The CCR4-NOT complex suppresses untimely translational activation of maternal mRNAs

Characterization of OsCAF1 Protein Function in Rice Response to Thermal Stress

Heat stress is a critical environmental challenge that disrupts rice growth, development, and productivity and poses a significant threat to global food security. The CCR4-NOT protein complex, particularly its CCR4-associated factor 1 (CAF1) subunit, plays a crucial role in the dynamic regulation of gene expression by mediating mRNA de-adenylation, a key step in mRNA degradation and turnover. However, the specific function of OsCAF1 proteins under heat stress in rice remains poorly understood. In this study, we investigated the dynamic subcellular localization of OsCAF1A in response to elevated temperatures and its role in heat stress tolerance. Under normal conditions, OsCAF1A is diffusely localized to the cytoplasm. However, OsCAF1A predominantly localizes to processing bodies (PBs) under heat stress. The results of interaction studies revealed that two DEAD-box RNA helicases, OseIF4AIIb and OsRH8, modulate the re-localization of OsCAF1A, by OseIF4AIIb inhibiting and OsRH8 promoting its association with PBs during heat stress. Furthermore, OsCAF1A mRNA was more abundantly expressed in rice seedlings than other OsCAF1 genes and is further upregulated by high temperature. The overexpression of OsCAF1A significantly enhanced heat tolerance, whereas mutants exhibited increased heat sensitivity. These findings underscore the potential of OsCAF1A as a tool to improve crop resilience to climate change.

Genetic Abnormalities of Oocyte Maturation: Mechanisms and Clinical Implications

Genetic anomalies in oocyte maturation present significant fertility and embryonic development challenges. This review explores the intricate mechanisms of nuclear and cytoplasmic maturation, emphasizing the genetic and molecular factors contributing to oocyte quality and competence. Chromosomal mutations, errors in segregation, genetic mutations in signaling pathways and meiosis-related genes, and epigenetic alterations are discussed as critical contributors to oocyte maturation defects. The role of mitochondrial defects, maternal mRNA dysregulation, and critical proteins such as NLRP14 and BMP6 are highlighted. Understanding these genetic factors is crucial for improving diagnostic approaches and therapeutic interventions in reproductive medicine, particularly for couples encountering recurrent in vitro fertilization failures. This review will explore how specific genetic mutations impact fertility treatments and reproductive success by examining the intricate oocyte maturation process. We will focus on genetic abnormalities that may disrupt the oocyte maturation pathway, discussing the underlying mechanisms involved and considering their potential clinical implications for enhancing fertility outcomes.

CtIP regulates G2/M transition and bipolar spindle assembly during mouse oocyte meiosis

CtBP-interacting protein (CtIP) is known for its multifaceted roles in DNA repair and genomic stability, directing the homologous recombination-mediated DNA double-stranded break repair pathway via DNA end resection, an essential error-free repair process vital for genome stability. Mammalian oocytes are highly prone to DNA damage accumulation due to prolonged G2/prophase arrest. Here, we explore the functions of CtIP in meiotic cell cycle regulation via a mouse oocyte model. Depletion of CtIP by siRNA injection results in delayed germinal vesicle breakdown and failed polar body extrusion. Mechanistically, CtIP deficiency increases DNA damage and decreases the expression and nuclear entry of CCNB1, resulting in marked impairment of meiotic resumption, which can be rescued by exogenous CCNB1 overexpression. Furthermore, depletion of CtIP disrupts microtubule-organizing centers coalescence at spindle poles as indicated by failed accumulation of γ-tubulin, p-Aurora kinase A, Kif2A, and TPX2, leading to abnormal spindle assembly and prometaphase arrest. These results provide valuable insights into the important roles of CtIP in the G2/M checkpoint and spindle assembly in mouse oocyte meiotic cell cycle regulation.

The molecular mechanisms underpinning maternal mRNA dormancy

A large number of mRNAs of maternal origin are produced during oogenesis and deposited in the oocyte. Since transcription stops at the onset of meiosis during oogenesis and does not resume until later in embryogenesis, maternal mRNAs are the only templates for protein synthesis during this period. To ensure that a protein is made in the right place at the right time, the translation of maternal mRNAs must be activated at a specific stage of development. Here we summarize our current understanding of the sophisticated mechanisms that contribute to the temporal repression of maternal mRNAs, termed maternal mRNA dormancy. We discuss mechanisms at the level of the RNA itself, such as the regulation of polyadenine tail length and RNA modifications, as well as at the level of RNA-binding proteins, which often block the assembly of translation initiation complexes at the 5' end of an mRNA or recruit mRNAs to specific subcellular compartments. We also review microRNAs and other mechanisms that contribute to repressing translation, such as ribosome dormancy. Importantly, the mechanisms responsible for mRNA dormancy during the oocyte-to-embryo transition are also relevant to cellular quiescence in other biological contexts.

Regulation of Oocyte mRNA Metabolism: A Key Determinant of Oocyte Developmental Competence

The regulation of mRNA transcription and translation is uncoupled during oogenesis. The reason for this uncoupling is two-fold. Chromatin is only accessible to the transcriptional machinery during the growth phase as it condenses prior to resumption of meiosis to ensure faithful segregation of chromosomes during meiotic maturation. Thus, transcription rates are high during this time period in order to produce all of the transcripts needed for meiosis, fertilization, and embryo cleavage until the newly formed embryonic genome becomes transcriptionally active. To ensure appropriate timing of key developmental milestones including chromatin condensation, resumption of meiosis, segregation of chromosomes, and polar body extrusion, the translation of protein from transcripts synthesized during oocyte growth must be temporally regulated. This is achieved by the regulation of mRNA interaction with RNA binding proteins and shortening and lengthening of the poly(A) tail. This chapter details the essential factors that regulate the dynamic changes in mRNA synthesis, storage, translation, and degradation during oocyte growth and maturation.