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How morphogen gradients are formed in target tissues is a key question for understanding the mechanisms of morphological patterning. Here, we review different mechanisms of morphogen gradient formation from theoretical and experimental points of view. First, a simple, comprehensive overview of the underlying biophysical principles of several mechanisms of gradient formation is provided. We then discuss the advantages and limitations of different experimental approaches to gradient formation analysis.

Positional information is essential for the cell's fate in tissue. In the wing imaginal disk of Drosophila melanogaster positional information is provided by a concentration gradient of the morphogens Decapentaplegic (Dpp) and Wingless. We use a 3D-epifluorescence setup to unravel the spatio-temporal distribution of YFP-labeled Dpp after secretion by specialized producing cells. With our approach we are able to characterize the Dpp distribution in the wing disk in all three dimensions in vivo. Most Dpp is located apically in a layer of ∼5 μm. To elucidate how the gradient is maintained individual endosomes containing Dpp are followed. We found that endosomes contain up to 100 Dpp molecules allowing us to follow endosomes for hundreds of frames with high spatio-temporal accuracy in three dimensions.The Dpp concentration in each endosome was directly determined from the fluorescence intensity. We find a constant Dpp fraction of 60% in endosomes, agreeing with the fixed fraction found in FRAP experiments. Sudden changes in Dpp content of up to 15 Dpp molecules are observed, indicating that Dpp is endocytosed in clusters into vesicles before vesicle fusion with endosomes occurs. Surprisingly multiple preferred Dpp cluster sizes are found. Measuring Dpp in- and outflow results in rates on the order of minutes. Labeling different types of endosomes allows us to calculate Dpp degradation and recycling rates.Endosome mobility plays an important role in maintaining the Dpp gradient. We find that Dpp-containing endosomes close to the Dpp source are transported during 15% of the time. Further away this percentage drops, indicating that transport via endosomes is playing a less important role in maintaining the morphogen gradient. Our study leads to a mechanistic model for gradient formation on the level of the mobility of individual Dpp endosomes and molecules.

The effects of in-vivo and in-vitro abscisic acid (ABA) treatments on the surface charge density (σ) of barley (Hordeum vulgare L.) thylakoids were compared using 9-aminoacridine fluorescence. The estimated surface charge density of isolated thylakoid membranes from control (non-treated) barley leaves was-0.065 C · m(-2). The net negative surface charge density decreased after application of various concentrations of ABA (10(-6), 10(-5) M) for 7 d in-vivo, the more pronounced effect being observed at 10(-5) M ABA. When ABA was added to the suspension of isolated thylakoids the opposite effect was observed. The average charge density increased in in-vitro-treated thylakoids at 10(-5) M ABA to -0.081 C · m(-2). The results are discussed in terms of a specific ABA-induced influence of the composition and-or stoicheometry of charged protein complexes within the thylakoid membranes.

Summary Background Cell-to-cell communication at the synapse involves synaptic transmission as well as signaling mediated by growth factors, which provide developmental and plasticity cues. There is evidence that a retrograde, presynaptic transforming growth factor-β (TGF-β) signaling event regulates synapse development and function in Drosophila . Results Here we show that a postsynaptic TGF-β signaling event occurs during larval development. The type I receptor Thick veins (Tkv) and the R-Smad transcription factor Mothers-against-dpp (Mad) are localized postsynaptically in the muscle. Furthermore, Mad phosphorylation occurs in regions facing the presynaptic active zones of neurotransmitter release within the postsynaptic subsynaptic reticulum (SSR). In order to monitor in real time the levels of TGF-β signaling in the synapse during synaptic transmission, we have established a FRAP assay to measure Mad nuclear import/export in the muscle. We show that Mad nuclear trafficking depends on stimulation of the muscle. Conclusions Our data suggest a mechanism linking synaptic transmission and postsynaptic TGF-β signaling that may coordinate nerve-muscle development and function.

Building the neural tube The development of the neural tube is regulated by a pair of morphogens acting in opposing gradients. The mature neural tube is built from a variety of different cell types organized in a consistent dorsal-ventral pattern. Zagorski et al. asked how this pattern is defined in a reproducible way from individual to individual. The morphogens define positions most accurately toward the top of their respective gradients, but things get a bit messy in the middle. Modeling the gene regulatory network's response as a maximum likelihood estimation from the combined input of both morphogens, however, succeeds at defining even the intermediate positions. Thus, the computation of position by the gene regulatory network establishes accurate tissue patterning despite messy inputs. Science , this issue p. 1379

The paper examines the impact of the economic globalization on the economic growth in Bulgaria for the period 2007-2018. The aim of the tudy is to reveal the impact of the economic globalization on the economic growth. The research of the link economic globalization and its influence on the economic growth is performed via generalized method of moments (GMM), descriptive analysis and deductive approach. The conclusion that has been reached is that economic globalization has a positive impact on the economic growth for the period 2007-2018. The main channel of influence is the international trade.

All vertebrates have a spinal cord with dimensions and shape specific to their species. Yet how species‐specific organ size and shape are achieved is a fundamental unresolved question in biology. The formation and sculpting of organs begins during embryonic development. As it develops, the spinal cord extends in anterior–posterior direction in synchrony with the overall growth of the body. The dorsoventral (DV) and apicobasal lengths of the spinal cord neuroepithelium also change, while at the same time a characteristic pattern of neural progenitor subtypes along the DV axis is established and elaborated. At the basis of these changes in tissue size and shape are biophysical determinants, such as the change in cell number, cell size and shape, and anisotropic tissue growth. These processes are controlled by global tissue‐scale regulators, such as morphogen signaling gradients as well as mechanical forces. Current challenges in the field are to uncover how these tissue‐scale regulatory mechanisms are translated to the cellular and molecular level, and how regulation of distinct cellular processes gives rise to an overall defined size. Addressing these questions will help not only to achieve a better understanding of how size is controlled, but also of how tissue size is coordinated with the specification of pattern. This article is categorized under:Establishment of Spatial and Temporal Patterns > Regulation of Size, Proportion, and TimingSignaling Pathways > Global Signaling MechanismsNervous System Development > Vertebrates: General Principles, The vertebrate spinal cord changes its shape and size during development. These changes depend on cell behaviours that are regulated by global tissue‐scale mechanisms.