Fin ray branching is defined by TRAP+ osteolytic tubules in zebrafish.

The shaping of bone structures relies on various cell types and signaling pathways. Here, we use the zebrafish bifurcating fin rays during regeneration to investigate bone patterning. We found that the regenerating fin rays form via two mineralization fronts that undergo an osteoblast-dependent fusion/stitching until the branchpoint, and that bifurcation is not simply the splitting of one unit into two. We identified tartrate-resistant acid phosphatase-positive osteolytic tubular structures at the branchpoints, hereafter named osteolytic tubules (OLTs). Chemical inhibition of their bone-resorbing activity strongly impairs ray bifurcation, indicating that OLTs counteract the stitching process. Furthermore, by testing different osteoactive compounds, we show that the position of the branchpoint depends on the balance between bone mineralization and resorption activities. Overall, these findings provide a unique perspective on fin ray formation and bifurcation, and reveal a key role for OLTs in defining the proximo-distal position of the branchpoint.

Yap induces osteoblast differentiation by modulating Bmp signalling during zebrafish caudal fin regeneration.

Osteoblast differentiation is a key process for bone homeostasis and repair. Multiple signalling pathways have been associated with osteoblast differentiation, yet much remains unknown on how this process is regulated in vivo Previous studies have proposed that the Hippo pathway transcriptional co-activators YAP and TAZ (also known as YAP1 and WWTR1, respectively) maintain progenitor stemness and inhibit terminal differentiation of osteoblasts, whereas others suggest they potentiate osteoblast differentiation and bone formation. Here, we use zebrafish caudal fin regeneration as a model to clarify how the Hippo pathway regulates de novo bone formation and osteoblast differentiation. We demonstrate that Yap inhibition leads to accumulation of osteoprogenitors and prevents osteoblast differentiation in a cell non-autonomous manner. This effect correlates with a severe impairment of Bmp signalling in osteoblasts, likely by suppressing the expression of the ligand bmp2a in the surrounding mesenchymal cells. Overall, our findings provide a new mechanism of bone formation through the Hippo-Yap pathway, integrating Yap in the signalling cascade that governs osteoprogenitor maintenance and subsequent differentiation during zebrafish caudal fin regeneration.

Radiological Scouting, Monitoring and Inspection Using Drones.

Human populations and natural ecosystems are bound to be exposed to ionizing radiation from the deposition of artificial radionuclides resulting from nuclear accidents, nuclear devices or radiological dispersive devices ("dirty bombs"). On the other hand, Naturally Occurring Radioactive Material industries such as phosphate production or uranium mining, contribute to the on site storage of residuals with enhanced concentrations of natural radionuclides. Therefore, in the context of the European agreements concerning nuclear energy, namely the European Atomic Energy Community Treaty, monitoring is an essential feature of the environmental radiological surveillance. In this work, we obtain 3D maps from outdoor scenarios, and complete such maps with measured radiation levels and with its radionuclide signature. In such scenarios, we face challenges such as unknown and rough terrain, limited number of sampled locations and the need for different sensors and therefore different tasks. We propose a radiological solution for scouting, monitoring and inspecting an area of interest, using a fleet of drones and a controlling ground station. First, we scout an area with a Light Detection and Ranging sensor onboard a drone to accurately 3D-map the area. Then, we monitor that area with a Geiger-Müller Counter at a low-vertical distance from the ground to produce a radiological (heat)map that is overlaid on the 3D map of the scenario. Next, we identify the hotspots of radiation, and inspect them in detail using a drone by landing on them, to reveal its radionuclide signature using a Cadmium-Zinc-Telluride detector. We present the algorithms used to implement such tasks both at the ground station and on the drones. The three mission phases were validated using actual experiments in three different outdoor scenarios. We conclude that drones can not only perform the mission efficiently, but in general they are faster and as reliable as personnel on the ground.

Performance Analysis of Geiger-Müller and Cadmium Zinc Telluride Sensors Envisaging Airborne Radiological Monitoring in NORM Sites.

Radiological monitoring is fundamental for compliance with radiological protection policies in the aftermath of radiological events, such as nuclear accidents, terrorism, and out-of-commission uranium mines. An effective strategy for radiation monitoring is to use radiation detectors coupled with Unmanned Aerial Vehicles (UAVs), enabling for quicker surveillance of large areas without involving the need of human presence in the target area. The main aim of this study was to formulate the parameters for a UAV flight strategy in preparation for future field measurements using Geiger-Muller Counters (GMC) and Cadmium Zinc Telluride (CZT) spectrometers. As a proof of concept, the prepared flight strategy will be used to survey out-of-commission uranium mines in northern Portugal. Procedures to assure the calibration of the CZT and verification of the GMCs were conducted, as well as a sensitivity analysis of the sensors considering different acquisition times, distance to source, and detector response time. This article reports specific parameters, such as UAV distance to ground, time of exposition, speed, and the methodology to perform the identification and calculate the activity of possible radioactive sources. An effective flight strategy is also presented, aiming to use radiation detectors coupled with UAVs to undertake extensive monitoring of areas with enhanced levels of environmental radiation, which is of prime importance due to the lasting hazardous effects of enhanced environmental radiation in the nearby ecosystem and population.

Targeted radionuclide therapy directed to the tumor phenotypes: A dosimetric approach using MC simulations.

BACKGROUND: In Targeted Radionuclide Therapy (TRT), the continuous technological effort in imaging tumor phenotypes (i.e. sub-volumes with different phenotypic characteristics) and in precise radiopharmaceutical tumor-targeting, is allowing for a better dosimetric optimization at the tumor phenotype level. The aim of this study was to evaluate the dosimetric efficiency (considering strategic absorbed dose delivery to the phenotypes) of personalized TRT directed to the tumor phenotypes. METHODS: The dosimetric assessment was performed using a four-phenotype realistic tumor model implemented within the ICRP reference voxel phantom and simulations using the state-of-the-art Monte Carlo program PENELOPE. The dose assessment was performed for five radionuclides commonly used in therapy and/or diagnostic procedures: 125I, 99mTc, 177Lu, 161Tb and 67Ga. Two irradiation scenarios were considered: (i) the Whole Tumor Treatment Planning Scenario (WTTPS), i.e. the four phenotypes irradiated with the same radionuclide; (ii) the Phenotype Treatment Planning Scenario (PTPS), i.e. each phenotype irradiated by a single radionuclide. The optimal radionuclide configurations were studied considering the maximization of the absorbed dose delivered to the tumor and the minimization of dose to healthy tissues. RESULTS: In WTTPS, 125I outperforms the other radionuclides in terms of the ratio of the maximum absorbed dose delivered to the tumor and the minimum absorbed dose delivered to healthy tissues. In the PTPS, the use of 161Tb in combination with the other radionuclides maximizes the absorbed dose in the tumor tissues while simultaneously minimizing dose to healthy tissue, compared to the WTTPS. In agreement with recent pre-clinical studies, our computational results confirm and indicate the beneficial additive dosimetric effects of Auger and conversion electrons of 161Tb with respect to 177Lu, when considering the same cumulated activity for both. Interestingly, in considering a realistic tumor model, the better dosimetric performances of 161Tb were confirmed also for tumor volumes ranging from 1.98 cm3 to 33.32 cm3. CONCLUSIONS: Dose assessment in realistic non-homogeneous tumor models could provide more insights with respect to consider only homogenous water-spheres tumor models and should be taken into account in dosimetry-based TRT planning studies.

A regeneration-triggered metabolic adaptation is necessary for cell identity transitions and cell cycle re-entry to support blastema formation and bone regeneration.

Regeneration depends on the ability of mature cells at the injury site to respond to injury, generating tissue-specific progenitors that incorporate the blastema and proliferate to reconstitute the original organ architecture. The metabolic microenvironment has been tightly connected to cell function and identity during development and tumorigenesis. Yet, the link between metabolism and cell identity at the mechanistic level in a regenerative context remains unclear. The adult zebrafish caudal fin, and bone cells specifically, have been crucial for the understanding of mature cell contribution to tissue regeneration. Here, we use this model to explore the relevance of glucose metabolism for the cell fate transitions preceding new osteoblast formation and blastema assembly. We show that injury triggers a modulation in the metabolic profile at early stages of regeneration to enhance glycolysis at the expense of mitochondrial oxidation. This metabolic adaptation mediates transcriptional changes that make mature osteoblast amenable to be reprogramed into pre-osteoblasts and induces cell cycle re-entry and progression. Manipulation of the metabolic profile led to severe reduction of the pre-osteoblast pool, diminishing their capacity to generate new osteoblasts, and to a complete abrogation of blastema formation. Overall, our data indicate that metabolic alterations have a powerful instructive role in regulating genetic programs that dictate fate decisions and stimulate proliferation, thereby providing a deeper understanding on the mechanisms regulating blastema formation and bone regeneration.

Yap Regulates Müller Glia Reprogramming in Damaged Zebrafish Retinas.

Vertebrates such as zebrafish have the outstanding ability to fully regenerate their retina upon injury, while mammals, including humans, do not. In zebrafish, upon light-induced injury, photoreceptor regeneration is achieved through reprogramming of Müller glia cells, which proliferate and give rise to a self-renewing population of progenitors that migrate to the lesion site to differentiate into the new photoreceptors. The Hippo pathway effector YAP was recently implicated in the response to damage in the retina, but how this transcription coactivator is integrated into the signaling network regulating Müller glia reprogramming has not yet been explored. Here, we show that Yap is required in Müller glia to engage their response to a lesion by regulating their cell cycle reentry and progenitor cell formation, contributing to the differentiation of new photoreceptors. We propose that this regulation is accomplished through a lin28a-ascl1a-dependent mechanism, bona fide Müller glia-reprogramming factors. Overall, this study presents Yap as a key regulator of zebrafish Müller glia reprogramming and consequently retina regeneration upon injury.

Monte Carlo calculation of quality correction factors based on air kerma and absorbed dose to water in medium energy x-ray beams.

Clinical dosimetry is typically performed using ion chambers calibrated in terms of absorbed dose to water. As primary measurement standards for this quantity for low and medium energy x-rays are available only since a few years, most dosimetry protocols for this photon energy range are still based on air kerma calibration. For that reason, data for beam quality correction factors [Formula: see text], necessary for the application of dose to water based protocols, are scarce in literature. Currently the international IAEA TRS-398 Code of Practice is under revision and new [Formula: see text] factors for a large number of ion chambers will be introduced in the update of this protocol. Several international groups provided the IAEA with experimental and Monte Carlo based data for this revision. Within the European Community the EURAMET 16NRM03 RTNORM project was initiated for that purpose. In the present study, Monte Carlo based results for the beam quality correction factors in medium energy x-ray beams for six ion chambers applying different Monte Carlo codes are presented. Additionally, the perturbation factor p Q , necessary for the calculation of dose to water from an air kerma calibration coefficient, was determined. The beam quality correction factor [Formula: see text] for the chambers varied in the investigated energy range by about 4%-5%, and for five out of six chambers the data could be fitted by a simple logarithmic function, if the half-value-layer was used as the beam quality specifier. Corresponding data using different Monte Carlo codes for the same ion chamber agreed within 0.5%. For the perturbation factor p Q , the data did not obey a comparable simple relationship with the beam quality specifier. The variation of p Q for all ion chambers was in the range of 3%-4%. Compared to recently published data, our p Q data is around 1% larger, although the same Monte Carlo code has been used. Compared to the latest experimental data, there are even deviations in the range of 2%.