a related protein called PTBP2 increases. Now Li et al. have studied mutant mice that lack PTBP2, and have found that structures of the forebrain that normally undergo extensive development after birth instead experience tissue degeneration when PTBP2 is absent. Similarly, when neurons lacking PTPB2 are grown in culture, they fail to develop correctly and die. Li et al. also found that messenger RNAs from many genes involved in postnatal brain development—affecting processes such as the growth of axons and dendrites and the formation of synapses—exhibit defective alternative splicing in the mutant mice. Specifically, protein variants that would normally be expressed only in adult brains were being expressed much earlier. By inhibiting the expression of adult forms of proteins until neurons have matured, PTBP2 plays an essential role in controlling the brain’s early development. Further work is now required to determine how individual changes in messenger RNA and protein structure controlled by PTBP2 might alter protein function between immature and mature neurons. DOI: http://dx.doi.org/10.7554/eLife.01201.002