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

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.