Membrane integrity at the endoplasmic reticulum (ER) is tightly regulated, and its disturbance is implicated in metabolic diseases. Using an engineered sensor that activates the unfolded protein response (UPR) exclusively when normal ER membrane lipid composition is compromised, we identified pathways beyond lipid metabolism that are necessary to maintain ER integrity in yeast and in C. elegans. To systematically validate yeast mutants that disrupt ER membrane homeostasis, we identified a lipid bilayer stress (LBS) sensor in the UPR transducer protein Ire1, located at the interface of the amphipathic and transmembrane helices. Furthermore, transcriptome and chromatin immunoprecipitation analyses pinpoint the UPR as a broad-spectrum compensatory response wherein LBS and proteotoxic stress deploy divergent transcriptional UPR programs. Together, these findings reveal the UPR program as the sum of two independent stress responses, an insight that could be exploited for future therapeutic intervention.

Biological membranes are not only essential barriers that separate cellular and subcellular structures, but also perform other critical functions such as the initiation and propagation of intra- and intercellular signals. Each membrane-delineated organelle has a tightly regulated and custom-made membrane lipid composition that is critical for its normal function. The endoplasmic reticulum (ER) consists of a dynamic membrane network that is required for the synthesis and modification of proteins and lipids. The accumulation of unfolded proteins in the ER lumen activates an adaptive stress response known as the unfolded protein response (UPR-ER). Interestingly, recent findings show that lipid perturbation is also a direct activator of the UPR-ER, independent of protein misfolding. Here, we review proteostasis-independent UPR-ER activation in the genetically tractable model organism Caenorhabditis elegans. We review the current knowledge on the membrane lipid composition of the ER, its impact on organelle function and UPR-ER activation, and its potential role in human metabolic diseases. Further, we summarize the bi-directional interplay between lipid metabolism and the UPR-ER. We discuss recent progress identifying the different respective mechanisms by which disturbed proteostasis and lipid bilayer stress activate the UPR-ER. Finally, we consider how genetic and metabolic disturbances may disrupt ER homeostasis and activate the UPR and discuss how using -omics-type analyses will lead to more comprehensive insights into these processes.

SUMMARYMembrane integrity at the endoplasmic reticulum (ER) is tightly regulated and is implicated in metabolic diseases when compromised. Using an engineered sensor that exclusively activates the unfolded protein response (UPR) during aberrant ER membrane lipid composition, we identified pathways beyond lipid metabolism that are necessary to maintain ER integrity in yeast and are conserved in C. elegans. To systematically validate yeast mutants disrupting ER membrane homeostasis, we identified a lipid bilayer stress (LBS) sensing switch in the UPR transducer protein Ire1, located at the interface of the amphipathic and transmembrane helices. Furthermore, transcriptome and chromatin immunoprecipitation (ChIP) analyses pinpoint the UPR as a broad-spectrum compensatory pathway in which LBS and proteotoxic stress-induced UPR deploy divergent transcriptional programs. Together, these findings reveal the UPR program as the sum of two independent stress events and could be exploited for future therapeutic intervention.

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Objective: To describe clinicoradiological features and outcomes of reversible splenial lesion syndrome (RESLES) in children. Methods: Data from 23 children (25 RESLES episodes; two patients had recurring episodes) was retrospectively reviewed at the

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Neural tube defects (NTDs) are the most serious and common birth defects in the clinical setting. The Notch signaling pathway has been implicated in different processes of the embryonic neural stem cells (NSCs) during neural tube development. The aim of the present study was to investigate the expression pattern and function of Notch1 (N1) in all-trans retinoic acid (atRA)-induced NTDs and NSC differentiation. A mouse model of brain abnormality was established by administering 28 mg/kg atRA, and then brain development was examined using hematoxylin and eosin (H&E) staining. The N1 expression pattern was detected in the brain of mice embryos via immunohistochemistry and western blotting. NSCs were extracted from the fetal brain of C57 BL/6 embryos at 18.5 days of pregnancy. N1, Nestin, neurofilament (NF), glial fibrillary acidic protein (GFAP) and galactocerebroside (GALC) were identified using immunohistochemistry. Moreover, N1, presenilin 1 (PS1), Nestin, NF, GFAP and GALC were detected via western blotting at different time points in the NSCs with control media or atRA media. H&E staining identified that the embryonic brain treated with atRA was more developed compared with the control group. N1 was downregulated in the embryonic mouse brain between days 11 and 17 in the atRA-treated group compared with the untreated group. The distribution of N1, Nestin, NF, GFAP and GALC was positively detected using immunofluorescence staining. Western blotting results demonstrated that there were significantly, synchronous decreased expression levels of N1 and PS1, but increased expression levels of NF, GFAP and GALC in NSCs treated with atRA compared with those observed in the controls (P<0.05). The results suggested that the N1 signaling pathway inhibited brain development and NSC differentiation. Collectively, it was found that atRA promoted mouse embryo brain development and the differentiation of NSCs by inhibiting the N1 pathway.