Changes in the distribution of intermediate filament proteins and collagen IV in fetal and adult human pancreas. I. Localization of cytokeratin polypeptides

The expression patterns of individual cytokeratin polypeptides in foetal and adult human pancreatic tissues were examined using monoclonal antibodies. We demonstrated that human pancreatic epithelia in early stages of development (14 weeks of gestation) contain cytokeratins 7, 8, 18 and 19, which are typical of simple epithelia, as well as cytokeratin 4 and 17, which are characteristic of stratified epithelia. In the pancreatic ducts, most of these cytokeratins appeared to be expressed together. Cytokeratins 1, 5, 10, 13, 16 and 20 were not detectable. In contrast, the pancreatic parenchyma was only positive for cytokeratins 8 and 18, except a transient expression of cytokeratins 7 and 19 in pancreatic islets and acinar cells during the foetal development. A focal cytokeratin 7 staining of single acinar cells was seen in newborn and in adult islets. In the stromal tissue, vascular smooth muscle cells were partly reactive with cytokeratin 8 and 18 specific antibodies. The results are discussed in the light of differentiation-dependent changes in the expression of individual cytokeratin polypeptides in developing epithelia.     

Localized iron supply triggers lateral root elongation in Arabidopsis by altering the AUX1-mediated auxin distribution

Root system architecture depends on nutrient availability, which shapes primary and lateral root development in a nutrient-specific manner. To better understand how nutrient signals are integrated into root developmental programs, we investigated the morphological response of Arabidopsis thaliana roots to iron (Fe). Relative to a homogeneous supply, localized Fe supply in horizontally separated agar plates doubled lateral root length without having a differential effect on lateral root number. In the Fe uptake-defective mutant iron-regulated transporter1 (irt1), lateral root development was severely repressed, but a requirement for IRT1 could be circumvented by Fe application to shoots, indicating that symplastic Fe triggered the local elongation of lateral roots. The Fe-stimulated emergence of lateral root primordia and root cell elongation depended on the rootward auxin stream and was accompanied by a higher activity of the auxin reporter DR5-β-glucuronidase in lateral root apices. A crucial role of the auxin transporter AUXIN RESISTANT1 (AUX1) in Fe-triggered lateral root elongation was indicated by Fe-responsive AUX1 promoter activities in lateral root apices and by the failure of the aux1-T mutant to elongate lateral roots into Fe-enriched agar patches. We conclude that a local symplastic Fe gradient in lateral roots upregulates AUX1 to accumulate auxin in lateral root apices as a prerequisite for lateral root elongation.     

Herbivore and pathogen effects on tree growth are additive,but mediated by tree diversity and plant traits

Herbivores and fungal pathogens are key drivers of plant community composition and functioning. The effects of herbivores and pathogens are mediated by the diversity and functional characteristics of their host plants. However, the combined effects of herbivory and pathogen damage, and their consequences for plant performance, have not yet been addressed in the context of biodiversity–ecosystem functioning research. We analyzed the relationships between herbivory, fungal pathogen damage and their effects on tree growth in a large‐scale forest‐biodiversity experiment. Moreover, we tested whether variation in leaf trait and climatic niche characteristics among tree species influenced these relationships. We found significant positive effects of herbivory on pathogen damage, and vice versa. These effects were attenuated by tree species richness—because herbivory increased and pathogen damage decreased with increasing richness—and were most pronounced for species with soft leaves and narrow climatic niches. However, herbivory and pathogens had contrasting, independent effects on tree growth, with pathogens decreasing and herbivory increasing growth. The positive herbivory effects indicate that trees might be able to (over‐)compensate for local damage at the level of the whole tree. Nevertheless, we found a dependence of these effects on richness, leaf traits and climatic niche characteristics of the tree species. This could mean that the ability for compensation is influenced by both biodiversity loss and tree species identity—including effects of larger‐scale climatic adaptations that have been rarely considered in this context. Our results suggest that herbivory and pathogens have additive but contrasting effects on tree growth. Considering effects of both herbivory and pathogens may thus help to better understand the net effects of damage on tree performance in communities differing in diversity. Moreover, our study shows how species richness and species characteristics (leaf traits and climatic niches) can modify tree growth responses to leaf damage under real‐world conditions.     

G Protein-coupled Receptor (GPCR) Signaling via Heterotrimeric G Proteins from Endosomes

Some G protein-coupled receptors (GPCRs), in addition to activating heterotrimeric G proteins in the plasma membrane, appear to elicit a “second wave” of G protein activation after ligand-induced internalization. We briefly summarize evidence supporting this view and then discuss what is presently known about the functional significance of GPCR-G protein activation in endosomes. Endosomal activation can shape the cellular response temporally by prolonging its overall duration, and may shape the response spatially by moving the location of intracellular second messenger production relative to effectors.     

Carrier-free 8-azidoadenosine 5'-[gamma-32P]triphosphate

We found 8-azidoadenosine 5'-diphosphate to be a phosphoryl acceptor in the enzymatic conversion of 1,3-diphosphoglyceric acid to 3-phosphoglycerate. This has allowed us to synthesize in a single-step procedure carrier-free 8-azidoadenosine 5'-[gamma-32P]triphosphate, requiring no further purification of the end product. The synthesized 8-azidoadenosine 5'-[gamma-32P]triphosphate has been characterized and shown to meet all the criteria for a specific photoreactive ATP analogue.     

Zum histochemischen Phosphorylasenachweis im Herzinfarkt

Summary The demonstration of glycogen by PAS-method and the reaction of phosphorylase by Takeuchi et al. were performed in the hearts of rats 30 min after experimental coronary occlusion. While the cardiac muscle cells in the center of the ischemic region still contained glycogen, the cells in the border zone of the infarction did not. The phosphorylase activity was demonstrable only in those cardiac muscle cells which contained glycogen. As well known that the demonstration of phosphorylase activity is possible only if glycogen as starter is present, it is concluded that the lack of phosphorylase activity by the histochemical reaction in cells which do not contain glycogen doesn't prove the absence of the enzyme.

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Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.

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Stipendiat der Alexander von Humboldt-Stiftung.