LIN-41 and OMA ribonucleoprotein complexes mediate a translational repression-to-activation switch controlling oocyte meiotic maturation and the oocyte-to-embryo transition in Caenorhabditis elegans. Caenorhabditis elegans

An extended meiotic prophase is a hallmark of oogenesis. Hormonal signaling activates the CDK1/cyclin B kinase to promote oocyte meiotic maturation, which involves nuclear and cytoplasmic events. Nuclear maturation encompasses nuclear envelope breakdown, meiotic spindle assembly, and chromosome segregation. Cytoplasmic maturation involves major changes in oocyte protein translation and cytoplasmic organelles and is poorly understood. In the nematode Caenorhabditis elegans, sperm release the major sperm protein (MSP) hormone to promote oocyte growth and meiotic maturation. Large translational regulatory ribonucleoprotein (RNP) complexes containing the RNA-binding proteins OMA-1, OMA-2, and LIN-41 regulate meiotic maturation downstream of MSP signaling. To understand the control of translation during meiotic maturation, we purified LIN-41-containing RNPs and characterized their protein and RNA components. Protein constituents of LIN-41 RNPs include essential RNA-binding proteins, the GLD-2 cytoplasmic poly(A) polymerase, the CCR4-NOT deadenylase complex, and translation initiation factors. RNA sequencing defined mRNAs associated with both LIN-41 and OMA-1, as well as sets of mRNAs associated with either LIN-41 or OMA-1. Genetic and genomic evidence suggests that GLD-2, which is a component of LIN-41 RNPs, stimulates the efficient translation of many LIN-41-associated transcripts. We analyzed the translational regulation of two transcripts specifically associated with LIN-41 that encode the RNA regulators SPN-4 and MEG-1. We found that LIN-41 represses translation of spn-4 and meg-1, whereas OMA-1 and OMA-2 promote their expression. Upon their synthesis, SPN-4 and MEG-1 assemble into LIN-41 RNPs prior to their functions in the embryo. This study defines a translational repression-to-activation switch as a key element of cytoplasmic maturation. Overall design: Transcripts present in cell lysates and immunoprecipitates from the OMA-1 and LIN-41 ribonuclear-protein complexes were profiles by RNA-seq in duplicate

延长的减数分裂前期（meiotic prophase）是卵子发生（oogenesis）的标志性特征。激素信号激活细胞周期蛋白依赖性激酶1/细胞周期蛋白B（CDK1/cyclin B）激酶，以促进卵母细胞减数分裂成熟（oocyte meiotic maturation），该过程涵盖核事件与细胞质事件。核成熟包含核膜破裂（nuclear envelope breakdown）、减数分裂纺锤体组装（meiotic spindle assembly）与染色体分离（chromosome segregation）。细胞质成熟则涉及卵母细胞蛋白质翻译与细胞质细胞器的显著变化，其调控机制目前尚不清楚。
在秀丽隐杆线虫（Caenorhabditis elegans）中，精子释放主要精子蛋白（major sperm protein, MSP）以促进卵母细胞生长与减数分裂成熟。包含RNA结合蛋白（RNA-binding proteins）OMA-1、OMA-2与LIN-41的大型翻译调控型核糖核蛋白（translational regulatory ribonucleoprotein, RNP）复合物，在MSP信号下游调控减数分裂成熟。
为解析减数分裂成熟过程中的翻译调控机制，本研究纯化了含有LIN-41的RNP复合物，并对其蛋白质与RNA组分进行了系统表征。LIN-41 RNP复合物的蛋白质组分包括必需RNA结合蛋白、GLD-2细胞质多聚腺苷酸聚合酶（GLD-2 cytoplasmic poly(A) polymerase）、CCR4-NOT脱腺苷酶复合物（CCR4-NOT deadenylase complex）以及翻译起始因子（translation initiation factors）。
RNA测序（RNA sequencing）鉴定出了同时与LIN-41和OMA-1结合的转录本（transcripts），以及仅与LIN-41或仅与OMA-1结合的转录本集合。遗传与基因组学证据（genetic and genomic evidence）表明，作为LIN-41 RNP复合物组分的GLD-2，可高效促进众多LIN-41结合转录本的翻译。
本研究分析了两个仅与LIN-41结合的转录本的翻译调控情况，这两个转录本分别编码RNA调控因子SPN-4与MEG-1。研究发现，LIN-41会抑制spn-4与meg-1的翻译，而OMA-1与OMA-2则会促进二者的表达。在SPN-4与MEG-1合成后，它们会在发挥胚胎功能前组装进入LIN-41 RNP复合物。
本研究明确了“翻译抑制-激活转换”是细胞质成熟的关键调控元件。
实验整体设计：采用重复实验方案，通过RNA测序（RNA-seq）对细胞裂解液以及OMA-1与LIN-41核糖核蛋白复合物的免疫沉淀物中的转录本表达谱进行了检测分析。