Project description:The transition from a transcriptionally active state (GV) to a transcriptionally inactive state (mature MII oocytes) is one of the requirements for the acquisition of oocyte developmental competence. After maturation, oocytes are mostly transcriptionally quiescent, and developmental competence prior to embryonic genome activation (EGA) relies on maternal RNA and proteins. The landscape of expressed genes at the MII stage could be mostly driven by post-transcriptional mechanisms, such as alternative splicing (AS). With the development of single cell transcriptome analysis, genome wide AS analysis becomes technically feasible and available to fully characterize the AS patterns in human oocytes. Profiling spliced mRNA isoforms might provide novel information on the molecular mechanisms driving early development, and might be a source of potential biomarkers of oocyte quality. The goal of the present study is to perform a transcriptomic analysis in oocytes at different stages of maturation, to identify the profiles of alternative spliced isoforms produced in both oocyte’ stages.
Project description: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
Project description:Oocyte maturation refers to oocytes at the germinal vesicle stage progressing into metaphase II (MII) stage of development. Even though numerous studies have shown key genes and potential important signalling cascades, which drive the GV to MII transition, a system-wide analysis of underlying differences at gene level and especially at transcript level between the two developmental stages of the oocyte is still lacking. For this, we profiled and analysed RNA from pig oocytes across meiotic maturation (GV, MII and damaged, n=15). We detected 22,516 genes for each sample across meiotic maturation. Principal Component analysis of the data clustered the samples in three stages of development (GV, MII and damaged). Differential expression of genes between the three stages will then be used to delineate the pathways which are up-/down-regulated during these developmental stages. Besides, differential transcript usage will be used to identify the difference of oocytes at distinct developmental stages at isoform level, which might be ignored by traditional differential gene expression analysis.
Project description: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.
Project description:The genetic causes of oocyte meiotic deficiency (OMD), a form of primary infertility characterised by the production of immature oocytes, remain largely unexplored. Using whole exome sequencing, we found that 26% of a cohort of 23 subjects with OMD harboured the same homozygous nonsense pathogenic mutation in PATL2, a gene encoding a putative RNA-binding protein. Using Patl2 knockout mice, we confirmed that PATL2 deficiency disturbs oocyte maturation, since oocytes and zygotes exhibit morphological and developmental defects respectively. PATL2's amphibian orthologue is involved in the regulation of oocyte mRNA as a partner of CPEB. However, Patl2's expression profile throughout oocyte development in mice, alongside colocalisation experiments with Cpeb1, Msy2 and Ddx6 (three oocyte RNA-regulators) suggest an original role for Patl2 in Mammals. Accordingly, transcriptomic analysis of oocytes from WT and Patl2-/- animals demonstrated that in the absence of Patl2, expression levels of a select number of highly relevant genes involved in oocyte maturation and early embryonic development are deregulated. In conclusion, PATL2 is a novel actor of mammalian oocyte maturation whose invalidation causes OMD in humans.
Project description: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.
Project description: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.
Project description:SIRT6, the sixth member of sirtuin family proteins, has been identified as a crucial regulator in multiple molecular pathways related to aging, including genome stability, DNA damage repair, telomere maintenance and inflammation. However, the exact roles of SIRT6 during mammalian oocyte meiosis have not yet fully clarified. Here, we investigated the critical events during porcine oocyte meiotic maturation with the treatment of SIRT6 specific inhibitor SIRT6-IN-1. We found that SIRT6 inhibition resulted in oocyte meiotic failure by displaying the poor expansion of cumulus cells and reduced rate of polar body extrusion. Meanwhile, the compromised spindle assembly, chromosome alignment and actin dynamics were also observed in SIRT6-inhibited oocytes. Moreover, inhibition of SIRT6 led to the defective cytoplasmic maturation by showing the abnormal distribution of cortical granules and their component ovastacin. Notably, we identified that expression of genes related to oocyte meiosis, oxidative phosphorylation and cellular senescence was remarkably altered in SIRT6-inhibited oocytes by transcriptome analysis, and validated that the meiotic defects caused by SIRT6 inhibition resulted from the excessive ROS-induced early apoptosis in oocytes. Taken together, our findings demonstrate that SIRT6 promotes the porcine oocyte meiotic maturation via maintaining the organelle dynamics.