The nuclear transporter importin 13 is critical for cell survival during embryonic stem cell differentiation

Circular RNA hsa_circ_0081343 modulates trophoblast autophagy through Rbm8a nuclear translocation

INTRODUCTION

Fetal growth restriction (FGR) is a kind of obstetric complication that seriously endangers fetal life. Recent studies reported significant reduction of hsa_circ_0081343 in human placenta developed in FGR and is involved in cell migration, invasion, and apoptosis of trophoblast by acting as microRNA sponges. Autophagy is required for invasion of trophoblast cells and for vascular remodeling during placentation. In this study, we aimed to explore the mechanistic link between hsa_circ_0081343 and autophagy.

METHODS

We investigated the interactions between hsa_circ_0081343 and RNA-binding proteins were studied by RNA pull-down assay, mass spectrometry and RNA immunoprecipitation assay. The mechanism of nuclear translocation of Rbm8a were assessed by reverse transcription-quantitative PCR, Western blot, immunofluorescence and Co-Immunoprecipitation. Western blot, immunofluorescence and transmission electron microscopy were performed to elucidate the mechanism underlying hsa_circ_0081343 and/or Rbm8a mediated regulation of autophagy.

RESULTS

hsa_circ_0081343 served as an RNA-binding protein (RBP) sponge. RNA binding motif protein 8A (Rbm8a) was directly bound to hsa_circ_0081343 in the cytoplasm, while knockdown of hsa_circ_0081343 facilitated Rbm8a localization in the nucleus. We also identified Rbm8a as a potential import cargo for Importin13 (Ipo13), which transported Rbm8a across the nuclear membrane into the nucleus. Ipo13 recognized Rbm8a via a functional nuclear localization signal (NLS). Furthermore, the mechanistic study revealed that hsa_circ_0081343-mediated nuclear translocation of Rbm8a activated trophoblast autophagy.

DISCUSSION

Our results suggest that hsa_circ_0081343 could bind to RBP and the interaction between hsa_circ_0081343 and Rbm8a participate in regulating autophagy. These findings offer novel molecular targets and insights for a potential therapeutic strategy against FGR.

DNA methylation as a potential mediator of the association between indoor air pollution and neurodevelopmental delay in a South African birth cohort

BACKGROUND

Exposure to indoor air pollution during pregnancy has been linked to neurodevelopmental delay in toddlers. Epigenetic modification, particularly DNA methylation (DNAm), may explain this link. In this study, we employed three high-dimensional mediation analysis methods (HIMA, DACT, and gHMA) followed by causal mediation analysis to identify differentially methylated CpG sites and genes that mediate the association between indoor air pollution and neurodevelopmental delay. Analyses were performed using data from 142 mother to child pairs from a South African birth cohort, the Drakenstein Child Health Study. DNAm from cord blood was measured using the Infinium MethylationEPIC and HumanMethylation450 arrays. Neurodevelopment was assessed at age 2 years using the Bayley Scores of Infant and Toddler Development, 3rd edition across four domains (cognitive development, general adaptive behavior, language, and motor function). Particulate matter with an aerodynamic diameter of 10 μm or less (PM₁₀) was measured inside participants' homes during the second trimester of pregnancy.

RESULTS

A total of 29 CpG sites and 4 genes (GOPC, RP11-74K11.1, DYRK1A, RNMT) were identified as significant mediators of the association between PM₁₀ and cognitive neurodevelopment. The estimated proportion mediated (95%-confidence interval) ranged from 0.29 [0.01, 0.86] for cg00694520 to 0.54 [0.11, 1.56] for cg05023582.

CONCLUSIONS

Our findings suggest that DNAm may mediate the association between prenatal PM₁₀ exposure and cognitive neurodevelopment. DYRK1A and several genes that our CpG sites mapped to, including CNKSR1, IPO13, IFNGR1, LONP2, and CDH1, are associated with biological pathways implicated in cognitive neurodevelopment and three of our identified CpG sites (cg23560546 [DAPL1], cg22572779 [C6orf218], cg15000966 [NT5C]) have been previously associated with fetal brain development. These findings are novel and add to the limited literature investigating the relationship between indoor air pollution, DNAm, and neurodevelopment, particularly in low- and middle-income country settings and non-white populations.

Nuclear Transporter IPO13 Is Central to Efficient Neuronal Differentiation

Molecular transport between the nucleus and cytoplasm of the cell is mediated by the importin superfamily of transport receptors, of which the bidirectional transporter Importin 13 (IPO13) is a unique member, with a critical role in early embryonic development through nuclear transport of key regulators, such as transcription factors Pax6, Pax3, and ARX. Here, we examined the role of IPO13 in neuronal differentiation for the first time, using a mouse embryonic stem cell (ESC) model and a monolayer-based differentiation protocol to compare IPO13^−/− to wild type ESCs. Although IPO13^−/− ESCs differentiated into neural progenitor cells, as indicated by the expression of dorsal forebrain progenitor markers, reduced expression of progenitor markers Pax6 and Nestin compared to IPO13^−/− was evident, concomitant with reduced nuclear localisation/transcriptional function of IPO13 import cargo Pax6. Differentiation of IPO13^−/− cells into neurons appeared to be strongly impaired, as evidenced by altered morphology, reduced expression of key neuronal markers, and altered response to the neurotransmitter glutamate. Our findings establish that IPO13 has a key role in ESC neuronal differentiation, in part through the nuclear transport of Pax6.

Importins: Diverse roles in male fertility

Regulated nucleocytoplasmic transport is central to the changes in gene expression that underpin cellular development and homeostasis, including in the testis, and proteins in the importin family are the predominant facilitators of cargo transport through the nuclear envelope. Reports documenting cell-specific profiles of importin transcripts and proteins during spermatogenesis led us to hypothesize that importins facilitate developmental switches in the testis. More recently, importins have been shown to serve additional functions, both inside and outside the nucleus; these include acting as subcellular scaffolding, mediating cellular stress responses, and controlling transcription. This paper seeks to provide an overview and update on the functions of importin proteins, with a focus on testis development and spermatogenesis. We present an extended survey of importins by combining published single cell RNAseq data with immunohistochemistry on developing and adult mouse testes. This approach reinforces and broadens knowledge of importins in biological processes, including in spermatogenesis and during testis development, revealing additional avenues for impactful investigations.