Biology subjects

Brumfeld, V.

Publications and source records attributed to Brumfeld, V..

7 recordsLinked to original sources

bioRxiv2023

Cell-mediated cholesterol crystal processing and clearance observed by 3D cryo-imaging in human atherosclerotic plaques

Atherosclerosis is a pathology affecting the arteries, characterized by the buildup of plaques in the blood vessel walls. Atherosclerosis is the main cause of cardiovascular diseases, which constitute the leading cause of death in the world. Cholesterol crystals are the main components of the plaques, which actively participate in plaque growth and rupture and do not dissolve in aqueous environments. Employing novel cryo-scanning electron microscopy techniques, we examined human atherosclerotic plaques at high resolution, in 3D, and in close to native conditions. We show that cholesterol crystal clearance occurs in advanced human plaques through the activity of cells. We suggest that this occurs by enzymatic esterification of cholesterol to cholesteryl ester, which aggregates into intra- and extra-cellular pools. This discovery provides further understanding of the disease process in atherosclerosis, and may inspire new therapeutic approaches.

pathology↗

bioRxiv2022

The petrous bone contains high concentrations of osteocytes: one possible reason why ancient DNA is better preserved in this bone.

The characterization of ancient DNA in fossil bones is providing invaluable information on the genetics of past human and other animal populations. These studies have been aided enormously by the discovery that ancient DNA is relatively well preserved in the petrous bone compared to most other bones. The reasons for this better preservation are however not well understood. Here we examine the hypothesis that one reason for better DNA preservation in the petrous bone is that fresh petrous bone contains more DNA than other bones. We therefore determined the concentrations of osteocyte cells occluded inside lacunae within the petrous bone and compared these concentrations to other bones from the domestic pig using high resolution microCT. We show that the concentrations of osteocyte lacunae in the inner layer of the pig petrous bone adjacent to the otic chamber are about three times higher than in the temporal bone, as well as the cortical bone of the femur. The sizes and shapes of the lacuna in the inner layer of the petrous bone are similar to those in the femur. We also confirm that the petrous bone lacunae do contain osteocytes using a histological stain for DNA. We therefore conclude that one possible reason for better preservation of ancient DNA in the petrous bone is that this bone initially contains up to three times more DNA than other bones, and hence during diagenesis more DNA is likely to be preserved. We also note that the osteocytes in the inner layer of the petrous bone may have a function in hearing.

zoology↗

bioRxiv2020

The effect of soil potassium and carbohydrates on xylem conductivity and embolism in an evergreen angiosperm tree and a gymnosperm tree before and after drought

Xylem embolism is a major threat to tree function and survival under drought, in natural and agricultural settings alike, with its impact increasing in light of global climate change. Conversely, potassium (K+) has been shown to increase xylem conductivity (Ks) in trees, and carbohydrates were reported to impact leaf gas exchange. In this study we examined the effects of K+ and carbohydrates on Ks in two divergent evergreen tree species that are regularly exposed to drought: pine (Pinus brutia) and lemon (Citrus x limon). Five-year-old trees were pretreated with zero, moderate, and high K+, and with ambient or elevated CO2, to experimentally increase their xylem K+ or carbohydrates levels, respectively. Trees were then monitored for Ks and embolism (using a microCT), along with leaf gas exchange and water potential, before and after a 1.5-2.5 month drought period. Potassium fertigation had a positive effect on Ks, in both species when irrigated, which was eliminated following drought. Drought decreased Ks about 10-fold in lemon, with little effect in pine. CO2-treated trees had the same Ks as control trees before and after drought. Our results indicate a positive effect of K+ on tree hydraulics, which was more pronounced in lemon than in pine, supporting the hypothesis of interaction with the angiosperm pit membrane, and not with the gymnosperm bordered pit. Yet, the elimination of this benefit following drought, and the lack of benefit from elevated carbohydrates following a short-term CO2 treatment, question the relevance of these components to tree drought resistance mechanisms. Key massagePotassium fertigation increases hydraulic conductivity and reduces xylem embolism in the gymnosperm pine, and more so in the angiosperm lemon tree, benefits which were eliminated following drought.

plant biology↗

bioRxiv2020

Cystoliths in Ficus leaves: increasing carbon fixation in saturating light by light scattering off a mineral substrate

The manner in which leaves adapt to different light intensities is key for enabling plants to survive in diverse environments and in constantly changing conditions. Many studies have addressed this subject, but little attention has been given to the effect that mineral deposits in leaves can have on photosynthesis. Here we study 6 species of Ficus and investigate how different cystolith configurations affect photosynthesis in both non-saturating and saturating light. We quantified the effect of light scattering by cystoliths on light absorption by measuring chlorophyll fluorescence intensity using microfluorimetry. We complement this by carbon assimilation measurements to directly estimate how light scattering by cystoliths affects the overall photosynthetic process. We show that light waste is reduced when irradiance is on a cystolith compared to cystolith free tissue. Moreover, light is channeled into the center of the leaf where photosynthesis occurs more efficiently than in the outer layers. This, in turn, leads to more efficient CO2 assimilation. We conclude that cystoliths contribute to photosynthesis optimization under saturating light. Cystoliths reduce the wasted portion of absorbed light under saturating irradiance by scattering light into the light-deprived leaf center. The increased efficiency may well provide important benefits to plants that form mineral scatterers.

plant biology↗

bioRxiv2019

The nasopalatine ducts of the mouse conserve a functional role in pheromone signaling

Social communication in most mammals is mediated by chemosignals, collected by active sniffing and detected mainly by the vomeronasal organ (VNO). In reptiles, however, chemosignals are delivered to the VNO through the oral cavity via the nasopalatine ducts (NPDs) - two direct passageways connecting the nasal and the oral cavities. While the structure of the NPDs is highly conserved across terrestrial vertebrate, it is unclear whether they retain any functional role in mammalian chemosignaling. Here we assess the role of the mouse NPDs in VNO function and associated behavioral responses. By reconstructing the 3D morphological architecture of the mouse snout using micro CT, we identify a net of micro-tunnels forming a direct passageway connecting the NPDs to the nasal cavity and the vomeronasal organ. We further demonstrate that physical obstruction of the NPDs destructs VNO clearance, and reduces chemosignaling-evoked neuronal activation in the medial amygdala. Obstruction of the NPDs also impaired the innate male preference for female chemosignals as well as social approach behavior, indicating the crucial role of the murine nasopalatine ducts in pheromone sensing.

neuroscience↗

bioRxiv2017

Development of High-Order Organization of Guanine-Based Reflectors Underlies the Dual Functionality of the Zebrafish Iris

Many marine organisms have evolved a reflective iris to prevent unfocused light from reaching the retina. The fish iris has a dual function, both to camouflage the eye and serving as a light barrier. Yet, the mechanism that enables this dual functionality and the benefits of using a reflective iris have remained unclear. Using synchrotron micro-focused diffraction, cryo-SEM imaging and optical analyses on zebrafish at different stages of development, we show that the complex optical response of the iris is facilitated by the development a high-order organization of multilayered guanine-based crystal reflectors and pigments. We further demonstrate how the efficient light reflector is established during development to allow the optical functionality of the eye, already at early developmental stages. These results shed light on the evolutionary drive for developing a compact reflective iris, which is widely used by many animal species.\n\nSignificance StatementThe fish iris is an exquisite example of natures remarkable engineering where specialized cells, dubbed iridophores, produce an efficient light reflector made of guanine-based crystals. This unique structure of the fish iris serves a dual function: In addition to its role as a light barrier, the iris has a second role of camouflaging the eye by creating a silvery reflectance, which merges with the fish skin. The underlying mechanism that enables the aforementioned dual functionality of the fish iris as well as the structural morphogenesis of the guanine reflector during embryonic development, remained unclear. We show that complex optical response of the iris is facilitated by the establishment of a high-order organization of multilayered guanine-based crystal reflectors and pigments.

biophysics↗

bioRxiv2017

Isoxanthopterin: An Optically Functional Biogenic Crystal in the Eyes of Decapod Crustaceans

The eyes of some aquatic animals form images through reflective optics. Shrimp, lobsters, crayfish and prawns possess reflecting superposition compound eyes, composed of thousands of square-faceted eye-units (ommatidia). Mirrors in the upper part of the eye (the distal mirror) reflect light collected from many ommatidia onto the underlying photosensitive elements of the retina, the rhabdoms. A second reflector, the tapetum, underlying the retina, back-scatters dispersed light onto the rhabdoms. Using microCT and cryo-SEM imaging accompanied by in situ micro-X-ray diffraction and micro-Raman spectroscopy, we investigated the hierarchical organization and materials properties of the reflective systems at high resolution and under close to physiological conditions. We show that the distal mirror consists of three or four layers of sparse plate-like nano-crystals. The tapetum is a diffuse reflector composed of hollow nanoparticles constructed from concentric lamellae of crystals. Isoxanthopterin, a pteridine analog of guanine, forms both the reflectors in the distal mirror and in the tapetum. The crystal structure of isoxanthopterin was determined from crystal structure prediction calculations and verified by comparison with experimental X-ray diffraction. The extended hydrogen bonded layers of the molecules results in an extremely high calculated refractive index in the H-bonded plane, n = 1.96, which makes isoxanthopterin crystals an ideal reflecting material. The crystal structure of isoxanthopterin, together with a detailed knowledge of the reflector superstructures, provide a rationalization of the reflective optics of the crustacean eye.\n\nSignificanceAquatic animals use reflectors in their eyes either to form images or to increase photon capture. Guanine is the most widespread molecular component of these reflectors. Here we show that crystals of isoxanthopterin, a pteridine analogue of guanine, form both the image-forming distal mirror and the intensity-enhancing tapetum reflector in the compound eyes of some decapod crustaceans. The crystal structure of isoxanthopterin was determined, providing an explanation for why these crystals are so well suited for efficient reflection. Pteridines were previously known only as pigments and our discovery raises the question of which other organic molecules may be used to form crystals with superior reflective properties either in organisms or in artificial optical devices.

bioengineering↗