Protein expression pattern of the molecular chaperone Mdg1/ERdj4 during embryonic development
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ORIGINAL PAPER
Protein expression pattern of the molecular chaperone Mdg1/ERdj4 during embryonic development Lea Daverkausen‑Fischer1 · Myriam Motyl‑Eisemann2 · Margarethe Draga1 · Martin Scaal1 · Felicitas Pröls1 Accepted: 25 April 2020 © The Author(s) 2020
Abstract The vertebrate-specific co-chaperone Mdg1/ERdj4, which is localized in the endoplasmic reticulum, controls the folding and degradation of proteins. We characterized its protein pattern during chick embryonic development. During early development, Mdg1/ERdj4 protein is present in mesenchymal and epithelial cells. In mesenchymal cells, it has a salt and pepper pattern. In contrast, during epithelial tissue differentiation, Mdg1/ERdj4 marks the basal and/or apical compartment of epithelial linings. The distinct protein pattern in epithelial tissue might point to its role in organizing and maintaining the epithelial structure. This could be achieved, e.g. by controlling folding and secretion of membrane-bound receptors or by inhibiting the IRE1α–Xbp1s–SNAI1/2-induced mesenchymalization. High Mdg1/ERdj4 protein levels are maintained in tissue with sustained secretory activity as in ependymal cells or enterocytes, substantiating its important role for secretion. We conclude that the transient elevation of Mdg1/ERdj4 protein levels controls the differentiation of epithelial linings while constitutive high levels are closely linked to secretory activity. Keywords Molecular chaperone · Hsp40 protein · Mdg1/ERdj4/mDjB9 · Chick · Mesenchymal–epithelial transition (MET) · Epithelial–mesenchymal transition (EMT)
Introduction Due to their induction in heat-shocked cells, chaperones have originally been described as heat shock proteins (Hsps). We now know that only a subset of chaperones is induced in heat-shocked cells. Chaperones are essential for proper folding of proteins and for degradation of irreversibly denatured proteins. They constitute the protein quality control system in every single cell and are essential for maintenance of the cellular ionic and protein homeostasis. Since the on and offset of protein translation and protein transport processes constantly challenge cellular Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00418-020-01881-x) contains supplementary material, which is available to authorized users. * Felicitas Pröls felicitas.proels@uk‑koeln.de 1
Institute of Anatomy II, University of Cologne, Faculty of Medicine, Joseph‑Stelzmann Str. 9, 50931 Cologne, Germany
Klinikum Leverkusen Klinik für Kinder- und Jugendliche, 51375 Leverkusen, Germany
2
homeostasis, chaperones are also required for a variety of normal cellular processes such as proliferation, cell differentiation and migration. The number of chaperones largely varies in different species. In humans, 13 members of the Hsp70 family and 49 different co-chaperone proteins have been identified until today. It is largely unclear why so many members of the chaperone families exist. Yet, some of them are localized in distinct
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