Biology subjects

Grover, R.

Publications and source records attributed to Grover, R..

10 recordsLinked to original sources

bioRxiv2026

Novel Evidence for Nitrogen-Dependent Regulation of Nitrate Reductase in Coral Symbiosis

The nutritional symbiosis between corals and their photosynthetic dinoflagellate partners underpins the ecological success of reef-building corals in nutrient-poor environments. Although coral holobionts can assimilate the abundant yet highly variable environmental nitrate, direct insight into how nitrate reductase is regulated in these symbiotic algae has been lacking. Here, we provide the first characterization of nitrate reductase protein and gene expression in cultured Symbiodiniaceae exposed to different nitrogen sources and light regimes, revealing the multifactorial nature of its regulation. We demonstrate that nitrate reductase operates as a substrate-induced enzyme: nitrate stimulates protein synthesis in nitrogen-starved cultures, whereas ammonium actively suppresses its expression in a concentration-dependent manner. Light availability and photosynthetic electron transport further modulate protein abundance, suggesting that while nitrate reductase synthesis depends on nitrate availability, its stability may rely on photosynthesis. We also show that nitrate reductase is synthesized within hours of nitrate exposure by symbionts from nitrogen-starved corals, demonstrating that nitrate reduction can occur within the host environment. However, this response is transient and diminished relative to free-living cells, indicating that nitrate reduction is a facultative pathway activated when preferred nitrogen sources are limited. Finally, gene expression measurements and pharmacological inhibition confirm that nitrate reductase regulation is predominantly post-transcriptional, enabling this rapid and reversible control of nitrate assimilation. Together, these findings reveal a tightly regulated and responsive nitrate reduction system in coral symbionts that provides a flexible mechanism contributing to nitrogen homeostasis under fluctuating nutrient regimes.

Molecular Biology↗

bioRxiv2025

Microtubule lattice defects facilitate spastin-mediated severing

The length regulation of microtubules and their organization into complex arrays inside cells occurs through the activity of polymerases, depolymerases as well as severing enzymes such as katanin and spastin. The latter hexamerize on the microtubule lattice, pull out single tubulin dimers in an ATP-dependent manner and eventually generate internal breaks in the microtubule. While both, katanin and spastin, were shown to be regulated by posttranslational tubulin modifications, only katanin was reported to have microtubule lattice-defect- or crossover-sensing activity. Here, we employ in vitro assays to investigate the impact of microtubule lattice defects on the severing characteristics of spastin. Toward this end, we prepared GMPCPP-stabilized microtubules with varying defect densities. Thereby, microtubule defects were introduced either through specific polymerization conditions or by end-to-end annealing of microtubules. We found that (i) the presence of defects accelerated the onset of the severing process and (ii) severing was twice as frequent in microtubule segments with defect sites as compared to random lattice segments. However, there was no evidence of preferential binding of spastin to defect sites. We therefore propose a severing mechanism in which defects do not actively promote microtubule severing but rather passively contribute to microtubule lattice instability, facilitating the process as fewer tubulin subunits are required to be removed for microtubule severing.

biophysics↗

bioRxiv2025

Altered lysosomal biology impairs motor neuron survival via TFEB dysregulation in spinal muscular atrophy

Spinal muscular atrophy (SMA) is a devastating motor neuron disease, caused by recessive mutations or deletions of the SMN1 gene, representing the leading genetic cause of infant mortality. Available therapies, aimed at increasing SMN protein levels, can only partially halt motor neuron (MN) degeneration in a select number of patients, reinforcing the need for combinatorial treatments to improve clinical outcomes. We previously showed that mTORC1 overactivation and impaired autophagosome clearance in SMA MNs lead to the accumulation of protein aggregates, contributing to MN degeneration. However, the mechanistic link between SMN protein deficiency and autophagy-lysosomal dysfunction remained unknown. Here, using patient iPSC-derived MNs along with isogenic and healthy controls, we show that SMA MNs exhibit reduced lysosome numbers and impaired functionality. Furthermore, the master regulator of lysosomal biogenesis and autophagy, TFEB, is downregulated, and its nuclear translocation compromised upon SMN deficiency. We further propose the upregulation of the mTORC1 positive modulator TPT1 as contributor to TFEB dysregulation. Notably, TFEB overexpression ameliorates protein aggregate accumulation in SMA MNs and enhances MN survival both in vitro and in a zebrafish SMA model. Our findings identify lysosomal dysfunction as a key player in SMA pathology and highlight TFEB activation as a potential therapeutic strategy for SMA treatment. One Sentence SummaryTFEB activation restores lysosomal function and improves motor neuron survival in SMA, highlighting its potential as a therapeutic target.

neuroscience↗

bioRxiv2024

A floor-field model of tau-taxol competition explains tau envelope dynamics on taxol-stabilized microtubules

Tau is a microtubule-associated protein (MAP) that is highly expressed in neurons. Recent in-vitro studies have shown that tau molecules can segregate into cohesive envelopes on paclitaxel (taxol) stabilized microtubules. These envelopes act as selective barriers gating the motor transport and protecting microtubules against the action of severing enzymes. However, the mechanisms underlying the formation of these envelopes remain unclear. Recent in vitro reconstitution assays revealed that the formation of tau envelopes induces a compaction of the underlying microtubule lattice, whereas taxol binding induces lattice expansion, indicating competitive binding between tau and taxol on microtubules. In this study, we use physical modeling to investigate how this competition between tau and taxol regulates the formation of tau envelopes. Our model includes static and dynamic floor-fields, concepts adapted from pedestrian dynamics. By comparing our simulation results with experimental data, we demonstrate that tau-taxol competition on the microtubule lattice is sufficient to explain the features of the formation and disassembly of tau envelopes. Notably, tau-tau interactions are not necessary to account for the steadiness of these envelopes.

biophysics↗

bioRxiv2024

Tau accelerates tubulin exchange in the microtubule lattice

Microtubules are cytoskeletal filaments that exhibit dynamic tip instability and, as recent discoveries reveal, possess a dynamic lattice undergoing continuous tubulin loss and incorporation. In this study, we investigate the role of tau, a neuronal microtubule-associated protein (MAP) known for its stabilizing effects on microtubules, in modulating lattice dynamics. Using in vitro reconstitution, kinetic Monte Carlo modeling, and molecular dynamics simulations, we reveal that tau, despite lacking enzymatic activity, accelerates tubulin exchange within the lattice, particularly at topological defect sites. Tau appears to stabilize longitudinal tubulin-tubulin interactions while destabilizing lateral ones, thereby enhancing the mobility and repair of lattice defects. These results challenge the traditional view of tau as merely a stabilizer, uncovering its active role in dynamically modulating microtubule lattice structure.

biophysics↗

bioRxiv2024

Intellectual disability-causing mutations in KIF11 impair microtubule dynamics and dendritic arborization

Precise control of axonal and dendritic architecture is vital for proper brain function, with microtubule (MT) dynamics playing a central role in this process. Here, we uncover a previously unrecognized function of the molecular motor protein KIF11, which acts as a MT dynamics rheostat in hippocampal neurons to modulate dendritic branching. Known for its role in mitotic spindle bipolarity, KIF11 is also implicated in Microcephaly with or without chorioretinopathy, lymphedema, or intellectual disabilities (MCLID). However, the specific neuronal functions of KIF11 and the impact of its mutations in MCLID have remained largely unexplored. Our studies, using quantitative imaging of MT dynamics following KIF11 inhibition, indicate that KIF11 preferentially binds to parallel MTs in mature neurons. This binding is associated with a marked increase in minus-end-out MT dynamics in both axons and dendrites upon KIF11 loss of function, coupled with enhanced MT flux and extended growth in tertiary dendrites. These changes suggest a novel role for KIF11 in orchestrating dendritic branching. Moreover, introducing MCLID-associated KIF11 mutations, KIF11Y82F, and KIF11{Delta}Cterm, which cause minor microcephaly but severe intellectual disabilities, leads to significantly reduced MT dynamics and impaired dendritic arborization. In a microtubule sliding assay, KIF11Y82F significantly reduced KIF11 velocity while KIF11{Delta}Cterm increased it. Temporal inhibition of KIF11 using a photo-inhibitable KIF11, show increased MT dynamics and dendritic growth, while activation results in kinked and twisted branches. Together, these data reveal that KIF11 is MT dynamics rheostat and regulator of dendritic arborization in mature neurons and provide new insights into the molecular mechanisms driving MCLID.

neuroscience↗

bioRxiv2023

Restoring adiponectin via rosiglitazone ameliorates tissue wasting in mice with lung cancer.

The cancer associated cachexia syndrome (CACS) is a systemic metabolic disorder resulting in loss of body weight due to skeletal muscle and adipose tissues atrophy. CACS is particularly prominent in lung cancer patients, where it contributes to poor quality of life and excess mortality. Using the Kras/Lkb1 (KL) mouse model, we found that CACS is associated with white adipose tissue (WAT) dysfunction that directly affects skeletal muscle homeostasis. WAT transcriptomes showed evidence of reduced adipogenesis, and, in agreement, we found low levels of circulating adiponectin. To preserve adipogenesis and restore adiponectin levels, we treated mice with the PPAR-{gamma} agonist, rosiglitazone. Rosiglitazone treatment increased serum adiponectin levels, delayed weight loss, and preserved skeletal muscle and adipose tissue mass, as compared to vehicle-treated mice. The preservation of muscle mass with rosiglitazone was associated with increases in AMPK and AKT activity. Similarly, activation of the adiponectin receptors in muscle cells increased AMPK activity, anabolic signaling, and protein synthesis. Our data suggest that PPAR-{gamma} agonists may be a useful adjuvant therapy to preserve tissue mass in lung cancer. Key points- The PPAR-{gamma} agonist, rosiglitazone, restores circulating adiponectin levels in mice with lung cancer. - Rosiglitazone preserves skeletal muscle and adipose tissue mass in mice with lung cancer. - The preservation of muscle mass with rosiglitazone is associated with increases in AMPK and AKT activity. - Stimulation of adiponectin signaling increases AMPK activity, anabolic signaling, and protein synthesis in muscle cell culture.

cancer biology↗

bioRxiv2022

Vesicles driven by dynein and kinesin exhibit directional reversals without external regulators

Intracellular transport along cytoskeletal filaments propelled by molecular motors ensures the targeted delivery of cargoes to their destinations. Such transport is rarely unidirectional but rather bidirectional, including intermittent pauses and directional reversals owing to the simultaneous presence of opposite-polarity motors. It has been unclear whether such a complex motility pattern results from the sole mechanical interplay between opposite-polarity motors or requires external regulators. Here, we addressed this outstanding question by reconstituting cargo motility along microtubules in vitro by attaching purified Dynein-Dynactin-BICD2 (DDB) and kinesin-3 (KIF16B) to large unilamellar vesicles. Strikingly, we found that this minimal system is sufficient to recapitulate runs, pauses and reversals similar to in vivo cargo motility. In our experiments, reversals were always preceded by vesicle pausing and the transport directionality could be tuned by the relative numbers of opposite-polarity motors on the vesicles. Unexpectedly, during all runs the vesicle velocity was not influenced by the presence of the opposing motors. To gain mechanistic insight into bidirectional transport, we developed a mathematical model which predicts that low numbers of engaged motors are critical to transition between runs and pauses. Taken together, our results suggest that motors diffusively anchored to membranous cargo transiently engage in a tug-of-war during pauses where stochastic motor attachment and detachment events can lead to directional reversals without the necessity of external regulators.

biophysics↗

bioRxiv2022

Whole exome-sequencing of vitiligo lesions indicate lower burden of somatic variations: implications in risk for non-melanoma skin cancers

Mapping of somatic variations has enabled understanding the progression of clonal variations from healthy skin to cutaneous malignancies. Highlighting, the adaptive nature of pigmentation, germline mutations in albinism amplify skin cancer susceptibility. However, lower incidence of non-melanoma skin cancer among subjects with acquired depigmenting skin disorder vitiligo is enigmatic and a matter of longstanding debate. To address this, we performed high-coverage exome sequencing of matched non-lesional and lesional vitiligo skin along with whole blood to account for germline variations. Our analysis suggests lower burden of somatic cancer-associated variations in exposed depigmented lesional skin compared to the non-lesional skin. A detailed investigation of vitiligo skin transcriptome reveals elevation of DNA repair and cell-proliferation pathways. Validation by comet-assay for DNA damage and cell cycle analysis of epidermal cells suggest undamaged DNA in vitiligo lesions that could be attributed to higher proliferation-coupled repair. Endorsing this, UV-signature variations are not prominent, instead SBS5 associated with endogenous mutational processes is conspicuous in both the vitiligo tissues. Our systematic pilot study indicates lower somatic mutation burden in vitiligo skin and supports the earlier demographic observation on lower risk of non-melanoma skin cancer in vitiligo subjects, providing an opportunity to learn strategies for cancer prevention from vitiligo. Brief SummaryVitiligo skin harbors decreased somatic variation burden in cancer-associated genes and a concomitant augmentation in DNA repair response, explaining the lower incidence of cutaneous malignancies.

genomics↗

bioRxiv2018

Effect of feeding and thermal stress on photosynthesis, respiration and the carbon budget of the scleractinian coral Pocillopora damicornis

Studying carbon dynamics in the coral holobiont provides essential knowledge of nutritional strategies and is thus central to understanding coral ecophysiology. In this study, the first aim was to investigate the effect of daily feeding and thermal stress on oxygen (O2) rates measured at polyp-scale with microsensors and at whole fragment scale using incubation methods. The second aim was to assess the carbon budget of the symbiotic association using H13CO3, under the different conditions. Micro- and macro-scale measurements revealed enhanced O2 evolution rates for fed compared to unfed corals. However, gross O2 production in fed corals was increased at high temperature on a macroscale but not on a microscale basis, likely due to a heterogeneous distribution of photosynthesis over the coral surface. Starved corals always exhibited reduced photosynthetic activity at high temperature, which suggests that the nutritional status of the coral host is a key limiting factor for coral productivity under thermal stress. Quantification of photosynthate translocation and carbon budgets showed very low incorporation rates, for both symbionts and host (0.03 - 0.6 g C cm-2 h-1) equivalent to only 0.008 - 0.6 %, of the photosynthetically fixed carbon for P. damicornis, in all treatments. Carbon loss (via respiration and/or mucus release) was about 41 - 47 % and 52 - 76% of the fixed carbon for starved and fed corals, respectively. Such high loss of translocated carbon suggests that P. damicornis is nitrogen and/or phosphorus limited. Heterotrophy might thus cover a larger portion of the nutritional demand for P. damicornis than previously assumed. Our results suggest that active feeding plays a fundamental role in metabolic dynamics and bleaching susceptibility of corals.

ecology↗