Biology subjects

Maheshwari, R.

Publications and source records attributed to Maheshwari, R..

5 recordsLinked to original sources

bioRxiv2025

The centriculum, a membrane that surrounds C. elegans centrosomes, acts as a microtubule filter

Centrosomes are cytoplasmic microtubule-nucleating structures. They are considered membraneless organelles, but in several cell types they are surrounded by ER-derived membrane. In C. elegans early embryos, this membrane forms a dense membrane reticulum, named the centriculum, that affects centrosome structure and microtubule nucleating capacity. The centriculum is adjacent to the centrosomes pericentriolar material (PCM) and to abundant, short peri-centrosomal microtubules. Here we show that when microtubule abundance is reduced, centriculum and PCM size decrease, while the density of the PCM protein SPD-5 increases, suggesting that the PCM can be compacted. We further show that centriculum size is determined by microtubules, and that the centriculum likely limits the length of peri-centrosomal microtubules. Finally, we find that the centriculum is more porous where spindle microtubules pass compared to where astral microtubules pass. These data are consistent with the centriculum serving as a microtubule filter, blocking the extension of most, but not all, centrosome-nucleated microtubules. Finally, if microtubule-centriculum collisions result in microtubule catastrophe, the filter function of the centriculum could also explain the high concentration of soluble tubulin at the C. elegans centrosome. Summary StatementThe centriculum is a centrosome-associated membrane reticulum in C. elegans embryos. This study shows that its size depends on microtubules and that it may act as a filter, limiting microtubule growth.

cell biology↗

bioRxiv2025

Morpho-functional timeline of progressive cystic fibrosis pancreatic exocrine and endocrine pathology derived from semi-quantitative scoring and AI-driven quantitativeimage analysis

Cystic fibrosis (CF) is associated with pancreatic exocrine insufficiency (PEI) early in life and diabetes in up to 50% of adults. The underlying CF-related sequential changes within the pancreas associated with exocrine and endocrine insufficiency remain incompletely understood due to scarcity of available human tissue, protracted disease course and absence of established robust and reproducible analytical approaches. This study aimed to develop and apply a systematic analysis cross-sectionally to CF pancreatic tissue samples from donors over a wide age range to construct a timeline related to the main exocrine and endocrine changes underlying progressive disease. Based on a histopathological semi-quantitative scoring system and AI-driven quantitative image analysis pancreatic changes were individually evaluated and classified according to three patterns: fibrotic; fibrotic and lipotic; and lipoatrophic. This systematic evaluation was applied to 29 CF and 58 control donors without pancreatic disease. Rapid loss of acinar tissue with virtually complete absence by the age of 7 years was confirmed, mirrored by fatty tissue replacement - changes underlying PEI and likely preceding progression towards diabetes. Ductal blockage by thickened secretions was associated with increasing ductal dilatation accompanied by peri-ductal fibrosis, followed by ductal loss with involution of associated fibrosis in parallel with increasing adipocyte proportional area (PA). Remaining ducts were relatively small surrounded by residual fibrosis. Islets became increasingly clustered initially surrounded by activated pancreatic stellate cells (PSCs) and fibrosis and then disorganised by interposing fibrotic tissue between endocrine cell regions and surrounded by residual collagen stranding in a lipoatrophic pancreas. Overall islet mass was not significantly reduced but {beta}-cell PA was significantly reduced from birth without further loss over time. We concluded that the natural history of pancreatic CF progresses inexorably from peri-ductal fibrosis to global fat replacement with relatively well-maintained islet mass but PSC-associated fibrotic islet remodelling circumstantially implicated in {beta}-cell failure.

pathology↗

bioRxiv2024

Lipid Nanoparticle-Associated Inflammation is Triggered by Sensing of Endosomal Damage: Engineering Endosomal Escape without Side Effects

Lipid nanoparticles (LNPs) have emerged as the dominant platform for RNA delivery, based on their success in the COVID-19 vaccines and late-stage clinical studies in other indications. However, we and others have shown that LNPs induce severe inflammation, and massively aggravate pre-existing inflammation. Here, using structure-function screening of lipids and analyses of signaling pathways, we elucidate the mechanisms of LNP-associated inflammation and demonstrate solutions. We show that LNPs hallmark feature, endosomal escape, which is necessary for RNA expression, also directly triggers inflammation by causing endosomal membrane damage. Large, irreparable, endosomal holes are recognized by cytosolic proteins called galectins, which bind to sugars on the inner endosomal membrane and then regulate downstream inflammation. We find that inhibition of galectins abrogates LNP-associated inflammation, both in vitro and in vivo. We show that rapidly biodegradable ionizable lipids can preferentially create endosomal holes that are smaller in size and reparable by the endosomal sorting complex required for transport (ESCRT) pathway. Ionizable lipids producing such ESCRT-recruiting endosomal holes can produce high expression from cargo mRNA with minimal inflammation. Finally, we show that both routes to non-inflammatory LNPs, either galectin inhibition or ESCRT-recruiting ionizable lipids, are compatible with therapeutic mRNAs that ameliorate inflammation in disease models. LNPs without galectin inhibition or biodegradable ionizable lipids lead to severe exacerbation of inflammation in these models. In summary, endosomal escape induces endosomal membrane damage that can lead to inflammation. However, the inflammation can be controlled by inhibiting galectins (large hole detectors) or by using biodegradable lipids, which create smaller holes that are reparable by the ESCRT pathway. These strategies should lead to generally safer LNPs that can be used to treat inflammatory diseases.

bioengineering↗

bioRxiv2022

The Caenorhabditis elegans centrosome is surrounded by a membrane reticulum, the centriculum, that affects centrosome size and function

Centrosomes are membraneless organelles that nucleate microtubules. At their core is a pair of centrioles that recruit pericentriolar material (PCM), a phase-separated condensate. In many cell types, including human cells, centrosomes are surrounded by endoplasmic reticulum-derived membranes of unknown structure and function. Using volume electron microscopy, we show that the C. elegans centrosome is surrounded by a membrane reticulum that we call the centriculum, for centrosome-associated membrane reticulum. Increasing centriculum size by genetic means led to expansion of the PCM and increased microtubule nucleation capacity, an unexpected finding given that the PCM is a membraneless condensate. We provide evidence that the centriculum serves as a microtubule "filter" by limiting the number of microtubules that can elongate fully. We also show the centriculum fuses with the nuclear envelope during mitosis. We propose that this fusion contributes to nuclear envelope breakdown by transducing forces from the elongating spindle to the nuclear membranes.

cell biology↗

bioRxiv2021

An RNAi screen for genes that affect nuclear morphology in Caenorhabditis elegans reveals the involvement of unexpected processes

Aberration in nuclear morphology is one of the hallmarks of cellular transformation. However, the processes that, when mis-regulated, result aberrant nuclear morphology are poorly understood. In this study we carried out a systematic, high-throughput RNAi screen for genes that affect nuclear morphology in Caenorhabditis elegans embryos. The screen employed over 1700 RNAi constructs against genes required for embryonic viability. Nuclei of early embryos are typically spherical and their NPCs are evenly distributed. The screen was performed on early embryos expressing a fluorescently tagged component of the nuclear pore complex (NPC), allowing visualization of nuclear shape as well as the distribution of NPCs around the nuclear envelope. Our screen uncovered 182 genes whose down-regulation resulted in one or more abnormal nuclear phenotypes, including multiple nuclei, micronuclei, abnormal nuclear shape, anaphase bridges and abnormal NPC distribution. Many of these genes fall into common functional groups, including some that were not previously known to affect nuclear morphology, such as genes involved in mitochondrial function, the vacuolar ATPase and the CCT chaperonin complex. The results of this screen add to our growing knowledge of processes that affect nuclear morphology and that may be altered in cancer cells that exhibit abnormal nuclear shape.

cell biology↗