Knockdown of Toe1 causes developmental arrest during the morula-to-blastocyst transition in mice

Knockdown of Mageb16 disrupts cell proliferation and lineage specification during mouse preimplantation development

Melanoma antigen family member B16 (Mageb16) is crucial for maintaining the pluripotency and differentiation of embryonic stem cells. However, the expression pattern and biological role of Mageb16 during preimplantation development remain unclear. In this study, we showed that Mageb16 mRNA expression was dynamic throughout preimplantation development, with the highest level occurring at the morula stage. The abundance of Mageb16 mRNA was effectively reduced via small interfering RNA (siRNA) microinjection. Mageb16 knockdown significantly reduced the blastocyst formation rate, outgrowth formation rate, and total number of cells per embryo. Importantly, the reduction in MAGEB16 blocked cell cycle progression at the G2/M phase and disrupted lineage segregation but did not induce DNA damage in preimplantation mouse embryos. Intriguingly, Mageb16 knockdown increased the level of histone H3 lysine 27 acetylation (H3K27ac) but attenuated transcriptional activity. Together, our results reveal a crucial role for Mageb16 in mouse preimplantation development, likely by controlling cell proliferation and lineage specification.

BPS causes abnormal blastocyst development by inhibiting cell proliferation

In recent years, the escalating global utilization of bisphenol S (BPS) has raised growing concerns regarding its potential adverse effects on human health. However, the effects of BPS exposure on mammalian embryonic development and the associated molecular mechanisms remain inadequately characterized. In this study, we systematically investigated BPS toxicity in mouse embryogenesis by exposing embryos to graded concentrations (0-25 μg/mL). Our results demonstrated a dose-dependent impairment in early embryonic quality following BPS exposure. Specifically, treatment with 10 μg/mL and 15 μg/mL BPS significantly reduced blastocyst formation rates, diminished implantation potential, decreased total cell number of blastocysts, and caused cell fate determination imbalance. Mechanistic studies revealed that under BPS exposure, the massive accumulation of reactive oxygen species (ROS) in embryos induced cell cycle arrest and enhanced autophagy. It is worth noting that the reduction in the total cell number within blastocysts under BPS exposure manifested independently of the apoptotic pathway, as evidenced by the absence of upregulation in caspase 3/7 activity levels and TUNEL-positive signals. Our data collectively reveal that BPS disrupts early embryogenesis through ROS-driven cell cycle dysregulation and erroneous cell fate determination, culminating in compromised blastocyst developmental competence. This research unveils previously unrecognized mechanisms underlying BPS embryotoxicity, emphasizing essential parameters for evaluating chemical reproductive hazards in safety assessments.

Case report: A severe clinical phenotype of pontocerebellar hypoplasia type 7 with compound heterozygous variants of TOE1

Pontocerebellar Hypoplasia (PCH) is a rare autosomal recessive hereditary neurological degenerative disease. To elaborate upon the clinical phenotypes of PCH and explore the correlation between TOE1 gene mutations and clinical phenotype, we analyze the clinical and genetic features of a Chinese infant afflicted with pontocerebellar dysplasia accompanied by gender reversal with bioinformatics methods. The main clinical features of this infant with TOE1 gene mutation included progressive lateral ventricle widening, hydrocephalus, severe postnatal growth retardation, and hypotonia, and simultaneously being accompanied by 46, XY female sex reversal. Whole exome sequencing revealed a compound heterozygous mutation in the TOE1 gene (c.299T > G, c.1414T > G), with the protein homology modeling-generated structure predicting a pathogenic variation, which is closely related to the clinical manifestations in the patient. The new mutation sites, c.299T > G and c.1414T > G, in the TOE1 gene are pathogenic variants of pontocerebellar hypoplasia type 7.

The PARN, TOE1, and USB1 RNA deadenylases and their roles in non-coding RNA regulation

The levels of non-coding RNAs (ncRNAs) are regulated by transcription, RNA processing, and RNA degradation pathways. One mechanism for the degradation of ncRNAs involves the addition of oligo(A) tails by non-canonical poly(A) polymerases, which then recruit processive sequence-independent 3' to 5' exonucleases for RNA degradation. This pathway of decay is also regulated by three 3' to 5' exoribonucleases, USB1, PARN, and TOE1, which remove oligo(A) tails and thereby can protect ncRNAs from decay in a manner analogous to the deubiquitination of proteins. Loss-of-function mutations in these genes lead to premature degradation of some ncRNAs and lead to specific human diseases such as Poikiloderma with Neutropenia (PN) for USB1, Dyskeratosis Congenita (DC) for PARN and Pontocerebellar Hypoplasia type 7 (PCH7) for TOE1. Herein, we review the biochemical properties of USB1, PARN, and TOE1, how they modulate ncRNA levels, and their roles in human diseases.

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.

Expression patterns and biological function of BCL2L10 during mouse preimplantation development

BCL2-like 10 (BCL2L10) is abundantly expressed in mammalian oocytes and plays a crucial role in the completion of oocyte meiosis. However, the expression patterns of BCL2L10 and its biological functions during preimplantation development have not been well characterized. Here, we investigated the spatiotemporal expressions of Bcl2l10 during mouse preimplantation development using RT-qPCR and immunofluorescence and its biological function using siRNA and morpholino injection into pronuclear embryos. Results from RT-qPCR showed that Bcl2l10 was highly expressed in the metaphase Ⅱ-stage oocytes and pronuclear-stage embryos, but expression markedly decreased from the two-cell stage onwards and was no longer detected at the four-cell stage and beyond. Immunofluorescence staining showed that BCL2L10 was detectable throughout preimplantation development and localized in the cytoplasm and nuclei. Knocking down Bcl2l10 resulted in a reduced blastocyst formation rate (P < 0.01) and decreased expression of OCT4, NANOG, and SOX17 (P < 0.05). We concluded that the role of BCL2L10 is strongly associated with developmental competence of preimplantation mouse embryos.