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      Neuraxial dysraphism in EPAS1-associated syndrome due to improper mesenchymal transition

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          Abstract

          Objective

          To investigate the effect of somatic, postzygotic, gain-of-function mutation of Endothelial Per-Arnt-Sim (PAS) domain protein 1 ( EPAS1) encoding hypoxia-inducible factor-2α (HIF-2α) on posterior fossa development and spinal dysraphism in EPAS1 gain-of-function syndrome, which consists of multiple paragangliomas, somatostatinoma, and polycythemia.

          Methods

          Patients referred to our institution for evaluation of new, recurrent, and/or metastatic paragangliomas/pheochromocytoma were confirmed for EPAS1 gain-of-function syndrome by identification of the EPAS1 gain-of-function mutation in resected tumors and/or circulating leukocytes. The posterior fossa, its contents, and the spine were evaluated retrospectively on available MRI and CT images of the head and neck performed for tumor staging and restaging. The transgenic mouse model underwent Microfil vascular perfusion and subsequent intact ex vivo 14T MRI and micro-CT as well as gross dissection, histology, and immunohistochemistry to assess the role of EPAS1 in identified malformations.

          Results

          All 8 patients with EPAS1 gain-of-function syndrome demonstrated incidental posterior fossa malformations—one Dandy-Walker variant and 7 Chiari malformations without syringomyelia. These findings were not associated with a small posterior fossa; rather, the posterior fossa volume exceeded that of its neural contents. Seven of 8 patients demonstrated spinal dysraphism; 4 of 8 demonstrated abnormal vertebral segmentation. The mouse model similarly demonstrated features of neuraxial dysraphism, including cervical myelomeningocele and spinal dysraphism, and cerebellar tonsil displacement through the foramen magnum. Histology and immunohistochemistry demonstrated incomplete mesenchymal transition in the mutant but not the control mouse.

          Conclusions

          This study characterized posterior fossa and spinal malformations seen in EPAS1 gain-of-function syndrome and suggests that gain-of-function mutation in HIF-2α results in improper mesenchymal transition.

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          Most cited references 31

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          Efficient in vivo manipulation of mouse genomic sequences at the zygote stage.

          We describe a transgenic mouse line carrying the cre transgene under the control of the adenovirus EIIa promoter that targets expression of the Cre recombinase to the early mouse embryo. To assess the ability of this recombinase to excise loxP-flanked DNA sequences at early stages of development, we bred EIIa-cre transgenic mice to two different mouse lines carrying loxP-flanked target sequences: (i) a strain with a single gene-targeted neomycin resistance gene flanked by 1oxP sites and (ii) a transgenic line carrying multiple transgene copies with internal loxP sites. Mating either of these loxP-carrying mouse lines to EIIa-cre mice resulted in first generation progeny in which the loxP-flanked sequences had been efficiently deleted from all tissues tested, including the germ cells. Interbreeding of these first generation progeny resulted in efficient germ-line transmission of the deletion to subsequent generations. These results demonstrate a method by which loxP-flanked DNA sequences can be efficiently deleted in the early mouse embryo. Potential applications of this approach are discussed, including reduction of multicopy transgene loci to produce single-copy transgenic lines and introduction of a variety of subtle mutations into the line.
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            The role of hypoxia in development of the Mammalian embryo.

            Hypoxia inducible factor (HIF) is a transcription factor that acts in low-oxygen conditions. The cellular response to HIF activation is transcriptional upregulation of a large group of genes. Some target genes promote anaerobic metabolism to reduce oxygen consumption, while others "alleviate" hypoxia by acting non-cell-autonomously to extend and modify the surrounding vasculature. Although hypoxia is often thought of as being a pathological phenomenon, the mammalian embryo in fact develops in a low-oxygen environment, and in this context HIF has additional responsibilities. This review describes how low oxygen and HIF affect gene expression, cell behavior, and ultimately morphogenesis of the embryo and placenta. 2009 Elsevier Inc. All rights reserved.
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              Somatic HIF2A gain-of-function mutations in paraganglioma with polycythemia.

              Hypoxia-inducible factors are transcription factors controlling energy, iron metabolism, erythropoiesis, and development. When these proteins are dysregulated, they contribute to tumorigenesis and cancer progression. However, mutations in genes encoding α subunits of hypoxia-inducible factors (HIF-α) have not previously been identified in any cancer. Here we report two novel somatic gain-of-function mutations in the gene encoding hypoxia-inducible factor 2α (HIF2A) in two patients, one presenting with paraganglioma and the other with paraganglioma and somatostatinoma, both of whom had polycythemia. The two mutations were associated with increased HIF-2α activity and increased protein half-life.
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                Author and article information

                Journal
                Neurol Genet
                Neurol Genet
                nng
                NNG
                Neurology: Genetics
                Wolters Kluwer (Baltimore )
                2376-7839
                June 2020
                1 April 2020
                1 April 2020
                : 6
                : 3
                Affiliations
                From the National Institutes of Health (J.S.R., A.J.C., H.W., Z.Z.), National Cancer Institute Neuro-Oncology Branch; National Institutes of Health (D.P.A., J.D.H.), National Institute of Neurological Disorders and Stroke, Surgical Neurology Branch; National Institutes of Health (Y.P., A.J., K.P.), Eunice Kennedy Shriver National Institute of Child Health and Human Development, Section on Medical Neuroendocrinology; Georgetown Hospital (M.A.N.), Internal Medicine and Pediatrics, Washington DC; National Institutes of Health (J.P.M., D.R.D.), National Institute of Neurological Disorders and Stroke, Mouse Imaging Facility, Bethesda, MD; George Washington University (J.G.S.), Radiology, Washington DC; National Library of Medicine (J.G.S.), MedPix®; National Institutes of Health (M.M.M.), Center for Cancer Research, National Cancer Institute, Laboratory of Pathology; and National Institutes of Health (R.H.K., B.A.K.), National Heart Lung and Blood Institute, Translational Vascular Medicine Branch, Bethesda, MD.
                Author notes
                Correspondence Dr. Heiss heissj@ 123456ninds.nih.gov

                Go to Neurology.org/NG for full disclosures. Funding information is provided at the end of the article.

                The Article Processing Charge was funded by NIH.

                [*]

                These authors contributed equally to the manuscript.

                Article
                NG2019012096
                10.1212/NXG.0000000000000414
                7164966
                Copyright © 2020 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Neurology.

                This is an open access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND), which permits downloading and sharing the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal.

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