Biology subjects

Guha, M.

Publications and source records attributed to Guha, M..

5 recordsLinked to original sources

bioRxiv2025

SPEF1 mediates assembly of the central pair microtubule complexes in cilia of Tetrahymena.

SPEF1 is a conserved protein that reinforces the seam of central microtubules within the distal segment of motile cilia. We show that in Tetrahymena, loss of SPEF1 destabilized the central pair throughout the cilium length, producing gaps in the microtubule lattice, loss of proximal microtubule portions, and loss of lateral projections. While both central microtubules were affected, C1 suffered more damage than C2 and the defects were already apparent during ciliary assembly. Tetrahymena cells lacking SPEF1 had fewer cilia, which contained an excessively dense ciliary matrix and abnormal densities on the doublet microtubules. Although SPEF1 loss visibly affected only the central microtubules, it localized to all stable microtubules in the cell, both ciliary and non-ciliary. Within cilia, SPEF1 was enriched near the distal tip, but was also present throughout the middle segment, where it was more concentrated along the central than the outer doublet microtubules. In live cilia, SPEF1 particles were mostly stationary and turned over slowly, some diffused but none moved by IFT. We propose that SPEF1 acts as a stabilizer of central microtubules in both the middle and distal segment and its activity contributes to central microtubule assembly.

cell biology↗

bioRxiv2025

Auditory Perception Induces Cortical and Thalamic Event-Related Desynchronization in the Mouse

Studies of human perception have shown early cortical signals for primary information encoding, and later signals for higher order processing. An important late signal is the cortical event-related desynchronization (ERD) in the alpha (8-12Hz) and beta (12-30Hz) frequency band, which has been linked to human perceptual awareness. Detailed mechanistic investigation of the ERD would be greatly facilitated by availability of a suitable animal model. We conducted local field potential recordings in the mouse frontal association cortex (FrA), thalamic intralaminar centrolateral nucleus (Cl), primary auditory cortex (A1), and primary visual cortex (V1) during two auditory tasks. Fully audible brief 50 ms stimuli with both tasks produced early broadband gamma (30-100Hz) frequency activity at 0-250ms, followed by a late cortical alpha/beta ERD 250 - 750 ms after stimulus onset. The ERD was statistically significant in FrA and A1, but not in V1. Interestingly, a significant ERD was also observed in thalamic Cl. The magnitude of the ERD at full stimulus intensity, and the slope of the relationship between stimulus intensity versus ERD magnitude, were both largest in FrA, and smaller in Cl and A1. Conversely, for early broadband gamma activity the magnitude at full intensity and slopes were largest in A1, smaller in Cl and smaller still in FrA. These findings suggest that mice, like humans, process perceptual signals in hierarchically organized corticothalamic networks, and strongly support mice as a promising platform for further investigation of the ERD to better understand the origin and function of this robust yet understudied electrophysiological phenomenon. Significance StatementAuditory-induced alpha/beta event-related desynchronizations (ERDs), decreases in cortical activity between 8 and 30Hz following auditory stimulus presentation, are thought to represent systems underlying higher perception and cognition. However, fundamental mechanistic studies are difficult in humans, the dominant organism for studying this phenomenon. In this study we assess mice as a potential alternative model organism. Our results demonstrate that mice exhibit auditory-induced alpha/beta ERDs, that this response is also present in subcortical regions of the mouse brain, and that the cortical ERD is largest and most strongly related to auditory stimulus amplitude in association cortex rather than in primary auditory cortex. These results support the efficacy of mice as an ideal model organism for further examination of alpha/beta ERDs.

neuroscience↗

bioRxiv2024

Gram-positive bacteria are primed for surviving lethal doses of antibiotics and chemical stress

Antibiotic resistance kills millions worldwide yearly. However, a major contributor to recurrent infections lies in a small fraction of bacterial cells, known as persisters. These cells are not inherently antibiotic-resistant, yet they lead to increased antibiotic usage, raising the risk of developing resistant progenies. In a bacterial population, individual cells exhibit considerable fluctuations in their gene expression levels despite being cultivated under identical, stable conditions. This variability in cell-to-cell characteristics (phenotypic diversity) within an isogenic population enables persister cells to withstand antibiotic exposure by entering a non-dividing state. We recently showed the existence of "primed cells" in E. coli. Primed cells are dividing cells prepared for antibiotic stress before encountering it and are more prone to form persisters. They also pass their "prepared state" down for several generations through epigenetic memory. Here, we show that primed cells are common among distant bacterial lineages, allowing for survival against antibiotics and other chemical stress, and form in different growth phases. They are also responsible for increased persister levels in transition and stationary phases compared to the log phase. We tested and showed that the Gram-positive bacterium Bacillus megaterium, evolutionarily very distant from E. coli, forms primed cells and has a transient epigenetic memory that is maintained for 7 generations or more. We showed this using ciprofloxacin and the non-antibiotic chemical stress fluoride. It is well established that persister levels are higher in the stationary phase than in the log phase, and B. megaterium persisters levels are nearly identical from the early to late-log phase but are [~]2-fold and [~]4-fold higher in the transition and stationary phase, respectively. It was previously proposed that there are two distinct types of persisters: Type II forms in the log phase, while Type I forms in the stationary phase. However, we show that primed cells lead to increased persisters in the transition and stationary phase and found no evidence of Type I or II persisters with distant phenotypes. Overall, we have provided substantial evidence of the importance of primed cells and their transitory epigenetic memories to surviving stress.

microbiology↗

bioRxiv2023

Farnesoid X receptor agonism prevents neutrophil extracellular traps via reduced sphingosine-1-phosphate in chronic kidney disease

BackgroundActivation of the farnesoid X receptor (FXR) reduces renal inflammation, but the underlying mechanisms remain elusive. Neutrophil extracellular traps (NETs) are webs of DNA formed when neutrophils undergo specialized programmed cell death (NETosis). Sphingosine-1-phosphate (S1P) is a signaling lipid that stimulates NETosis via its receptor on neutrophils. Here, we identify FXR as a negative regulator of kidney NETosis via repressing S1P signaling in male but not female mice. MethodsWe determined the effects of the FXR agonist obeticholic acid (OCA) in mouse models of adenosine phosphoribosyltransferase deficiency and Alport syndrome. We assessed renal NETosis by immunofluorescence in these models and in biopsies from patients with Alport syndrome (6 male, 9 female). We also inhibited de novo sphingosine production in Alport mice to show a causal relationship between S1P signaling and renal NETosis. ResultsRenal FXR activity is greatly reduced in both models, and OCA prevents kidney fibrosis, inflammation, and lipotoxicity. OCA reduces renal neutrophilic inflammation and NETosis in male adenine and Alport mice, but not in female adenine mice. Extensive NETosis was also identified in human Alport kidney biopsies. Kidney sphingosine kinase 1 (Sphk1) expression is increased in mice with kidney disease and reduced by OCA in male but not female mice. Also, Sphk1 expression correlates with NETosis in male but not female mice. Short-term inhibition of sphingosine synthesis reduces neutrophilic inflammation and NETosis. ConclusionFXR agonism represses kidney Sphk1 expression in male but not female mice. This inhibits renal S1P signaling, thereby reducing neutrophilic inflammation and NETosis in a sex-dependent manner.

pharmacology and toxicology↗

bioRxiv2019

Microtubule glycylation promotes basal body attachment to the cell cortex

Motile cilia generate directed hydrodynamic flow that is important for the motility of cells and extracellular fluids. To optimize directed hydrodynamic flow, motile cilia are organized and oriented into a polarized array. Basal bodies (BB) nucleate and position motile cilia at the cell cortex. Cytoplasmic BB-associated microtubules are conserved structures that extend from BBs. Using the ciliate, Tetrahymena thermophila, combined with EM-tomography and light microscopy, we show that BB-appendage microtubules assemble coincident with new BB assembly and are attached to the cell cortex. These BB-appendage microtubules are specifically marked with post translational modifications of tubulin, including glycylation. Mutations that prevent glycylation shorten BB-appendage microtubules and disrupt BB positioning and cortical attachment. Consistent with the attachment of BB-appendage microtubules to the cell cortex for BB positioning, mutations that disrupt the cellular cortical cytoskeleton similarly disrupt the cortical attachment and positioning of BBs. In summary, BB-appendage microtubules promote the organization of ciliary arrays through attachment to the cell cortex.\n\nSUMMARY STATEMENTBasal bodies position motile cilia at the cell cortex. This study finds tubulin glycylation to promote BB-associated microtubule elongation and structural attachment of basal bodies to the cells cortical cytoskeleton.

cell biology↗