During mammalian oocyte growth, chromatin configuration transition from the nonsurrounded nucleolus (NSN) to surrounded nucleolus (SN) type plays a key role in the regulation of gene expression and acquisition of meiotic and developmental competence by the oocyte. Nonetheless, the mechanism underlying chromatin configuration maturation in oocytes is poorly understood. Here we show that nucleolar protein DCAF13 is an important component of the ribosomal RNA (rRNA)-processing complex and is essential for oocyte NSN-SN transition in mice. A conditional knockout of Dcaf13 in oocytes led to the arrest of oocyte development in the NSN configuration, follicular atresia, premature ovarian failure, and female sterility. The DCAF13 deficiency resulted in pre-rRNA accumulation in oocytes, whereas the total mRNA level was not altered. Further exploration showed that DCAF13 participated in the 18S rRNA processing in growing oocytes. The lack of 18S rRNA because of DCAF13 deletion caused a ribosome assembly disorder and then reduced global protein synthesis. DCAF13 interacted with a protein of the core box C/D ribonucleoprotein, fibrillarin, i.e., a factor of early pre-rRNA processing. When fibrillarin was knocked down in the oocytes from primary follicles, follicle development was inhibited as well, indicating that an rRNA processing defect in the oocyte indeed stunts chromatin configuration transition and follicle development. Taken together, these results elucidated the in vivo function of novel nucleolar protein DCAF13 in maintaining mammalian oogenesis.

Early embryonic arrest and fragmentation (EEAF) is a common phenomenon leading to female infertility, but the genetic determinants remain largely unknown. The Moloney sarcoma oncogene (MOS) encodes a serine/threonine kinase that activates the ERK signaling cascade during oocyte maturation in vertebrates. Here, we identified four rare variants of MOS in three infertile female individuals with EEAF that followed a recessive inheritance pattern. These MOS variants encoded proteins that resulted in decreased phosphorylated ERK1/2 level in cells and oocytes, and displayed attenuated rescuing effects on cortical F‐actin assembly. Using oocyte‐specific Erk1/2 knockout mice, we verified that MOS‐ERK signal pathway inactivation in oocytes caused EEAF as human. The RNA sequencing data revealed that maternal mRNA clearance was disrupted in human mature oocytes either with MOS homozygous variant or with U0126 treatment, especially genes relative to mitochondrial function. Mitochondrial dysfunction was observed in oocytes with ERK1/2 deficiency or inactivation. In conclusion, this study not only uncovers biallelic MOS variants causes EEAF but also demonstrates that MOS‐ERK signaling pathway drives human oocyte cytoplasmic maturation to prevent EEAF.

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Mammalian oocyte maturation is driven by strictly regulated polyadenylation and translational activation of maternal mRNA stored in the cytoplasm. However, the poly(A) polymerase (PAP) that directly mediates cytoplasmic polyadenylation in mammalian oocytes has not been determined. In this study, we identified PAPα as the elusive enzyme that catalyzes cytoplasmic mRNA polyadenylation implicated in mouse oocyte maturation. PAPα was mainly localized in the germinal vesicle (GV) of fully grown oocytes but was distributed to the ooplasm after GV breakdown. Inhibition of PAPα activity impaired cytoplasmic polyadenylation and translation of maternal transcripts, thus blocking meiotic cell cycle progression. Once an oocyte resumes meiosis, activated CDK1 and ERK1/2 cooperatively mediate the phosphorylation of three serine residues of PAPα, 537, 545 and 558, thereby leading to increased activity. This mechanism is responsible for translational activation of transcripts lacking cytoplasmic polyadenylation elements in their 3′-untranslated region (3′-UTR). In turn, activated PAPα stimulated polyadenylation and translation of the mRNA encoding its own (Papola) through a positive feedback circuit. ERK1/2 promoted Papola mRNA translation in a 3′-UTR polyadenylation signal-dependent manner. Through these mechanisms, PAPα activity and levels were significantly amplified, improving the levels of global mRNA polyadenylation and translation, thus, benefiting meiotic cell cycle progression.

Nowadays, although single-cell multi-omics technologies are undergoing rapid development, simultaneous transcriptome and proteome analysis of a single-cell individual still faces great challenges. Here, we developed a single-cell simultaneous transcriptome and proteome (scSTAP) analysis platform based on microfluidics, high-throughput sequencing and mass spectrometry technology, to achieve deep and joint quantitative analysis of transcriptome and proteome at the single-cell level for the first time. This platform was applied to analyze single mouse oocytes at different meiotic maturation stages, reaching an average quantification depth of 19948 genes and 2663 protein groups in single mouse oocytes. This reliable quantitative two-omics dataset of single cells provided an important resource for understanding the relationship between the transcriptome and the proteome in cells. Based on the correlation analysis of RNAs and proteins in the same single cell, we demonstrated the expressive heterogeneity of transcriptome and proteome during the cellular biological process. Specially, we analyzed the meiosis regulatory network during oocyte maturation with an unprecedented depth at the single-cell level, and identified 30 transcript-protein pairs as specific oocyte maturational signatures, providing crucial insights into the regulatory features of transcription and translation during oocyte meiotic maturation.