Abstract
The TFF peptides xP1 and xP4 from Xenopus laevis are orthologs of TFF1 and TFF2, respectively. xP1 is secreted as a monomer from gastric surface mucous cells and is generally not associated with mucins, whereas xP4 is a typical secretory peptide from esophageal goblet cells, and gastric mucous neck and antral gland cells tightly associated as a lectin with the ortholog of mucin MUC6. Both TFF peptides have diverse protective functions, xP1 as a scavenger for reactive oxygen species preventing oxidative damage and xP4 as a constituent of the water-insoluble adherent inner mucus barrier. Here, we present localization studies using immunofluorescence and immunoelectron microscopy. xP1 is concentrated in dense cores of secretory granules of surface mucous cells, whereas xP4 mixes with MUC6 in esophageal goblet cells. Of note, we observe two different types of goblet cells, which differ in their xP4 synthesis, and this is even visible morphologically at the electron microscopic level. xP4-negative granules are recognized by their halo, which is probably the result of shrinkage during the processing of samples for electron microscopy. Probably, the tight lectin binding of xP4 and MUC6 creates a crosslinked mucous network forming a stabile granule matrix, which prevents shrinkage.
Highlights
The secretory peptides xP1 and xP4 belong to the family of trefoil factor family (TFF) peptides and represent the Xenopus laevis orthologs of mammalian TFF1 and TFF2, respectively [1,2,3]
The TFF peptides xP1 and xP4 from Xenopus laevis are orthologs of TFF1 and TFF2, respectively. xP1 is secreted as a monomer from gastric surface mucous cells and is generally not associated with mucins, whereas xP4 is a typical secretory peptide from esophageal goblet cells, and gastric mucous neck and antral gland cells tightly associated as a lectin with the ortholog of mucin MUC6
We present localization studies using immunofluorescence and immunoelectron microscopy. xP1 is concentrated in dense cores of secretory granules of surface mucous cells, whereas xP4 mixes with MUC6 in esophageal goblet cells
Summary
The secretory peptides xP1 and xP4 belong to the family of trefoil factor family (TFF) peptides and represent the Xenopus laevis orthologs of mammalian TFF1 and TFF2, respectively [1,2,3]. TFF peptides contain a cysteine-rich module containing six disulfide-linked cysteine residues [4]. This peptide family plays a role in the protection of mucosal epithelia [4,5,6]. The subgenomes evolved asymmetrically [10] This might be the reason why the expression of xP4.1 and xP4.2 differs characteristically: xP4.1 is synthesized with an increasing gradient from the gastric fundus to the antrum and weakly persists even into the anterior part of the intestine, but is not expressed in the esophagus [3,7,9]. XP4.2 is expressed in the esophagus with a decreasing gradient from the gastric fundus to the antrum [3,7,9]
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