Yap/Taz-TEAD activity links mechanical cues to progenitor cell behavior during zebrafish hindbrain segmentation.

Cells perceive their microenvironment through chemical and physical cues. However, how the mechanical signals are interpreted during embryonic tissue deformation to result in specific cell behaviors is largely unknown. The Yap/Taz family of transcriptional co-activators has emerged as an important regulator of tissue growth and regeneration, responding to physical cues from the extracellular matrix, and to cell shape and actomyosin cytoskeletal changes. In this study, we demonstrate the role of Yap/Taz-TEAD activity as a sensor of mechanical signals in the regulation of the progenitor behavior of boundary cells during zebrafish hindbrain compartmentalization. Monitoring of in vivo Yap/Taz activity during hindbrain segmentation indicated that boundary cells responded to mechanical cues in a cell-autonomous manner through Yap/Taz-TEAD activity. Cell-lineage analysis revealed that Yap/Taz-TEAD boundary cells decreased their proliferative activity when Yap/Taz-TEAD activity ceased, which preceded changes in their cell fate from proliferating progenitors to differentiated neurons. Functional experiments demonstrated the pivotal role of Yap/Taz-TEAD signaling in maintaining progenitor features in the hindbrain boundary cell population.

Cell segregation in the vertebrate hindbrain relies on actomyosin cables located at the interhombomeric boundaries.

Segregating cells into compartments during embryonic development is essential for growth and pattern formation. Physical mechanisms shaping compartment boundaries were recently explored in Drosophila, where actomyosin-based barriers were revealed to be important for keeping cells apart. In vertebrates, interhombomeric boundaries are straight interfaces, which often serve as signaling centers that pattern the surrounding tissue. Here, we demonstrate that in the hindbrain of zebrafish embryos cell sorting sharpens the molecular boundaries and, once borders are straight, actomyosin barriers are key to keeping rhombomeric cells segregated. Actomyosin cytoskeletal components are enriched at interhombomeric boundaries, forming cable-like structures in the apical side of the neuroepithelial cells by the time morphological boundaries are visible. When myosin II function is inhibited, cable structures do not form, leading to rhombomeric cell mixing. Downregulation of EphA4a compromises actomyosin cables and cells with different rhombomeric identity intermingle, and the phenotype is rescued enhancing myosin II activity. Moreover, enrichment of actomyosin structures is obtained when EphA4 is ectopically expressed in even-numbered rhombomeres. These findings suggest that mechanical barriers act downstream of EphA/ephrin signaling to segregate cells from different rhombomeres.

ZeGlobalTox: An Innovative Approach to Address Organ Drug Toxicity Using Zebrafish.

Toxicity is one of the major attrition causes during the drug development process. In that line, cardio-, neuro-, and hepatotoxicities are among the main reasons behind the retirement of drugs in clinical phases and post market withdrawal. Zebrafish exploitation in high-throughput drug screening is becoming an important tool to assess the toxicity and efficacy of novel drugs. This animal model has, from early developmental stages, fully functional organs from a physiological point of view. Thus, drug-induced organ-toxicity can be detected in larval stages, allowing a high predictive power on possible human drug-induced liabilities. Hence, zebrafish can bridge the gap between preclinical in vitro safety assays and rodent models in a fast and cost-effective manner. ZeGlobalTox is an innovative assay that sequentially integrates in vivo cardio-, neuro-, and hepatotoxicity assessment in the same animal, thus impacting strongly in the 3Rs principles. It Reduces, by up to a third, the number of animals required to assess toxicity in those organs. It Refines the drug toxicity evaluation through novel physiological parameters. Finally, it might allow the Replacement of classical species, such as rodents and larger mammals, thanks to its high predictivity (Specificity: 89%, Sensitivity: 68% and Accuracy: 78%).

"Safe" Chitosan/Zinc Oxide Nanocomposite Has Minimal Organ-Specific Toxicity in Early Stages of Zebrafish Development.

Marine biofouling is considered to be one of the most challenging issues affecting maritime industries worldwide. In this regard, traditional biocides, being used to combat biofouling, have high toxicity toward aquatic systems. Recently, a new chitosan/zinc oxide nanoparticle (CZNC) composite has been used as a promising "green" biocide. It is thought that because of the ecofriendly nature of chitosan, CZNCs may pave the way to developing less toxic surfaces for combating marine fouling. Zebrafish has become one of the most employed models for ecotoxicology studies. Therefore, this study aims to comprehensively evaluate any potential acute, cardio, neuro, or hepatotoxic effect of CZNCs using zebrafish embryos. As evidenced by the acute toxicity assays, exposing zebrafish embryos to CZNCs (25-200 mg/L) did not elicit any signs of acute toxicity or mortality, suggesting a hypothetical LC50 higher than the maximum dose employed. CZNCs, at a concentration of 250 mg/L, also showed no cardiotoxic or neurotoxic effects. At the same dosage, a minor hepatotoxic effect was observed in zebrafish embryos exposed to CZNCs. However, the observed hepatotoxicity had no effect on embryo survival even after long-term (10-days) exposure to CZNCs. We believe our results add valuable information to the potential toxicity of chitosan/metal oxide nanocomposites, which may provide new insights into the synthesis of ecofriendly coatings with improved antifouling performance and a low adverse impact on the marine environment.