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The dermal granular glands of the South African clawed frog, Xenopus laevis, contain antimicrobial peptides (AMPs) that are secreted following local nerve stimulation. These natural antibiotics are active against bacteria and fungi including Batrachochytrium dendrobatidis, a fungal pathogen that causes the skin disease chytridiomycosis. Granular gland secretion can be stimulated in the laboratory by norepinephrine injection. We found that two injections of 80nmol/g norepinephrine were necessary to fully deplete the AMP stores. One injection resulted in the secretion of most of the stored peptides. A second injection, 2 days later, released a small amount of additional AMPs that are not compositionally different from those released by the first injection. A third injection, 4 days after the first, did not result in further AMP release. Mass spectrometry and histology confirmed that glands are depleted after two injections. Periodic acid-Schiff staining indicated that mucus gland secretion was also induced by norepinephrine.
Copyright © 2011 Elsevier Ltd. All rights reserved.
The basic helix-loop-helix transcription factor Neurog3 (Neurogenin3 or Ngn3) actively drives endodermal progenitor cells towards endocrine islet cell differentiation during embryogenesis. Here, we manipulate Neurog3 expression levels in endocrine progenitor cells without altering its expression pattern using heterozygosity and a hypomorph. Lowered Neurog3 gene dosage in the developing pancreatic epithelium reduces the overall production of endocrine islet cells without significantly affecting the proportions of various islet cell types that do form. A reduced Neurog3 production level in the endocrine-directed pancreatic progenitor population activates the expression of Neurog3 in an increased number of epithelial progenitors. Yet a significant number of these Neurog3+ cells detected in heterozygous and hypomorphic pancreata, possibly those that express low levels of Neurog3, move on to adopt pancreatic ductal or acinar fates. These data directly demonstrate that achieving high levels of Neurog3 expression is a critical step for endocrine commitment from multipotent pancreatic progenitors. These findings also suggest that a high level of Neurog3 expression could mediate lateral inhibition or other unknown feedback mechanisms to regulate the number of cells that initiate Neurog3 transcription and protein production. The control of Neurog3+ cell number and the Neurog3 threshold-dependent endocrine differentiation mechanism combine to select a specific proportion of pancreatic progenitor cells to adopt the islet cell fate.
Copyright 2009 Elsevier Inc. All rights reserved.
Neutrophils may play important roles in chronic airway diseases. Pseudomonas is a common pathogen in some chronic airway diseases, and expression of the neutrophil chemoattractant interleukin-8 (IL-8) is induced by Pseudomonas in various cells in vitro. Here we examine the localization of IL-8 mRNA expression after incubating human and dog bronchi with Pseudomonas supernatant in vitro. To examine IL-8 expression in recruited neutrophils, we also superfused the dog bypassed tracheal segment with Pseudomonas supernatant in vivo and measured neutrophil number and IL-8 concentration in luminal fluid; simultaneously, we introduced Pseudomonas supernatant by catheter in a peripheral airway. After 6 h, we analyzed IL-8 mRNA expression and localization in removed tissue. Unincubated bronchi showed no IL-8 mRNA expression, but incubation with Pseudomonas supernatant in vitro resulted in IL-8 mRNA expression in surface epithelial, gland duct, and a subpopulation of serous gland cells. In vivo, introduction of Pseudomonas supernatant into dog trachea and peripheral airways caused IL-8 mRNA expression in epithelial and gland duct cells but also in the recruited neutrophils. Pseudomonas lipopolysaccharide alone was without effect in vitro and in vivo. We conclude that Pseudomonas products, but not lipopolysaccharide, stimulate IL-8 expression in airways and that this expression occurs primarily in surface epithelial and gland duct cells, thus bringing the chemoattractant to the bacterial site. Furthermore, IL-8 expression in recruited neutrophils provides a potential mechanism for positive feedback of this protective antibacterial response.