Biology subjects

Ananthanarayanan, V.

Publications and source records attributed to Ananthanarayanan, V..

11 recordsLinked to original sources

bioRxiv2026

Mitochondrial morphology and function are tuned by microtubule association

Mitochondrial morphology is regulated through dynamic fission and fusion processes that are critical for cellular metabolism and homeostasis. Microtubules and mitochondria are functionally coupled across many cellular contexts, yet the mechanistic basis of this relationship remains poorly understood. Here, we reveal that microtubule association is a key regulator of mitochondrial morphology and function. Pharmacological or genetic manipulation of microtubule dynamics controls mitochondrial membrane potential and respiratory capacity, with stabilisation driving elongation, and depolymerisation triggering Drp1-dependent fission and reduced respiration. Strikingly, we identify increased microtubule polymerisation as a hallmark of starvation-induced mitochondrial hyperfusion, a key adaptive response to nutrient stress, and show that this expanded microtubule network is an essential prerequisite for the starvation response. We demonstrate that this regulation operates independently of canonical tubulin post-translational modifications that stabilise microtubules. Rather, increased mitochondria-microtubule association, driven by network expansion, is both necessary and sufficient to drive mitochondrial hyperfusion, as demonstrated by forced mitochondria-microtubule tethering. Taken together, our findings establish microtubule binding as a key upstream regulator of mitochondrial network dynamics, with direct implication for understanding how cells coordinate cytoskeletal organisation with metabolic adaptation during physiological stress.

Cell Biology↗

bioRxiv2025

Integrative analysis of spatiotemporal transcriptomics delineates dynamic cell states in squamous tumorigenesis

Squamous cell cancers are responsible for 1 in 5 cancer deaths and survival improvements lag behind those seen in adenocarcinomas. This disparity is in large part due to the limited impact of immunotherapy due to therapeutic resistance, where less than ten percent of patients respond in early stage squamous cell carcinomas of the Head and Neck. Mechanisms that govern intrinsic resistance remain poorly understood and likely arise during the premalignant or dysplastic state. Here, we generated a dataset of murine and human oral squamous epithelia spanning the earliest premalignant stages through invasive carcinoma. Integrative analysis of single-cell and spatial transcriptomics data across the dysplasia to carcinoma continuum reveals early and sustained shifts in epithelial transcriptomes. Spatially informed cell-cell interaction analysis reveals dysplasia-specific upregulation of wound healing and immune remodeling programs in severe dysplasia and invasive carcinoma in a human sample of oral dysplasia. The presence of these transcriptomic programs within early dysplasia may account for the aggressive clinical presentations of squamous cancers including intrinsic therapeutic resistance.

cancer biology↗

bioRxiv2025

Mitochondrial function regulates cell growth kinetics to actively maintain mitochondrial homeostasis

Mitochondria are not produced de novo in newly divided daughter cells, but are inherited from the mother cell during mitosis. While mitochondrial homeostasis is crucial for living cells, the feedback responses that maintain mitochondrial volume across generations of dividing cells remain elusive. Here, using a microfluidic yeast mother machine, we tracked several generations of fission yeast cells and observed that cell size and mitochondrial volume grew exponentially during the cell cycle. We discovered that while mitochondrial homeostasis relied on the sizer mechanism of cell size maintenance, mitochondrial function was a critical determinant of the timing of cell division: cells born with lower than average amounts of mitochondria grew slower and thus added more mitochondria before they divided. Thus, mitochondrial addition during the cell cycle was tailored to the volume of mitochondria at birth, such that all cells ultimately contained the same mitochondrial volume at cell division. Quantitative modelling and experiments with mitochondrial DNA-deficient rho0 cells additionally revealed that mitochondrial function was essential for driving the exponential growth of cells. Taken together, we demonstrate a central role for mitochondrial activity in dictating cellular growth rates and ensuring mitochondrial volume homeostasis.

cell biology↗

bioRxiv2023

Women's representation in Indian academia and conferences

Abstract/IntroductionIndian science academia has a dearth of women researchers at all levels. Not only are they under-represented, but they are also under-highlighted, under-mentored and overlooked for awards, grants and other career-advancing steps. To effectively address this problem and devise a solution for the inequity, we need data on the proportion of women faculty across multiple STEM institutions. Such a database, currently, does not exist. To fill this gap, we formed BiasWatchIndia to (1) document the inequities, and (2) provide real-time actionable data as a basis for future remedial steps. Along with collecting data on women representation at the faculty level in Indian STEM (science, technology, engineering and mathematics) academia, BiasWatchIndia also helps highlight the lack of women representation and gender imbalance in Indian STEM talks, conferences, workshops and panels. Based on our findings, we recommend several measures that need to be implemented by universities and institutes to challenge the status quo changes for women in Indian academia.

scientific communication and education↗

bioRxiv2023

Pathogenic aggregates alter actin organization and cellular viscosity resulting in stalled clathrin mediated endocytosis

Protein aggregation is a common underlying feature of neurodegenerative disorders. Cells expressing neurodegeneration-associated mutant proteins show altered uptake of ligands, suggestive of impaired endocytosis, in a manner as yet unknown. Using live cell imaging, we show that clathrin-mediated endocytosis (CME) is affected due to altered actin cytoskeletal organization in the presence of Huntingtin aggregates. Additionally, we find that cells containing Huntingtin aggregates are stiffer and less viscous than their wild-type counterparts due to altered actin conformation, and not merely due to the physical presence of aggregate(s). We further demonstrate that CME and cellular viscosity can be rescued by overexpressing Hip1, Arp2/3 or transient LatrunculinA treatment. Examination of other pathogenic aggregates revealed that only a subset of these display defective CME, along with altered actin organization and increased stiffness. Together, our results point to an intimate connection between functional CME, actin organization and cellular stiffness in the context of neurodegeneration.

cell biology↗

bioRxiv2022

Precision super-resolution cryo-correlative light and electron microscopy for rapid in situ structural analyses of optogenetically-positioned organelles

Unambiguous targeting of cellular structures for in situ cryo-electron microscopy in the heterogeneous, dense, and compacted environment of the cytoplasm remains challenging. Here we have developed a novel cryogenic correlative light and electron microscopy (cryo-CLEM) workflow which combines thin cells grown on a mechanically defined substratum to rapidly analyse organelles and macromolecular complexes in the cell by cryo-electron tomography (cryo-ET). We coupled these advancements with optogenetics to redistribute perinuclear-localised organelles to the cell periphery for cryo-ET. This reliable and robust workflow allows for fast in situ analyses without the requirement for cryo-focused ion beam milling. We have developed a protocol where cells can be frozen, imaged by cryo-fluorescence microscopy and ready for batch cryo-ET within a day.

cell biology↗

bioRxiv2021

Microtubule-mitochondrial attachment determines cell division symmetry and polarity in fission yeast

Association with microtubules inhibits the fission of mitochondria in Schizosachharomyces pombe. Here we show that this attachment of mitochondria to microtubules is an important cell intrinsic factor in determining division symmetry. By comparing mutant cells that exhibited enhanced attachment and no attachment of mitochondria to microtubules (Dnm1{Delta} and Mmb1{Delta} respectively), we show that microtubules in these mutants displayed aberrant dynamics compared to wild-type cells, which resulted in errors in nuclear positioning. This translated to cell division asymmetry in a significant proportion of both Dnm1{Delta} and Mmb1{Delta} cells. Asymmetric division in Dnm1{Delta} and Mmb1{Delta} cells resulted in unequal distribution of mitochondria, with the daughter cell that received more mitochondria growing faster than the other daughter. Taken together, we show the existence of homeostatic feedback controls between mitochondria and microtubules in fission yeast, which directly influence mitochondrial partitioning and thereby, cell growth.

cell biology↗

bioRxiv2021

Microtubule dynamics and the evolution of mitochondrial populations in fission yeast cells: A kinetic Monte Carlo study

Mitochondrial populations in cells are maintained by cycles of fission and fusion events. Perturbation of this balance has been observed in several diseases such as cancer and neurodegeneration. In fission yeast cells, the association of mitochondria with microtubules inhibits mitochondrial fission, [1] illustrating the intricate coupling between mitochondria and the dynamic population of microtubules within the cell. In order to understand this coupling, we carried out kinetic Monte Carlo (KMC) simulations to predict the evolution of mitochondrial size distributions for different cases; wild-type cells, cells with short and long microtubules, and cells without microtubules. Comparison are made with mitochondrial distributions reported in experiments with fission yeast cells. Using experimentally determined mitochondrial fission and fusion frequencies, simulations implemented without the coupling of microtubule dynamics predicted an increase in the mean number of mitochondria, equilibrating within 50 s. The mitochondrial length distribution in these models also showed a higher occurrence of shorter mitochondria, implying a greater tendency for fission, similar to the scenario observed in the absence of microtubules and cells with short microtubules. Interestingly, this resulted in overestimating the mean number of mitochondria and underestimating mitochondrial lengths in cells with wild-type and long microtubules. However, coupling mitochondrias fission and fusion events to the microtubule dynamics effectively captured the mitochondrial number and size distributions in wild-type and cells with long microtubules. Thus, the model provides greater physical insight into the temporal evolution of mitochondrial populations in different microtubule environments, allowing one to study both the short-time evolution as observed in the experiments (<5 minutes) as well as their transition towards a steady-state (>15 minutes). Our study illustrates the critical role of microtubules in mitochondrial dynamics and that coupling their growth and shrinkage dynamics is critical to predicting the evolution of mitochondrial populations within the cell. Author summaryMitochondria are semi-autonomous organelles that undergo fission and fusion to facilitate quality control and exchange of mitochondrial mass within the cell. Impaired mitochondrial fusion and fission dynamics are associated with disease states such as cancer and neurodegeneration. Recent experiments in fission yeast cells revealed a reduction in mitochondrial fission events when mitochondria were bound to the microtubules and longer microtubules shifted the mitochondrial population to longer lengths. In a distinct departure from earlier reports [2-16], we develop a generic framework to study the evolution of the mitochondrial population in fission yeast cells to predict the observed mitochondrial population by coupling the microtubule and mitochondrial dynamics. Using kinetic Monte Carlo (KMC) simulations we predict the temporal evolution of mitochondria in both the mutated and wild-type states of microtubules in fission yeast cells. The mitochondrial population evolves due to multiple fission and fusion reactions occurring between mitochondrial species of various lengths. Several models with varying complexity have been developed to study mitochondrial evolution, and predictions of the mitochondrial populations agree well with experimental data on fission yeast cells without microtubules and cells with short, wild-type and long microtubules. These set of microtubule states are consistent with not only the microtubule dynamics typically observed in cells under different physiological stimuli such as mitosis and disease states but also the stable microtubule states obtained through post-translational modification of and {beta} tubulin subunits of microtubules. Our study reveals that the temporal evolution of mitochondrial populations is an intrinsic function of the state of microtubules which modulates the fission and fusion frequencies to maintain mitochondrial homeostasis within cells.

systems biology↗

bioRxiv2021

Single-molecule imaging of cytoplasmic dynein reveals the mechanism of motor activation and cargo capture

Cytoplasmic dynein 1 (dynein) is the primary minus end-directed motor protein in most eukaryotic cells. Dynein remains in an inactive conformation until the formation of a tripartite complex comprising dynein, its regulator dynactin and a cargo adaptor. How this process of dynein activation occurs is unclear, since it entails the formation of a three-protein complex inside the crowded environs of a cell. Here, we employed live-cell, single-molecule imaging to visualise and track fluorescently tagged dynein. First, we observed that only ~30% of dynein molecules that bound to the microtubule (MT) engaged in minus end-directed movement, and that too for a short duration of ~0.6 s. Next, using high-resolution imaging in live and fixed cells, and using correlative light and electron microscopy, we discovered that dynactin and endosomal cargo remained in proximity to each other and to MTs. We then employed two-colour imaging to visualise cargo movement effected by single motor binding. Finally, we performed long-term imaging to show short movements are sufficient to drive cargo to the perinuclear region of the cell. We then used these discoveries as the basis for a stochastic model incorporating dynamic motors binding to cargo located along MTs, and also developed a coarse-grained 3-state run- and-tumble particle (RTP) model for the cargo that quantitatively recapitulates the emergent statistics of cargo movement. Taken together, we discovered a search mechanism that is facilitated by dyneins frequent MT binding-unbinding kinetics: (1) in a futile event when dynein does not encounter cargo anchored in proximity to the MT, dynein dissociates and diffuses into the cytoplasm, (2) when dynein encounters cargo and dynactin upon MT-binding, it moves cargo in a short run. Several of these short runs are undertaken in succession for long-range directed movement. In conclusion, we demonstrate that dynein activation and cargo capture are coupled in a step that relies on the reduction of dimensionality to enable minus end-directed transport in cellulo, and that complex cargo behaviour emerges from stochastic motor-cargo interactions.

cell biology↗

bioRxiv2019

Cortical tethering of mitochondria by the dynein anchor Mcp5 enables uniparental mitochondrial inheritance during fission yeast meiosis

During sexual reproduction in eukaryotes, processes such as active degradation and dilution of paternal mitochondria ensure maternal mitochondrial inheritance. In the isogamous organism fission yeast, we employed high-resolution fluorescence microscopy to visualize mitochondrial inheritance during meiosis by differentially labeling mitochondria of the two parental cells. Remarkably, mitochondria, and thereby, mitochondrial DNA from the parental cells did not mix upon zygote formation, but remained segregated at the poles by attaching to clusters of the dynein anchor Mcp5 via its coiled-coil domain. We observed that this tethering of parental mitochondria to the poles results in uniparental inheritance of mitochondria, wherein two of the four spores formed subsequently contained mitochondria from one parent and the other spores, mitochondria from the other parent. Further, the presence of dynein on an Mcp5 cluster precluded the attachment of mitochondria to the same cluster. Taken together, we reveal a distinct mechanism that achieves uniparental inheritance by segregation of parental mitochondria.

cell biology↗

bioRxiv2017

Microtubule dynamics regulates mitochondrial fission

Mitochondria are organized as tubular networks in the cell and undergo fission and fusion. While several of the molecular players involved in mediating mitochondrial dynamics have been identified, the precise cellular cues that initiate fission or fusion remain largely unknown. In fission yeast, mitochondria are organized along microtubule bundles. Here, we employed deletions of kinesin-like proteins to perturb microtubule dynamics, and determined that cells with long microtubules exhibited long, but fewer mitochondria, whereas cells with short microtubules exhibited short, but several mitochondria due to reduced mitochondrial fission in the former and elevated fission in the latter. Correspondingly, upon onset of closed mitosis in fission yeast, wherein interphase microtubules assemble to form the spindle within the nucleus, we measured increased mitochondrial fission. We determined that the consequent rise in the mitochondrial copy number was necessary to reduce partitioning errors while stochastically partitioning mitochondria between daughter cells. We discovered that the association of mitochondria with microtubules physically impeded the assembly of the fission protein Dnm1 around mitochondria, resulting in inhibition of mitochondrial fission. Taken together, we demonstrate a novel mechanism for regulation of mitochondrial fission that is dictated by the interaction between mitochondria and the microtubule cytoskeleton.

cell biology↗