Targeted disruption of Noc4l leads to preimplantation embryonic lethality in mice

Genetic mechanisms of fertilization failure and early embryonic arrest: a comprehensive review

BACKGROUND

Infertility and pregnancy loss are longstanding problems. Successful fertilization and high-quality embryos are prerequisites for an ongoing pregnancy. Studies have proven that every stage in the human reproductive process is regulated by multiple genes and any problem, at any step, may lead to fertilization failure (FF) or early embryonic arrest (EEA). Doctors can diagnose the pathogenic factors involved in FF and EEA by using genetic methods. With the progress in the development of new genetic technologies, such as single-cell RNA analysis and whole-exome sequencing, a new approach has opened up for us to directly study human germ cells and reproductive development. These findings will help us to identify the unique mechanism(s) that leads to FF and EEA in order to find potential treatments.

OBJECTIVE AND RATIONALE

The goal of this review is to compile current genetic knowledge related to FF and EEA, clarifying the mechanisms involved and providing clues for clinical diagnosis and treatment.

SEARCH METHODS

PubMed was used to search for relevant research articles and reviews, primarily focusing on English-language publications from January 1978 to June 2023. The search terms included fertilization failure, early embryonic arrest, genetic, epigenetic, whole-exome sequencing, DNA methylation, chromosome, non-coding RNA, and other related keywords. Additional studies were identified by searching reference lists. This review primarily focuses on research conducted in humans. However, it also incorporates relevant data from animal models when applicable. The results were presented descriptively, and individual study quality was not assessed.

OUTCOMES

A total of 233 relevant articles were included in the final review, from 3925 records identified initially. The review provides an overview of genetic factors and mechanisms involved in the human reproductive process. The genetic mutations and other genetic mechanisms of FF and EEA were systematically reviewed, for example, globozoospermia, oocyte activation failure, maternal effect gene mutations, zygotic genome activation abnormalities, chromosome abnormalities, and epigenetic abnormalities. Additionally, the review summarizes progress in treatments for different gene defects, offering new insights for clinical diagnosis and treatment.

WIDER IMPLICATIONS

The information provided in this review will facilitate the development of more accurate molecular screening tools for diagnosing infertility using genetic markers and networks in human reproductive development. The findings will also help guide clinical practice by identifying appropriate interventions based on specific gene mutations. For example, when an individual has obvious gene mutations related to FF, ICSI is recommended instead of IVF. However, in the case of genetic defects such as phospholipase C zeta1 (PLCZ1), actin-like7A (ACTL7A), actin-like 9 (ACTL9), and IQ motif-containing N (IQCN), ICSI may also fail to fertilize. We can consider artificial oocyte activation technology with ICSI to improve fertilization rate and reduce monetary and time costs. In the future, fertility is expected to be improved or restored by interfering with or supplementing the relevant genes.

Embryonic arrest: causes and implications

PURPOSE OF REVIEW

Embryonic arrest is a key determinant of the number of euploid blastocysts obtained after IVF. Here, we review factors that are implicated in the developmental arrest of preimplantation embryos and their relevance for assisted reproduction outcomes.

RECENT FINDINGS

Among the treatment options available to infertile women, IVF is the one associated with most favorable outcomes. The cumulative pregnancy rates in women undergoing IVF are determined by aneuploidy rate (age), ovarian response to stimulation (ovarian reserve), and the rate of embryo developmental arrest. Mutations in maternal effect genes, especially those encoding for subcortical maternal complex, have been implicated in human embryo developmental arrest. In addition, perturbation of biological processes, such as mitochondrial unfolded protein response and long noncoding RNA regulatory pathways, may play a role. However, how each of these factors contributes to embryos' arrest in different cohorts and age groups has not been determined.

SUMMARY

Arrest of human embryos during preimplantation development is a common occurrence and is partly responsible for the limited number of euploid blastocysts obtained in assisted reproduction cycles. Although genetic and metabolic causes have been implicated, the mechanisms responsible for human embryo developmental arrest remain poorly characterized.

Nucleolar protein NOC4L inhibits tumorigenesis and progression by attenuating SIRT1-mediated p53 deacetylation

SIRT1 is an NAD⁺-dependent deacetylase and plays an important role in the deacetylation of both histone and non-histone proteins. Many studies revealed that SIRT1 is upregulated in a variety of tumors and tightly associated with tumorigenesis and cancer progression, but the detailed underlying mechanism of the biological processes remains unclarified. In the present study, we found a nucleolar protein NOC4L, human ortholog of yeast Noc4p, which is essential for the nuclear export of the ribosomal 40S subunit and could bind to SIRT1 to inhibit SIRT1 mediated deacetylation of p53. NOC4L interacts with SIRT1 in variety of cells under nucleolar stress and directly interacts with SIRT1 in vitro. Furthermore, we determined the C-terminal of NOC4L and the catalytic domain of SIRT1 were required for their interaction. Overexpression of NOC4L did not change the protein levels of SIRT1 or p53, but increased the acetylation of p53 and promoted cell apoptosis. Additionally, NOC4L inhibited tumor cell proliferation in a p53-dependent manner and restrained tumor growth in a nude mice xenograft model. Clinically, colorectal cancer patients with the high expression of NOC4L had a better prognosis as TP53 was normally expressed, but no significant difference was observed in survival with mutant TP53. Taken together, our results identified a novel SIRT1 regulatory protein and broaden our understanding of the molecular mechanism of how nucleolar protein NOC4L regulates p53 under nucleolar stress. This research provides an insight into tumorigenesis and cell self-protection in the early stage of DNA damage.

Macrophage deletion of Noc4l triggers endosomal TLR4/TRIF signal and leads to insulin resistance

In obesity, macrophages drive a low-grade systemic inflammation (LSI) and insulin resistance (IR). The ribosome biosynthesis protein NOC4 (NOC4) mediates 40 S ribosomal subunits synthesis in yeast. Hereby, we reported an unexpected location and function of NOC4L, which was preferentially expressed in human and mouse macrophages. NOC4L was decreased in both obese human and mice. The macrophage-specific deletion of Noc4l in mice displayed IR and LSI. Conversely, Noc4l overexpression by lentivirus treatment and transgenic mouse model improved glucose metabolism in mice. Importantly, we found that Noc4l can interact with TLR4 to inhibit its endocytosis and block the TRIF pathway, thereafter ameliorated LSI and IR in mice.

Genetic causes of preimplantation embryo developmental failure

Embryo development requires orchestrated events, finely regulated at the molecular and cellular level by mechanisms which are progressively emerging from animal studies. With progress in genetic technologies-such as genome editing and single-cell RNA analysis-we can now assess embryo gene expression with increased precision and gain new insights into complex processes until recently difficult to explore. Multiple genes and regulative pathways have been identified for each developmental stage. We have learned that embryos with undisturbed and timely gene expression have higher chances of successful development. For example, selected genes are highly expressed during the first stages, being involved in cell adhesion, cell cycle, and regulation of transcription; other genes are instead crucial for lineage specification and therefore expressed at later stages. Due to ethical constraints, studies on human embryos remain scarce, mainly descriptive, and unable to provide functional evidence. This highlights the importance of animal studies as basic knowledge to test and appraise in a clinical context. In this review, we report on preimplantation development with a focus on genes whose impairment leads to developmental arrest. Preconceptional genetic screening could identify loss-of-function mutations of these genes; thereby, novel biomarkers of embryo quality could be adopted to improve diagnosis and treatment of infertility.

Noc4L-Mediated Ribosome Biogenesis Controls Activation of Regulatory and Conventional T Cells

Regulatory T cell (Treg) activation is crucial for maintaining self-tolerance, but the translational regulation of this process is still poorly understood. Although ribosome biogenesis is considered a housekeeping process, emerging evidence supports the hypothesis that ribosome biogenesis can selectively regulate protein synthesis by tuning translation. Here, we focused on the ribosome biogenesis factor Noc4L, based on the observations that Noc4L is highly expressed in activated Tregs. Conditional Noc4L knockout in Tregs resulted in a lethal autoimmune phenotype resembling Treg-deficient scurfy mice. Interestingly, the Noc4L defect did not globally affect overall protein translation in Tregs but was selectively detrimental to the expression of mRNAs related to Treg activation. These results demonstrate the critical role of Noc4L-mediated ribosome biogenesis in controlling the activation of Tregs and maintaining immune tolerance.