DIS3L2 clears terminal-uridylated RNA to ensure oocyte maturation and female fertility

During mammalian oocyte development, transcriptome undergoes accumulation in the oocyte growth phase and elimination in the oocyte maturation phase. At the transition point between growth and maturation, which is the germinal vesicle intact oocyte (GV), terminal uridylation labels RNA for degradation. In our study, we show that a small cohort of RNA are polyadenylated after tail uridylation (defined as uridylated-poly(A) RNA). Upon genetic depletion of DIS3L2 (Dis3l2cKO) in mouse oocytes, uridylated-poly(A) RNA is extensively stabilized and dominates the oocyte transcriptome, which results in increased transcriptome in Dis3l2cKO oocytes. Consequently, Dis3l2cKO female mice are infertile and almost all oocytes are arrested at the GV stage. Uridylated-poly(A) RNA generally has shorter poly(A) tails and lower translation activity. The uridylated-poly(A) RNA in Dis3l2cKO oocytes not only generates from the insufficient RNA degradation, but also comes from the tail dynamics of RNA. Our study demonstrates more possibilities of RNA fates after being terminally uridylated, and highlights the role of DIS3L2 in safeguarding the transcriptome by degrading uridylated-poly(A) RNA. Overall design: We performed transcriptome profiling using single oocyte RNA-seq (polyA RNA and total RNA) and single oocyte PAIso-seq. The single oocyte RNA-seq is done at GV and MII stages and the PAIso-seq is done at the GV stage.

在哺乳动物卵母细胞发育过程中，转录组会在卵母细胞生长阶段发生积累，而在卵母细胞成熟阶段被清除。在生长与成熟的过渡节点——生发泡完整卵母细胞（germinal vesicle intact oocyte, GV）——中，末端尿苷酰化会标记RNA并使其进入降解途径。本研究发现，有一小群RNA会在尾部发生尿苷酰化后再进行多聚腺苷酸化，这类RNA被定义为尿苷酰化-多聚腺苷酸化RNA（uridylated-poly(A) RNA）。在小鼠卵母细胞中条件性敲除DIS3L2（Dis3l2cKO）后，尿苷酰化-多聚腺苷酸化RNA会被广泛稳定，并在卵母细胞转录组中占据主导地位，最终导致Dis3l2cKO卵母细胞的转录组总量升高。因此，Dis3l2cKO雌性小鼠表现为不育，且其几乎所有卵母细胞均停滞在GV期。尿苷酰化-多聚腺苷酸化RNA通常具有更短的多聚(A)尾，且翻译活性更低。Dis3l2cKO卵母细胞中的尿苷酰化-多聚腺苷酸化RNA，不仅源于RNA降解不足，还来自RNA的尾部动态变化过程。本研究揭示了RNA在末端尿苷酰化后更多的命运走向，并阐明了DIS3L2通过降解尿苷酰化-多聚腺苷酸化RNA，以维持卵母细胞转录组稳态的重要作用。实验设计：本研究采用单细胞卵母细胞RNA测序（polyA RNA与总RNA）及单细胞卵母细胞PAIso-seq技术开展转录组图谱分析。其中，单细胞卵母细胞RNA测序覆盖GV期与MII期卵母细胞，而PAIso-seq仅针对GV期卵母细胞。