LSM14B is essential for oocyte meiotic maturation by regulating maternal mRNA storage and clearance

Fully grown oocytes remain transcriptionally quiescent, yet many maternal mRNAs are synthesized and retained in growing oocytes. We now know that maternal mRNAs are stored in a structure called the mitochondria associated ribonucleoprotein domain (MARDO). But the components and functions of MARDO remain elusive. Here, we found that LSM14B knockout prevents the proper storage and timely clearance of mRNAs (including Cyclin B1, Btg4, and other mRNAs that are translationally activated during meiotic maturation), specifically by disrupting MARDO assembly during oocyte growth and meiotic maturation. With decreased levels of storage and clearance, the LSM14B knockout oocytes failed to enter meiosis II, ultimately resulting in female infertility. Our results demonstrate the function of LSM14B in MARDO assembly, couple the MARDO with mRNA clearance and oocyte meiotic maturation. WT and LSM14B-none oocytes [GV,MI and 14h after hCG (denoted as MII)stages] for three replicates are performed RNA sequencing.完全成熟的卵母细胞处于转录静默状态，但诸多母源mRNA（maternal mRNA）可在生长阶段的卵母细胞中合成并留存。目前已知母源mRNA储存在一种名为线粒体相关核糖核蛋白结构域（mitochondria associated ribonucleoprotein domain，MARDO）的亚细胞结构中，但该结构的组成成分与具体功能仍未阐明。本研究发现，LSM14B基因敲除会通过破坏卵母细胞生长及减数分裂成熟过程中MARDO的组装，阻碍mRNA（包括细胞周期蛋白B1（Cyclin B1）、Btg4以及其他在减数分裂成熟过程中被翻译激活的mRNA）的正常储存与及时清除。由于mRNA储存与清除能力受损，LSM14B基因敲除的卵母细胞无法进入减数第二次分裂（meiosis II），最终导致雌性不育。本研究结果明确了LSM14B在MARDO组装中的功能，并首次将MARDO与mRNA清除及卵母细胞减数分裂成熟过程建立了功能关联。本研究针对三个生物学重复的野生型（wild type，WT）与LSM14B缺失型卵母细胞，分别在生发泡期（germinal vesicle，GV）、减数分裂I期（metaphase I，MI）以及人绒毛膜促性腺激素（human chorionic gonadotropin，hCG）处理后14小时（标记为MII期）这三个阶段开展了RNA测序（RNA sequencing）。