Modeling the Glomerular Filtration Barrier and Intercellular Crosstalk

The glomerulus is a compact cluster of capillaries responsible for blood filtration and initiating urine production in the renal nephrons. A trilaminar structure in the capillary wall forms the glomerular filtration barrier (GFB), composed of glycocalyx-enriched and fenestrated endothelial cells adhering to the glomerular basement membrane and specialized visceral epithelial cells, podocytes, forming the outermost layer with a molecular slit diaphragm between their interdigitating foot processes. The unique dynamic and selective nature of blood filtration to produce urine requires the functionality of each of the GFB components, and hence, mimicking the glomerular filter in vitro has been challenging, though critical for various research applications and drug screening. Research efforts in the past few years have transformed our understanding of the structure and multifaceted roles of the cells and their intricate crosstalk in development and disease pathogenesis. In this review, we present a new wave of technologies that include glomerulus-on-a-chip, three-dimensional microfluidic models, and organoids all promising to improve our understanding of glomerular biology and to enable the development of GFB-targeted therapies. Here, we also outline the challenges and the opportunities of these emerging biomimetic systems that aim to recapitulate the complex glomerular filter, and the evolving perspectives on the sophisticated repertoire of cellular signaling that comprise the glomerular milieu.

Formation of the largest galactic cores through binary scouring and gravitational wave recoil

ABSTRACT Massive elliptical galaxies are typically observed to have central cores in their projected radial light profiles. Such cores have long been thought to form through ‘binary scouring’ as supermassive black holes (SMBHs), brought in through mergers, form a hard binary and eject stars from the galactic centre. However, the most massive cores, like the $\sim 3{\, \mathrm{kpc}}$ core in A2261-BCG, remain challenging to explain in this way. In this paper, we run a suite of dry galaxy merger simulations to explore three different scenarios for central core formation in massive elliptical galaxies: ‘binary scouring’, ‘tidal deposition’, and ‘gravitational wave (GW) induced recoil’. Using the griffin code, we self-consistently model the stars, dark matter, and SMBHs in our merging galaxies, following the SMBH dynamics through to the formation of a hard binary. We find that we can only explain the large surface brightness core of A2261-BCG with a combination of a major merger that produces a small $\sim 1{\, \mathrm{kpc}}$ core through binary scouring, followed by the subsequent GW recoil of its SMBH that acts to grow the core size. Key predictions of this scenario are an offset SMBH surrounded by a compact cluster of bound stars and a non-divergent central density profile. We show that the bright ‘knots’ observed in the core region of A2261-BCG are best explained as stalled perturbers resulting from minor mergers, though the brightest may also represent ejected SMBHs surrounded by a stellar cloak of bound stars.

Observations and spectral modelling of the narrow-lined Type Ic SN 2017ein

ABSTRACT SN 2017ein is a narrow-lined Type Ic SN that was found to share a location with a point-like source in the face on spiral galaxy NGC 3938 in pre-supernova images, making SN 2017ein the first credible detection of a Type Ic progenitor. Results in the literature suggest that this point-like source is likely a massive progenitor of 60–80 M⊙, depending on if the source is a binary, a single star, or a compact cluster. Using new photometric and spectral data collected for 200 d, including several nebular spectra, we generate a consistent model covering the photospheric and nebular phase using a Monte Carlo radiation transport code. Photospheric phase modelling finds an ejected mass 1.2–2.0 M⊙ with an Ek of ∼(0.9 ± 0.2) × 1051 erg, with approximately 1 M⊙ of material below 5000 km s−1 found from the nebular spectra. Both photospheric and nebular phase modelling suggests a 56Ni mass of 0.08–0.1 M⊙. Modelling the [O i] emission feature in the nebular spectra suggests that the innermost ejecta are asymmetric. The modelling results favour a low-mass progenitor of 16–20 M⊙, which is in disagreement with the pre-supernova derived high-mass progenitor. This contradiction is likely due to the pre-supernova source not representing the actual progenitor.

Multiscale Modeling of EEG/MEG Response of a Compact Cluster of Tightly Spaced Pyramidal Neocortical Neurons

In this study, the boundary element fast multipole method or BEM-FMM is applied to model compact clusters of tightly spaced pyramidal neocortical neurons firing simultaneously and coupled with a high-resolution macroscopic head model. The algorithm is capable of processing a very large number of surface-based unknowns along with a virtually unlimited number of elementary microscopic current dipole sources distributed within the neuronal arbor.The realistic cluster size may be as large as 10,000 individual neurons, while the overall computation times do not exceed several minutes on a standard server. Using this approach, we attempt to establish how well the conventional lumped-dipole model used in electroencephalography/magnetoencephalography (EEG/MEG) analysis approximates a compact cluster of realistic neurons situated either in a gyrus (EEG response dominance) or in a sulcus (MEG response dominance).

Search for Ancestral Features in Genomes of Rhizobium leguminosarum bv. viciae Strains Isolated from the Relict Legume Vavilovia formosa

Vavilovia formosa is a relict leguminous plant growing in hard-to-reach habitats in the rocky highlands of the Caucasus and Middle East, and it is considered as the putative closest living relative of the last common ancestor (LCA) of the Fabeae tribe. Symbionts of Vavilovia belonging to Rhizobium leguminosarum bv. viciae compose a discrete group that differs from the other strains, especially in the nucleotide sequences of the symbiotically specialised (sym) genes. Comparison of the genomes of Vavilovia strains with the reference group composed of R. leguminosarum bv. viciae strains isolated from Pisum and Vicia demonstrated that the vavilovia strains have a set of genomic features, probably indicating the important stages of microevolution of the symbiotic system. Specifically, symbionts of Vavilovia (considered as an ancestral group) demonstrated a scattered arrangement of sym genes (>90 kb cluster on pSym), with the location of nodT gene outside of the other nod operons, the presence of nodX and fixW, and the absence of chromosomal fixNOPQ copies. In contrast, the reference (derived) group harboured sym genes as a compact cluster (<60 kb) on a single pSym, lacking nodX and fixW, with nodT between nodN and nodO, and possessing chromosomal fixNOPQ copies. The TOM strain, obtained from nodules of the primitive “Afghan” peas, occupied an intermediate position because it has the chromosomal fixNOPQ copy, while the other features, the most important of which is presence of nodX and fixW, were similar to the Vavilovia strains. We suggest that genome evolution from the ancestral to the derived R. leguminosarum bv. viciae groups follows the “gain-and-loss of sym genes” and the “compaction of sym cluster” strategies, which are common for the macro-evolutionary and micro-evolutionary processes. The revealed genomic features are in concordance with a relict status of the vavilovia strains, indicating that V. formosa coexists with ancestral microsymbionts, which are presumably close to the LCA of R. leguminosarum bv. viciae.

The double population of Chamaeleon I detected by Gaia DR2

Context. Chamaeleon I represents an ideal laboratory to study the cluster formation in a low-mass environment. Recently, two sub-clusters spatially located in the northern and southern parts of Chamaeleon I were found with different ages and radial velocities. Aims. In this Letter we report new insights into the structural properties, age, and distance of Chamaeleon I based on the astrometric parameters from Gaia data release 2 (DR2). Methods. We identified 140 sources with a reliable counterpart in the Gaia DR2 archive. We determined the median distance of the cluster using Gaia parallaxes and fitted the distribution of parallaxes and proper motions assuming the presence of two clusters. We derived the probability of each single source of belonging to the northern or southern sub-clusters, and compared the HR diagram of the most probable members to pre-main sequences isochrones. Results. The median distance of Chamaeleon I is ~190 pc. This is consistent with the revised estimate using the Tycho-Gaia Astrometric Solution, but it is about 20 pc larger than the value commonly adopted in the literature. From a Kolmogorov–Smirnov test of the parallaxes and proper-motion distributions we conclude that the northern and southern clusters do not belong to the same parent population. The northern population has a distance dN = 192.7+0.4−0.4pc, while the southern one dS = 186.5+0.7−0.7pc. The two sub-clusters appear coeval, at variance with literature results, and most of the sources are younger than 3 Myr. The northern cluster is more elongated and extends towards the southern direction partially overlapping with the more compact cluster located in the south. A hint of a relative rotation between the two sub-clusters is also found.

An experimental study of the dynamics of ascent of the bubble system in the presence of a surfactant

This paper presents investigations on the new experimental setup for obtaining a compact cluster of monodisperse bubbles of a given diameter is presented. Also we provided the results of experimental study of the bubble cluster floating-up in the presence of a surfactant in a wide range of Reynolds numbers. There was held a comparison of the dynamics of the floating-up of a monodisperse bubble cluster in a glycerol medium and in the medium glycerin supplemented with a surfactant.

Experimental setup for investigating the dynamics of the ascent of a cluster of bubbles in a liquid

There is a scheme of experimental setup providing preparation of the compact cluster of monodispersed bubbles of the given diameter presented in the work. Further, in this research we have calculated setup parameters that are necessary for preparation of the compact air bubble cluster in glycerin at room temperature.