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The lymphatic system consists of a vessel network lined by specialized lymphatic endothelial cells (LECs) that are responsible for tissue fluid homeostasis and immune cell trafficking. The mechanisms for organ-specific LEC responses to environmental cues are not well understood. We found robust lymphangiogenesis during influenza A virus infection in the adult mouse lung. We show that the number of LECs increases twofold at 7 days post-influenza infection (dpi) and threefold at 21 dpi, and that lymphangiogenesis is preceded by lymphatic dilation. We also show that the expanded lymphatic network enhances fluid drainage to mediastinal lymph nodes. Using EdU labeling, we found that a significantly higher number of pulmonary LECs are proliferating at 7 dpi compared to LECs in homeostatic conditions. Lineage tracing during influenza indicates that new pulmonary LECs are derived from preexisting LECs rather than non-LEC progenitors. Lastly, using a conditional LEC-specific YAP/TAZ knockout model, we established that lymphangiogenesis, fluid transport and the immune response to influenza are independent of YAP/TAZ activity in LECs. These findings were unexpected, as they indicate that YAP/TAZ signaling is not crucial for these processes. [ABSTRACT FROM AUTHOR]

Synaptic plasticity is an underlying mechanism of learning and memory in neural systems, but it is controversial whether synaptic efficacy is modulated in a graded or binary manner. It has been argued that binary synaptic weights would be less susceptible to noise than graded weights, which has impelled some theoretical neuroscientists to shift from the use of graded to binary weights in their models. We compare retrieval performance of models using both binary and graded weight representations through numerical simulations of stochastic attractor networks. We also investigate stochastic attractor models using multiple discrete levels of weight states, and then investigate the optimal threshold for dilution of binary weight representations. Our results show that a binary weight representation is not less susceptible to noise than a graded weight representation in stochastic attractor models, and we find that the load capacities with an increasing number of weight states rapidly reach the load capacity with graded weights. The optimal threshold for dilution of binary weight representations under stochastic conditions occurs when approximately 50% of the smallest weights are set to zero. [ABSTRACT FROM AUTHOR]

The lung is a relatively quiescent tissue comprised of infrequently proliferating epithelial, endothelial, and interstitial cell populations. No classical stem cell hierarchy has yet been described for the maintenance of this essential tissue; however, after injury, a number of lung cell types are able to proliferate and reconstitute the lung epithelium. Differentiated mature epithelial cells and newly recognized local epithelial progenitors residing in specialized niches may participate in this repair process. This review summarizes recent discoveries and controversies, in the field of stem cell biology, that are not only challenging, but also advancing an understanding of lung injury and repair. Evidence supporting a role for the numerous cell types believed to contribute to lung epithelial homeostasis is reviewed, and initial studies employing cell-based therapies for lung disease are presented. As a detailed understanding of stem cell biology, lung development, lineage commitment, and epithelial differentiation emerges, an ability to modulate lung injury and repair is likely to follow. [ABSTRACT FROM AUTHOR]

Constitutively expressed Fas ligand (FasL) in several distinct epithelial cell types appears to protect tissues by inducing apoptosis of Fas+ immune cells during inflammatory reactions. To study the relationship of Fasl. and inflammation process in cornea, we examined the effects of inflammatory cytokine IL-1β on the FasL production, expression and cytotoxic function in corneal endothelial cells. In this paper, we demonstrate that IL-1β inhibits the FasL production and expression in corneal endothelial cells. The promoter activities of FasL in these cells are reduced by IL-1β in a dose-dependent manner. Finally, we also find that IL-1β block the cytotoxic effects of FasL derived from corneal endothelial cells to the Fas+ target cells. These data support the view that FasL derived from corneal endothelial cells modulate inflammation within cornea. [ABSTRACT FROM AUTHOR]

Apoptotic cells in tissue sections can be localized by in situ labelling of partly degraded DNA. In a heterogeneous population of cells, however, the specific identity of cell types undergoing apoptosis often cannot be reliably achieved at the light microscope level because of the marked alterations in cellular morphology that characterize apoptosis. In order to clearly specify cell types undergoing apoptosis, in situ end labelling has been coupled to immunohistochemistry. This method is limited by the availability of antibodies that bind to cell-specific protein markers in tissue sections. In contrast, we describe a method that combines in situ end labelling with in situ hybridization, a technique that specifies cell types based on mRNA expression. Taking advantage of the specific expression of surfactant protein C mRNA in type II alveolar epithelial cells, we demonstrate that this technique has the ability to localize alveolar type II cells undergoing apoptosis in vivo after the intratracheal instillation of an antibody that activates the cell surface Fas protein. The wide availability of cell-specific gene markers suggests that this method can be adapted to define cell types that undergo apoptosis during various physiological and pathological states in vivo. [ABSTRACT FROM AUTHOR]

The somatosensory (SI) cortex of mice displays a patterned, nonuniform distribution of neurons in layer IV called the 'barrelfield' (ref. 1). Thalamocortical afferents (TCAs) that terminate in layer IV are segregated such that each barrel, a readily visible cylindrical array of neurons surrounding a cell-sparse center, represents a distinct receptive field. TCA arbors are confined to the barrel hollow and synapse on barrel-wall neurons whose dendrites are oriented toward the center of the barrel. Mice homozygous for the barrelless (brl) mutation, which occurred spontaneously in ICR stock at Université de Lausanne (Switzerland), fail to develop this patterned distribution of neurons, but still display normal topological organization of the SI cortex. Despite the absence of barrels and the overlapping zones of TCA arborization, the size of individual whisker representations, as judged by 2-deoxyglucose uptake, is similar to that of wild-type mice. We identified adenylyl cyclase type I (Adcy1) as the gene disrupted in brl mutant mice by fine mapping of proximal chromosome 11, enzyme assay, mutation analysis and examination of mice homozygous for a targeted disruption of Adcy1. These results provide the first evidence for involvement of cAMP signalling pathways in pattern formation of the brain. [ABSTRACT FROM AUTHOR]

Calmodulin-based genetically encoded fluorescent calcium indicators (GCaMP-s) are powerful tools of imaging calcium dynamics from cells to freely moving animals. High affinity indicators with slow kinetics however distort the temporal profile of calcium transients. Here we report the development of reduced affinity ultrafast variants of GCaMP6s and GCaMP6f. We hypothesized that GCaMP-s have a common kinetic mechanism with a rate-limiting process in the interaction of the RS20 peptide and calcium-calmodulin. Therefore we targeted specific residues in the binding interface by rational design generating improved indicators with GCaMP6fu displaying fluorescence rise and decay times (t1/2) of 1 and 3 ms (37 °C) in vitro, 9 and 22-fold faster than GCaMP6f respectively. In HEK293T cells, GCaMP6fu revealed a 4-fold faster decay of ATP-evoked intracellular calcium transients than GCaMP6f. Stimulation of hippocampal CA1 pyramidal neurons with five action potentials fired at 100 Hz resulted in a single dendritic calcium transient with a 2-fold faster rise and 7-fold faster decay time (t1/2 of 40 ms) than GCaMP6f, indicating that tracking high frequency action potentials may be limited by calcium dynamics. We propose that the design strategy used for generating GCaMP6fu is applicable for the acceleration of the response kinetics of GCaMP-type calcium indicators. [ABSTRACT FROM AUTHOR]