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.

中文翻译：

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分子伴侣Mdg1 / ERdj4在胚胎发育过程中的蛋白质表达模式。

脊椎动物特有的伴侣蛋白Mdg1 / ERdj4位于内质网中，控制着蛋白质的折叠和降解。我们在雏鸡胚胎发育过程中表征了其蛋白质模式。在早期发育期间，Mdg1 / ERdj4蛋白存在于间充质和上皮细胞中。在间质细胞中，它具有盐和胡椒的模式。相反，在上皮组织分化过程中，Mdg1 / ERdj4标志着上皮衬里的基底和/或根尖室。上皮组织中独特的蛋白质模式可能表明其在组织和维持上皮结构中的作用。例如，可以通过控制膜结合受体的折叠和分泌，或者通过抑制IRE1α-Xbp1s-SNAI1/ 2诱导的间充质化来实现。高Mdg1 / ERdj4蛋白水平在具有持续分泌活性的组织中保持不变，如在室管膜细胞或肠上皮细胞中，证实了其在分泌中的重要作用。我们得出结论，Mdg1 / ERdj4蛋白水平的短暂升高控制了上皮内衬的分化，而组成型高水平与分泌活性密切相关。