Biology subjects

Papagiannakis, A.

Publications and source records attributed to Papagiannakis, A..

5 recordsLinked to original sources

bioRxiv2024

DNA/polysome phase separation and cell width confinement couple nucleoid segregation to cell growth in Escherichia coli

Chromosome segregation is essential for cellular proliferation. Unlike eukaryotes, bacteria lack cytoskeleton-based machinery to segregate their chromosomal DNA (nucleoid). The bacterial ParABS system segregates the duplicated chromosomal regions near the origin of replication. However, this function does not explain how bacterial cells partition the rest (bulk) of the chromosomal material. Furthermore, some bacteria, including Escherichia coli, lack a ParABS system. Yet, E. coli faithfully segregates nucleoids across various growth rates. Here, we provide theoretical and experimental evidence that polysome production during chromosomal gene expression helps compact, split, segregate, and position nucleoids in E. coli through out-of-equilibrium dynamics and polysome exclusion from the DNA meshwork, inherently coupling these processes to biomass growth across nutritional conditions. Halting chromosomal gene expression and thus polysome production immediately stops sister nucleoid migration while ensuing polysome depletion gradually reverses nucleoid segregation. Redirecting gene expression away from the chromosome and toward plasmids causes ectopic polysome accumulations that are sufficient to drive aberrant nucleoid dynamics. Cell width enlargement suggest that the proximity of the DNA to the membrane along the radial axis is important to limit the exchange of polysomes across DNA-free regions, ensuring nucleoid segregation along the cell length. Our findings suggest a self-organizing mechanism for coupling nucleoid segregation to cell growth.

microbiology↗

bioRxiv2024

Coupling of cell growth modulation to asymmetric division and cell cycle regulation in Caulobacter crescentus

In proliferating bacteria, growth rate is often assumed to be similar between daughter cells. However, most of our knowledge of cell growth derives from studies on symmetrically dividing bacteria. In many -proteobacteria, asymmetric division is a normal part of the life cycle, with each division producing daughter cells with different sizes and fates. Here, we demonstrate that the functionally distinct swarmer and stalked daughter cells produced by the model -proteobacterium Caulobacter crescentus have different average growth rates despite sharing an identical genome and environment. The discrepancy in growth rate is due to a growth slowdown during the cell cycle stage preceding DNA replication (the G1 phase), which is predominantly associated with swarmer cell functionality. We also provide evidence that the second messenger (p)ppGpp extends the timing of the G1/swarmer cell stage by slowing growth specifically during the beginning of the cell cycle. Our data further show that cells factor the amount and rate of their growth to control the G1/S transition, allowing them to adjust the time they spend with ecologically important G1-specific traits. Significance statementBacterial growth rate modulation is generally associated with changes in genetic make-up or environmental condition. This study demonstrates that the rate of cell growth can also vary between daughter cells and across cell cycle stages under invariant and unstressed environmental conditions. This is illustrated by the asymmetrically dividing -proteobacterium Caulobacter crescentus, which, at each division, produces two functionally distinct daughter cells that differ in average growth rate. This growth rate difference arises from a G1 phase-specific growth slowdown mediated, in part, by the (p)ppGpp alarmone. Altogether, this study showcases the coupling of cell growth modulation to asymmetric division and cell cycle regulation, which may have implications for other -proteobacteria given their cell cycle similarities with C. crescentus.

microbiology↗

bioRxiv2024

Genome concentration limits cell growth and modulates proteome composition in Escherichia coli

Defining the cellular factors that drive growth rate and proteome composition is essential for understanding and manipulating cellular systems. In bacteria, ribosome concentration is known to be a constraining factor of cell growth rate, while gene concentration is usually assumed not to be limiting. Here, using single-molecule tracking, quantitative single-cell microscopy, and modeling, we show that genome dilution in Escherichia coli cells arrested for DNA replication limits total RNA polymerase activity within physiological cell sizes across tested nutrient conditions. This rapid-onset limitation on bulk transcription results in sub-linear scaling of total active ribosomes with cell size and sub-exponential growth. Such downstream effects on bulk translation and cell growth are near-immediately detectable in a nutrient-rich medium, but delayed in nutrient-poor conditions, presumably due to cellular buffering activities. RNA sequencing and tandem-mass-tag mass spectrometry experiments further reveal that genome dilution remodels the relative abundance of mRNAs and proteins with cell size at a global level. Altogether, our findings indicate that chromosome concentration is a limiting factor of transcription and a global modulator of the transcriptome and proteome composition in E. coli. Experiments in Caulobacter crescentus and comparison with eukaryotic cell studies identify broadly conserved DNA concentration-dependent scaling principles of gene expression.

cell biology↗

bioRxiv2020

Proximity labeling at non-centrosomal microtubule-organizing centers reveals VAB-10B and WDR-62 as distinct microtubule regulators

Reorganization of microtubules from the centrosome to non-centrosomal subcellular sites is central to cell differentiation. To identify components of non-centrosomal microtubule organizing centers in differentiated cells of a living organism, we developed the biotin ligase-based proximity labeling approach TurboID for use in C. elegans. We identified proteins proximal to the non-centrosomal microtubule minus end protein PTRN-1/Patronin at the apical membrane of epithelial cells, focusing on two conserved proteins: spectraplakin protein VAB-10B and WDR-62, a protein we identify as homologous to vertebrate primary microcephaly disease gene WDR62. We found that WDR-62 and VAB-10B independently regulate the growth and localization of non-centrosomal microtubules and the apical targeting of microtubule minus end proteins. This regulation occurs downstream of cell polarity and in conjunction with actin. Our data suggest a division of labor where microtubule growth and anchoring are regulated by distinct complexes and uncover novel functions of spectraplakins and WDR62 family proteins.

cell biology↗

bioRxiv2018

Saccharomyces cerevisiae goes through distinct metabolic phases during its replicative lifespan

A comprehensive description of the phenotypic changes during cellular aging is key towards unraveling its causal forces. Using recently developed experimental tools, which previously had enabled us to map age related changes in proteome and transcriptome (Janssens et al., 2015), and model-based inference methods, here, we generated a comprehensive account of the metabolic changes during the entire replicative life of Saecharomyces cerevisiae. With age, we found decreasing metabolite levels, decreasing growth and substrate uptake rates accompanied by a switch from aerobic fermentation to a respiratory metabolism, with increased glycerol and acetate production. The identification of intracellular metabolic fluxes revealed an increase in redox cofactor turnover, likely to combat the increased production of reactive oxygen species. The identified metabolic changes possibly reflect a dynamic adaptation to the age-associated, non- homeostatic increase in volume. With metabolism being an important factor of the cellular phenotype, this work complements our recent mapping of the transcriptomic and proteomic changes towards a holistic description of the cellular processes during aging.

cell biology↗