Moving patronin foci and growing microtubule plus ends direct the spatiotemporal dynamics of Rho signaling and myosin during apical constriction

The contraction of the amnioserosa by apical constriction provides the major force for Drosophila dorsal closure. The nucleation, movement and dispersal of apicomedial actomyosin complexes generate pulsed constrictions during early dorsal closure whereas persistent apicomedial and circumapical actomyosin complexes drive the unpulsed constrictions that follow. What governs the spatiotemporal assembly of these distinct complexes, endows them with their pulsatile dynamics, and directs their motility remains unresolved. Here we identify an essential role for microtubule growth in regulating the timely contraction of the amnioserosa. We show that a symmetric cage of apical microtubules forms around the coalescing apicomedial myosin complex. An asymmetric tail of microtubules then trails the moving myosin complex and disperses as the myosin complex dissolves. Perturbing microtubule growth reduced the coalescence and movement of apicomedial myosin complexes and redistributed myosin and its activator, Rho kinase to the circumapical pool and altered the cell constriction and tissue contraction dynamics of the amnioserosa. We show that RhoGEF2, the activator of the Rho1 GTPase, is transiently associated with microtubule plus end binding protein EB1 and the apicomedial actomyosin complex. Our results suggest that microtubule growth from moving patronin platforms modulates actomyosin contractility through the spatiotemporal regulation of Rho1 activity. We propose that microtubule reorganisation enables a self-organising, mechanosensitive feedback loop that buffers the tissue against mechanical stresses by modulating actomyosin contractility.

A myofibre model for the study of uterine excitation-contraction dynamics

As the uterus remodels in preparation for delivery, the excitability and contractility of the uterine smooth muscle layer, the myometrium, increase drastically. But when remodelling proceeds abnormally it can contribute to preterm birth, slow progress of labour, and failure to initiate labour. Remodelling increases intercellular coupling and cellular excitability, which are the main targets of pharmaceutical treatments for uterine contraction disorders. However, the way in which electrical propagation and force development depend on intercellular coupling and cellular excitability is not fully understood. Using a computational myofibre model we study the dependency of electrical propagation and force development on intercellular coupling and cellular excitability. This model reveals that intercellular coupling determines the conduction velocity. Moreover, our model shows that intercellular coupling alone does not regulate force development. Further, cellular excitability controls whether conduction across the cells is blocked. Lastly, our model describes how cellular excitability regulates force development. Our results bridge cellular factors, targeted by drugs to regulate uterine contractions, and tissue level electromechanical properties, which are responsible for delivery. They are a step forward towards understanding uterine excitation-contraction dynamics and developing safer and more efficient pharmaceutical treatments for uterine contraction disorders.

Monitoring and modelling drainage network dynamics of a Mediterranean catchment

<p>Empirical evidence indicates that the active part of the drainage networks, i.e. that characterized by flowing water, is not static but, conversely, it experiences significant expansion/contraction dynamics produced by the interactions between hydrological and climatic variability, morphological features and soil properties in the contributing catchment. The expansion and contraction dynamics of the "wet" component of the river network can be identified in a wide range of climatic conditions, particularly in the headwaters. In these areas, the observed river network dynamics largely depend on the capacity of the upstream drainage area to concentrate surface runoff in channelized sites.</p><p>The study presents a research activity carried out in the framework of the European project "DyNET: Dynamical River Networks" (http://www.erc-dynet.it/), specifically aimed at analysing in detail the processes and agents overseeing changes in form and in the length of river networks in a Mediterranean environment. The contribution describes the first results achieved in the southernmost of the basins under investigation in the DyNET project, namely the Turbolo creek catchment (Calabria, Southern Italy). Bi-weekly surveys were conducted in two sub-catchments having a total area of more than 1 km<sup>2</sup>, both during the recession (contraction) and reactivation (expansion) phases of the drainage network. The empirical data were used for the validation of a statistical model of the wet network dynamics, designed to estimate the total length of the active network over time. This length was distributed spatially on the river network in an objective way by defining a two-way relationship between active stream length and the Topographic Wetness Index (TWI). The modelling of the network contraction and expansion dynamics was possible using a few meteorological and hydrological variables. The combined use of information on the overall length of the network and the TWI led to a reasonably good representation of the drainage network dynamics over space and time.</p>

UAV thermal images to support the study of the expansion and contraction dynamics of river networks: a preliminary methodological approach

<p>River networks are dynamic entities, periodically subject to expansion and contraction processes due to natural hydrological and climatic fluctuations. The ERC project "DyNET: Dynamical River Networks" aims at providing a systematic and quantitative description of such processes. The experimental activities are focused on the mapping at the basin scale of the active (i.e., characterized by flowing water) portion of the river network with the aid of drones, satellite images and field surveys, for the collection of data useful to the modelling of evolutionary processes and the development of theories to be extended on a regional scale. The use of UAVs (Unmanned Air Vehicles) specifically concerns the observation of the space-time evolution of processes, allowing to monitor wide areas and identify the presence/absence of flowing water in the river network with the help of infrared (IR) thermal imaging cameras.</p><p>The contribution discusses the effectiveness of UAVs for river networks dynamics monitoring in the Turbolo creek network (Calabria, southern Italy). Specifically, an experimental method is described that identifies and extrapolates from thermal images the pixels representing the active river network. The method is defined based on multiple acquisitions of thermal IR images on some channelized sites in different periods of the year, weather conditions, daytimes and flight altitudes. Several surveys were carried out in autumn, winter and spring seasons, with variable cloud conditions, always repeating the same flight plan, at three different altitudes and at three different times for each day of analysis. During the experiments, air temperature data were recorded by a weather station near the test area, as well as the water temperature values ​​in a small control area in the river bed, with the ascertained presence of water, monitored by the UAV. The thermal images were analyzed on GIS software, extrapolating the pixels falling within a range of values defined from the control area. The "water pixels" thus obtained allowed, through appropriate post-processing, to reconstruct the active river network even in areas not accessible by land. The methodology developed allows defining, for different periods of the year and weather conditions, optimal altitudes and flight times to accurately identify the expansion/contraction dynamics of river networks.</p>