The guanine exchange factor vav controls axon growth and guidance during Drosophila development

The Vav proteins are guanine exchange factors (GEFs) that trigger the activation of the Rho GTPases in general and the Rac family in particular. While the role of the mammalian vav genes has been extensively studied in the hematopoietic system and the immune response, there is little information regarding the role of vav outside of these systems. Here, we report that the single Drosophila vav homolog is ubiquitously expressed during development, although it is enriched along the embryonic ventral midline and in the larval eye discs and brain. We have analyzed the role that vav plays during development by generating Drosophila null mutant alleles. Our results indicate that vav is required during embryogenesis to prevent longitudinal axons from crossing the midline. Later on, during larval development, vav is required within the axons to regulate photoreceptor axon targeting to the optic lobe. Finally, we demonstrate that adult vav mutant escapers, which exhibit coordination problems, display axon growth defects in the ellipsoid body, a brain area associated with locomotion control. In addition, we show that vav interacts with other GEFs known to act downstream of guidance receptors. Thus, we propose that vav acts in coordination with other GEFs to regulate axon growth and guidance during development by linking guidance signals to the cytoskeleton via the modulation of Rac activity.Research in our laboratories is funded by the Spanish Ministerio de Ciencia y Tecnología (MCYT) (BFU2007-64715/BMC to M.D.M.-B., CSD-2007-00008), the European Molecular Biology Organization Young Investigator Program, and the Junta de Andalucía (CVI-280 and PO6-CVI1592). M.M. wassupported by postdoctoral fellowships from the MCYT and the Juan de la Cierva Program. The institutional support from the Junta de Andalucía to the Centro Andaluz de Biología del Desarrollo is acknowledged.Peer Reviewe

A Novel Wastewater Load Allocation Approach for River Basins Using Simulation-Optimization Models

In this study, a new wastewater load allocation approach using a linked simulation-optimization model is proposed to determine the receiving body-based discharge limits by considering the discharge standards used by the European Union Water Framework Directive. By using the proposed approach, wastewater loads of point sources can be determined in such a way that the parameters exceeding the water quality targets (WQT) in receiving water bodiesmeet the relevant WQT. The simulation part is used to determine pollutantconcentrations throughout the river system using the AQUATOX water quality simulation model. However, since AQUATOX is an independent simulation modeland its source code is not publicly available, it is not possible to execute it with the optimization model for the generated load combinations. Therefore, a concentration-response matrix (CRM) is developed as a surrogate water simulation model by using the outputsoftheAQUATOX model. After this process, the developed CRMis integrated into an optimization model where the heuristic differential evolution (DE) optimization approach is used. The performance of the proposed simulation-optimization approach is evaluated on a sub-watershed of the Kucuk Menderes River Basin by considering different wasteload allocation scenarios for the CBOD5 water quality parameter. The results showed that the proposed simulation-optimization approach can effectively allocate the wastewater loads among different point sources by considering the WQT values of the CBOD5 parameter.</jats:p

Investigating CNS synaptogenesis at single-synapse resolution by combining reverse genetics with correlative light and electron microscopy

Determining direct synaptic connections of specific neurons in the central nervous system (CNS) is a major technical challenge in neuroscience. As a corollary, molecular pathways controlling developmental synaptogenesis in vivo remain difficult to address. Here, we present genetic tools for efficient and versatile labeling of organelles, cytoskeletal components and proteins at single-neuron and single-synapse resolution in Drosophila mechanosensory (ms) neurons. We extended the imaging analysis to the ultrastructural level by developing a protocol for correlative light and 3D electron microscopy (3D CLEM). We show that in ms neurons, synaptic puncta revealed by genetically encoded markers serve as a reliable indicator of individual active zones. Block-face scanning electron microscopy analysis of ms axons revealed T-bar-shaped dense bodies and other characteristic ultrastructural features of CNS synapses. For a mechanistic analysis, we directly combined the single-neuron labeling approach with cell-specific gene disruption techniques. In proof-of-principle experiments we found evidence for a highly similar requirement for the scaffolding molecule Liprin-alpha and its interactors Lar and DSyd-1 (RhoGAP100F) in synaptic vesicle recruitment. This suggests that these important synapse regulators might serve a shared role at presynaptic sites within the CNS. In principle, our CLEM approach is broadly applicable to the developmental and ultrastructural analysis of any cell type that can be targeted with genetically encoded markers