Biology subjects

Anjum, S.

Publications and source records attributed to Anjum, S..

4 recordsLinked to original sources

bioRxiv2024

The TissueTractor, a device for applying large strains to tissues and cells for simultaneous high-resolution live cell microscopy.

Mechanical strain substantially influences tissue shape and function in various contexts, from embryonic development to disease progression. Disruptions in these processes can result in congenital abnormalities and short-circuit mechanotransduction pathways. Manipulating strain in live tissues is crucial for understanding its impact on cellular and subcellular activities. Existing tools, such as optogenetic modulation of strain, are limited to small strain over limited distance and durations. Here, we introduce a high-strain stretcher system, the TissueTractor, designed for high-resolution spatiotemporal imaging of live tissues, enabling strain application varying from 0% to over 150%. This system is needed to unravel the intricate connections between mechanical forces and developmental processes. We demonstrated the stretcher with Xenopus laevis organotypic explants, human umbilical endothelial cells, and mouse neonatal cardiomyocytes to highlight the stretchers adaptability. These demonstrations underscore the potential of this stretcher to deepen our understanding of the mechanical cues governing tissue dynamics and morphogenesis. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=170 SRC="FIGDIR/small/600827v3_ufig1.gif" ALT="Figure 1"> View larger version (46K): org.highwire.dtl.DTLVardef@207163org.highwire.dtl.DTLVardef@1f424e7org.highwire.dtl.DTLVardef@1a2e9e1org.highwire.dtl.DTLVardef@a8d785_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2023

Assessing mechanical agency during apical apoptotic cell extrusion

Epithelial tissues maintain homeostasis through the continual addition and removal of cells. Homeostasis is necessary for epithelia to maintain barrier function and prevent the accumulation of defective cells. Unfit, excess, and dying cells can be removed from epithelia by the process of extrusion. Controlled cell death and extrusion in the epithelium of the larval zebrafish tail fin coincides with oscillation of cell area, both in the extruding cell and its neighbors. Both cell-autonomous and non-autonomous factors have been proposed to contribute to extrusion but have been challenging to test by experimental approaches. Here we develop a dynamic cell-based biophysical model that recapitulates the process of oscillatory cell extrusion to test and compare the relative contributions of these factors. Our model incorporates the mechanical properties of individual epithelial cells in a two-dimensional simulation as repelling active particles. The area of cells destined to extrude oscillates with varying durations or amplitudes, decreasing their mechanical contribution to the epithelium and surrendering their space to surrounding cells. Quantitative variations in cell shape and size during extrusion are visualized by a hybrid weighted Voronoi tessellation technique that renders individual cell mechanical properties directly into an epithelial sheet. To explore the role of autonomous and non-autonomous mechanics, we vary the biophysical properties and behaviors of extruding cells and neighbors such as the period and amplitude of repulsive forces, cell density, and tissue viscosity. Our data suggest that cell autonomous processes are major contributors to the dynamics of extrusion, with the mechanical microenvironment providing a less pronounced contribution. Our computational model based on in vivo data serves as a tool to provide insights into the cellular dynamics and localized changes in mechanics that promote elimination of unwanted cells from epithelia during homeostatic tissue maintenance.

biophysics↗

bioRxiv2023

N-terminal targeting sequences and coding sequences act in concert to determine the localization and trafficking pathway of apicoplast proteins in Toxoplasma gondii.

Toxoplasma gondii has a relict plastid, the apicoplast, to which proteins are targeted after synthesis in the cytosol. Proteins exclusively found in the apicoplast use a Golgi-independent route for trafficking, while dually targeted proteins found in both the apicoplast and the mitochondrion use a Golgi-dependent route. For apicoplast targeting, N-terminal signal sequences have been shown to direct the localization of different reporters. In this study, we use chimeric proteins to dissect out the roles of N-terminal sequences and coding sequences in apicoplast localization and the choice of the trafficking route. We show that when the N-termini of a dually targeted protein, TgTPx1/2, or of an apicoplast protein, TgACP, are fused with the reporter protein, enhanced Green Fluorescent Protein (eGFP) or endogenous proteins, TgSOD2, TgSOD3, TgACP or TgTPx1/2, the chimeric proteins exhibit flexibility in apicoplast targeting depending on the coding sequences. Further, the chimeras that are localized to the apicoplast use different trafficking pathways depending on the combination of the N-terminal signals and the coding sequences. This report shows, for the first time, that in addition to the N-terminal signal sequences, targeting and trafficking signals also reside within the coding sequences of apicoplast proteins.

molecular biology↗

bioRxiv2023

Wat1/mLst8, a TOR complex protein regulates mitochondrial integrity and calcium ion homeostasis in fission yeast S. pombe

The mTOR complexes play a fundamental role in mitochondrial biogenesis and cellular homeostasis. Wat1, an ortholog of mammalian Lst8 is an important component of TOR complex and is essential for the regulation of downstream signaling. Earlier we reported the role of Wat1 in oxidative stress response. Here, we show that the inactivation of wat1 leads to respiratory defects and mitochondrial depolarization leading to decrease in ATP production. The confocal and electron microscopy in wat1{Delta} cells revealed the fragmented mitochondrial morphology implying its role in mitochondrial fission. Furthermore, we also showed its role in autophagy and the maintenance of calcium ion homeostasis. Additionally, tor2-287 mutant cells also exhibit defects in mitochondrial integrity indicating the TORC1-dependent involvement of Wat1 in the maintenance of mitochondrial homeostasis. The interaction studies of Wat1 and Tor2 with Por1 and Mmm1 proteins revealed a cross-talk between mitochondria and endoplasmic reticulum through the Mitochondria-associated membranes (MAM) and endoplasmic reticulum-mitochondria encounter structure (ERMES) complex, involving TORC1. Taken together, this study demonstrates involvement of Wat1/mLst8 in harmonizing various mitochondrial functions, redox status, and Ca2+ homeostasis.

cell biology↗