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result(s) for
"Acharya, Nischal"
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NELL2-Robo3 complex structure reveals mechanisms of receptor activation for axon guidance
Axon pathfinding is critical for nervous system development, and it is orchestrated by molecular cues that activate receptors on the axonal growth cone. Robo family receptors bind Slit guidance cues to mediate axon repulsion. In mammals, the divergent family member Robo3 does not bind Slits, but instead signals axon repulsion from its own ligand, NELL2. Conversely, canonical Robos do not mediate NELL2 signaling. Here, we present the structures of NELL-Robo3 complexes, identifying a mode of ligand engagement for Robos that is orthogonal to Slit binding. We elucidate the structural basis for differential binding between NELL and Robo family members and show that NELL2 repulsive activity is a function of its Robo3 affinity and is enhanced by ligand trimerization. Our results reveal a mechanism of oligomerization-induced Robo activation for axon guidance and shed light on Robo family member ligand binding specificity, conformational variability, divergent modes of signaling, and evolution.
Robo3 is a divergent, multifunctional member of the Robo receptor family that mediates axon guidance by its ligand NELL2 instead of the canonical Slit ligands. Here, the authors present the crystal structures of human Robo3 in complex with NELL1 and NELL2, and they show through biophysical and functional assays how NELL-Robo3 affinity and ligand-induced receptor multimerization control axon guidance activity.
Journal Article
Potential of Biochar-Based Organic Fertilizers on Increasing Soil Fertility, Available Nutrients, and Okra Productivity in Slightly Acidic Sandy Loam Soil
Reducing chemical fertilizers is critical for maintaining soil health and minimizing environmental damage. Biochar-based organic fertilizers reduce fertilizer inputs, improve soil fertility, increase crop productivity, and reduce environmental risks. In this study, a pot experiment was conducted in a greenhouse to assess the potential of biochar-based organic and inorganic fertilizers to improve soil fertility and Okra yield. Seven treatments with three replicates were arranged in a completely randomized design (CRD). Three treatments included biochar-blended formulations (i) biochar mixed with mineral NPK fertilizer (BF), (ii) biochar mixed with vermicompost (BV), and (iii) biochar mixed with goat manure (BM); two treatments included biochar enrichment formulations (iv) biochar enriched with cow urine (BCU) and (v) biochar enriched with mineral NPK fertilizer in aqueous solution (BFW), and the remaining two included control treatments; (vi) control (CK: no biochar and no fertilizers) and (vii) fertilized control (F: only recommended NPK fertilizer and no biochar). Mineral NPK fertilizers in BF, BFW, and F were applied at the recommended rate as urea, di-ammonium phosphate (DAP), and muriate of potash (MOP). Organic fertilizers in BV, BM, and BCU treatments were applied in equal quantities. All biochar-amended treatments showed improved soil chemical properties with higher pH, organic carbon, total N, and available P and K compared to the two non-biochar control plots (CK and F). Biochar blended with goat manure (BM) showed the highest effect on soil fertility and fruit yield. BM (51.8 t ha−1) increased fruit yield by 89% over CK (27.4 t ha−1) and by 88% over F (27 t ha−1). Similarly, cow urine-enriched biochar (BCU) (35 t ha−1) increased fruit yield by 29% and 28% compared to CK and F, respectively. Soil pH, OC, and nutrient availability (total N, available P, and available K) showed a significantly positive relationship with fruit yield. The study suggests that using biochar-based organic fertilizers, such as BCU and BM, could outperform recommended mineral fertilizers (F) and produce higher yields and healthy soils, thereby contributing to mitigating the current food security and environmental concerns of the country.
Journal Article
No evidence for quenching in quasars
The role of quasar feedback in galaxy evolution remains poorly understood. Throughout this work, we explore the effects of negative feedback on star formation in quasar host galaxies, analysing two distinct populations of quasars. The first is a sample of high-redshift (z > 2) low-ionisation broad absorption line quasars (LoBALs) - a class of quasars hosting energetic mass outflows, in which we find evidence for prolific star formation (>750Mʘyr–1) exceeding that of non-BAL quasars at the same redshift. The second is a population of 207 low-redshift (z < 0.3) quasars, in which we find an enhancement in the SFRs of quasar hosts compared to the underlying galaxy population, with no quasars residing in quiescent hosts over the last 2Gyr. Overall, we find no evidence for galaxy-wide quenching in either population, rather we suggest that the dominant effect of quasar activity is to enhance star formation in the galaxy.
Journal Article
Accretion properties of X-ray AGN: Evidence for radiation-regulated obscuration with redshift-dependent host galaxy contribution
We adopt a Bayesian X-ray spectral approach to investigate the accretion properties of unobscured (\\(20<\\log(N_{\\rm H}/{\\rm cm}^{-2}<22\\)) and obscured (\\(22< \\log(N_{\\rm H}/{\\rm cm}^{-2}<24\\)) active galactic nuclei (AGN) to shed light on the orientation vs evolution scenarios for the origin of the obscuring material. For a sample of 3882 X-ray-selected AGN from the {\\it Chandra} COSMOS Legacy, AEGIS and CDFS extragalactic surveys, we constrain their stellar masses, \\(M_\\star\\), intrinsic X-ray luminosities, \\(L_{\\rm X}\\), obscuring column densities, \\(N_{\\rm H}\\), and specific accretion rates \\(\\lambda\\propto L_{\\rm X}/M_\\star\\). By combining these observables within a Bayesian non-parametric approach, we infer, for the first time, the specific accretion rate distribution (SARD) of obscured and unobscured AGN to \\(z\\approx3\\), i.e. the probability of a galaxy with mass \\(M_\\star\\) at redshift \\(z\\) hosting an AGN with column density \\(N_{\\rm H}\\) and specific accretion rate \\(\\lambda\\). Our findings indicate that (1) both obscured and unobscured SARDs share similar shapes, shifting towards higher accretion rates with redshift, (2) unobscured SARDs exhibit a systematic offset towards higher \\(\\lambda\\) compared to obscured SARD for all redshift intervals, (3) the obscured AGN fraction declines sharply at \\(\\log\\lambda_{\\rm break} \\sim-2\\) for \\(z <0.5\\), but shifts to higher \\(\\lambda\\) values with increasing redshift, (4) the incidence of AGN within the theoretically unstable blow-out region of the \\(\\lambda-N_{\\rm H}\\) plane increases with redshift. These observations provide compelling evidence for AGN \"downsizing\" and radiation-regulated nuclear-scale obscuration with an increasing host galaxy contribution towards higher redshifts.
Paper
Galaxy and Mass Assembly (GAMA): Low-redshift Quasars and Inactive Galaxies Have Similar Neighbors
We explore the properties of galaxies in the proximity (within a \\(\\sim\\)2 Mpc radius sphere) of Type I quasars at 0.1
Paper
The miniJPAS Survey: The radial distribution of star formation rates in faint X-ray active galactic nuclei
We study the impact of black hole nuclear activity on both the global and radial star formation rate (SFR) profiles in X-ray-selected active galactic nuclei (AGN) in the field of miniJPAS, the precursor of the much wider J-PAS project. Our sample includes 32 AGN with z < 0.3 detected via the XMM-Newton and Chandra surveys. For comparison, we assembled a control sample of 71 star-forming (SF) galaxies with similar magnitudes, sizes, and redshifts. To derive the global properties of both the AGN and the control SF sample, we used CIGALE to fit the spectral energy distributions derived from the 56 narrowband and 4 broadband filters from miniJPAS. We find that AGN tend to reside in more massive galaxies than their SF counterparts. After matching samples based on stellar mass and comparing their SFRs and specific SFRs (sSFRs), no significant differences appear. This suggests that the presence of AGN does not strongly influence overall star formation. However, when we used miniJPAS as an integral field unit (IFU) to dissect galaxies along their position angle, a different picture emerges. We find that AGN tend to be more centrally concentrated in mass with respect to SF galaxies. Moreover, we find a suppression of the sSFR up to 1Re and then an enhancement beyond 1Re , strongly contrasting with the decreasing radial profile of sSFRs in SF galaxies. This could point to an inside-out quenching of AGN host galaxies. These findings suggest that the reason we do not see differences on a global scale is because star formation is suppressed in the central regions and enhanced in the outer regions of AGN host galaxies. While limited in terms of sample size, this work highlights the potential of the upcoming J-PAS as a wide-field low-resolution IFU for thousands of nearby galaxies and AGN.
Paper
Molecular basis for substrate recruitment to the PRMT5 methylosome
PRMT5 is an arginine methyltransferase and a therapeutic target in MTAP null cancers. PRMT5 utilizes adaptor proteins for substrate recruitment through a previously undefined mechanism. Here, we identify an evolutionarily conserved peptide sequence shared among the three known substrate adaptors (pICln/CLNS1A, RIOK1 and COPR5) and show it is necessary and sufficient for interaction with PRMT5. We structurally resolve the interface with PRMT5 and show via genetic perturbation that it is required for methylation of adaptor-recruited substrates including the spliceosome, histones, and ribosome assembly complexes. Genetic disruption of the PRMT5-substrate adaptor interface leads to a hypomorphic decrease in growth of MTAP null tumor cells and is thus a novel site for development of therapeutic inhibitors of PRMT5.
Paper
Getting there and staying there: supporting and enabling persistent human life on Mars using synthetic natural rubber, self-healing materials, and biological batteries
Planetary exploration requires a balance between preemptive planning and financial feasibility. The risk of mid-mission equipment failure, power shortages, or supply depletion incentivizes precautionary measures, but the financial strain of sending unnecessary mass into space limits this practice. To balance the two, our team explored the advantages of biological solutions, namely the self-sustaining abilities of low-mass organisms, to make planetary exploration more self-sufficient and economical. Prioritizing repair over replacement, we are developing self-healing materials embedded with Bacillus subtilis. For longer-lasting energy, we are designing a \"biobactery\" using linearly oriented Escherichia coli to generate power. For renewable materials, we are engineering bacteria to synthesize and degrade rubber. Individually, these projects offer sustainable alternatives for repair, power, and materials. But when combined, these consolidated insights can provide us with the power to get to Mars and resources to sustain us while we're there.
Paper