Biology subjects

Krendel, M.

Publications and source records attributed to Krendel, M..

11 recordsLinked to original sources

bioRxiv2026

Disease-associated amino acid substitutions outside canonical motor motifs impair Myo1e localization and activity

Steroid-resistant nephrotic syndrome (SRNS) is a severe kidney disorder characterized by proteinuria and disruption of glomerular filtration, often driven by genetic defects in genes encoding proteins required for podocyte functions. Among these, MYO1E, encoding the actin- and membrane-associated motor protein Myosin 1e (Myo1e), has been implicated in familial and sporadic forms of SRNS. Here, we investigated two MYO1E missense variants, A92E and G562R, identified in trans in a patient with childhood-onset SRNS and located outside canonical P-loop and switch subdomains of the Myo1e motor domain. Both residues are highly conserved, located within predicted -helices in the motor domain, and replaced by larger charged residues, which may reduce protein stability or folding. In podocyte-derived cells, both mutants failed to localize at intercellular junctions and displayed reduced colocalization with actin. The G562R variant additionally formed cytoplasmic aggregates that were partially expression-level-dependent and exhibited decreased fluorescence recovery after photobleaching, indicating impaired protein dynamics. In vitro motility and ATPase assays indicated that the G562R mutant exhibited a marked loss of ATPase activity while the A92E mutant displayed ATPase activity similar to the WT but was characterized by reduced motility and thermal stability. Together, these results demonstrate that A92E and G562R mutations compromise Myo1e localization and function, supporting their pathogenic role in SRNS.

cell biology↗

bioRxiv2026

Semi-automated reconstruction of glomerular architecture from 3D confocal microscopy data

Nephrons are the functional units of the kidney; within each nephron, the glomerulus is the initial site of selective filtration that allows removal of waste products while preserving proteins in the bloodstream. Each glomerulus consists of a network of capillaries surrounded by specialized epithelial cells, podocytes, which mediate selective filtration. Abnormalities in glomerular structure impair renal function, resulting in proteinuria and kidney disease. Although several microscopy-based approaches exist to characterize glomerular architecture and structural abnormalities, quantitative analysis is often limited by labor-intensive image segmentation. In this study we present a semi-automated approach for segmentation and analysis of glomerular architecture from three-dimensional confocal microscopy data. Using mTmG transgenic mice that express membrane-associated EGFP in podocytes and membrane-associated tdTomato across all other cell types, we reconstruct podocyte processes and glomerular capillaries from volumetric renal images. This semi-automated approach reduces manual segmentation effort and supports more efficient, standardized analysis of glomerular architecture in three-dimensional confocal microscopy datasets.

cell biology↗

bioRxiv2026

Myo1e/f regulate phagocytic podosomes to promote efficient cup closure in macrophages

Phagocytosis requires coordinated remodeling of the actin cytoskeleton to generate protrusive and contractile forces that drive target engulfment. Class I myosins Myo1e and Myo1f (Myo1e/f) have been implicated in linking the plasma membrane to the actin network, but their specific roles during Fc-receptor-mediated phagocytosis remain unclear. Using CRISPR-edited RAW 264.7 macrophages lacking Myo1e and Myo1f, we show that double knockout (dKO) cells exhibit markedly reduced uptake of IgG-coated beads, a phenotype that is partially rescued by re-expression of either myosin. Lattice-light-sheet and confocal imaging revealed distinct F-actin architectures corresponding to the various stages of cup progression, including basal podosome-like adhesions, individual phagocytic podosomes (actin teeth) along the rim of the cup, and a contractile phagocytic ring formed by the reorganization of podosomes into a higher-order network. In Myo1e/f- deficient cells, podosome formation was diminished, actin teeth were largely absent, and the phagocytic ring formed prematurely, which was often accompanied by stalled cup progression and repeated engulfment attempts. Myo1e/f localized both to podosomes and to the inner surface of the phagocytic ring, non-muscle myosin II (NM2) localized to the outer surface, and the absence of Myo1e/f correlated with the diffuse distribution of NM2. In addition, Myo1e/f-deficient macrophages exhibited increased trogocytosis of antibody-opsonized HL-60 cells, indicating a shift from whole-target engulfment toward partial target ingestion. These results suggest that Myo1e/f coordinate spatial and temporal transitions between protrusive and contractile actin networks, thereby ensuring efficient phagocytic cup progression. Our findings highlight a dual role for Myo1e/f in adhesion regulation and force balance during macrophage phagocytosis.

cell biology↗

bioRxiv2025

Myo1e/f at the podosome base regulate podosome dynamics and promote macrophage migration

Cells of the monocyte lineage form specialized membrane-associated, actin-rich structures, called podosomes. Podosomes play important roles in cell adhesion and migration as well as the proteolytic degradation of the extracellular matrix. While podosomes are always closely associated with the plasma membrane, the structural components linking the podosome core, composed of branched actin, to the membrane are not fully understood. In this study we show that class I myosins, Myo1e and Myo1f, localize to a specific region of podosomes, underneath the podosome core and near the ventral plasma membrane, and that this localization is mainly mediated by the Myo1e/f TH2 domains. Respective knockdowns or knockouts of Myo1e/f lead to increased podosome size, altered turnover and lateral mobility, which is likely due to Myo1e/f regulating the attachment of core actin filaments to the plasma membrane. In addition, Myo1e/f double knockout macrophages were characterized by a reduction in 3D and 2D migration, even though these cells exhibited increased ability to degrade the extracellular matrix. Along with the other membrane-associated podosome components, such as the transmembrane proteins MT-MMP and CD44, and the GPI-anchored DNase X, Myo1e and Myo1f mark the membrane-proximal region of podosomes. We propose to label this region as the podosome "base", an additional substructure joining the current trifecta of the podosome cap, core, and ring.

cell biology↗

bioRxiv2022

Loss of Myosin-1e biases MMTV-PyMT induced breast cancer towards a 4 differentiated and secretory state

Expression of the unconventional myosin, Myosin-1e (Myo1e), has been shown to contribute to tumor progression in the MMTV-PyMT mouse model of mammary tumorigenesis and is associated with poor outcome in breast cancer patients. However, the specific effects of Myo1e expression on the mammary tumor cells remain unidentified. Here, we used Myo1e-KO and wild-type (WT) MMTV-PyMT mice on a pure genetic background to further investigate the molecular and cellular effects of Myo1e expression. Myo1e-WT tumors were characterized by an increased abundance of intra-epithelial macrophages and lower amounts of the extracellular matrix. Transcriptomic profiling of WT and Myo1e-KO tumors identified a pattern of differential expression of tumor suppressor and tumor-promoting genes that was consistent with the observed differences in tumor progression and morphology between the genotypes, and also revealed differential expression of genes associated with secretion and cell-cell adhesion. In agreement with the RNA-seq findings, Myo1e-expressing tumor cells exhibited increased proliferation and elevated nuclear enrichment of YAP1 transcriptional activator compared to Myo1e-KO tumor cells. To investigate tumor cell-autonomous effects of Myo1e expression, we used the epithelial cell line PY-230 derived from the MMTV-PyMT-induced mouse tumor to create Myo1e-depleted cells by Crispr-mediated genome editing. Cells deficient in Myo1e had increased expression of genes encoding milk components compared to the wild-type cells. Electric cell-substrate impedance sensing (ECIS) measurements showed that depletion of Myo1e in PY-230 cells resulted in increased resistance to electrical current indicating enhanced epithelial barrier function. Overall, we find that Myo1e expression biases tumors towards a less-differentiated, pro-tumorigenic state, and that depletion of Myo1e is associated with a pro-secretory, more differentiated state.

cancer biology↗

bioRxiv2022

Myo1e knockout in the adult podocytes leads to proteinuria but has less severe consequences for kidney function than Myo1e loss during renal development

Myosin 1e (Myo1e) is expressed in specialized epithelial cells in the kidney (podocytes) and plays an important role in renal filtration. Knockout of Myo1e in mice and mutations in the MYO1E gene in humans cause proteinuria and disrupt the ultrastructure of glomeruli, the initial segments of renal nephrons that are responsible for selective excretion of waste products without the loss of proteins from the bloodstream. Previous studies have demonstrated that the loss of Myo1e early in development results in severe defects in renal function in mice and may lead to end-stage renal disease in patients homozygous for MYO1E mutations. However, little is known about the effects of Myo1e loss later in life. In this study, we used inducible knockout of Myo1e in mouse podocytes to examine the effects of Myo1e loss from the adult kidneys. We have found that Myo1e loss after the completion of renal development causes proteinuria and podocyte defects but the effects are milder and more variable compared to the effects of Myo1e knockout in developing podocytes. These findings indicate that Myo1e plays an important role in podocyte development and differentiation but may also contribute to the maintenance of the glomerular barrier in the adult kidneys.

cell biology↗

bioRxiv2022

Theoretical model of efficient phagocytosis driven by curved membrane proteins and active cytoskeleton forces

Phagocytosis is the process of engulfment and internalization of comparatively large particles by the cell, that plays a central role in the functioning of our immune system. We study the process of phagocytosis by considering a simplified coarse grained model of a three-dimensional vesicle, having uniform adhesion interaction with a rigid particle, in the presence of curved membrane proteins and active cytoskeletal forces. Complete engulfment is achieved when the bending energy cost of the vesicle is balanced by the gain in the adhesion energy. The presence of curved (convex) proteins reduces the bending energy cost by self-organizing with higher density at the highly curved leading edge of the engulfing membrane, which forms the circular rim of the phagocytic cup that wraps around the particle. This allows the engulfment to occur at much smaller adhesion strength. When the curved proteins exert outwards protrusive forces, representing actin polymerization, at the leading edge, we find that engulfment is achieved more quickly and at lower protein density. We consider spherical as well as non-spherical particles, and find that non-spherical particles are more difficult to engulf in comparison to the spherical particles of the same surface area. For non-spherical particles, the engulfment time crucially depends upon the initial orientation of the particles with respect to the vesicle. Our model offers a mechanism for the spontaneous self-organization of the actin cytoskeleton at the phagocytic cup, in good agreement with recent high-resolution experimental observations. Significance StatementPhagocytosis is an important process that plays a central role in our immune system, and also during nutrient uptake, drug delivery and pathogen invasion. Despite its biological importance, it is still not understood how the actin cytoskeleton is coordinated spatio-temporally during the phagocytosis process. We present a simple model that explains the dynamics and self-organization of the membrane and the actin cytoskeleton during the engulfment process, based on curved membrane activators of actin polymerization.

biophysics↗

bioRxiv2021

Steroid-resistant nephrotic syndrome associated MYO1E mutations have differential effects on myosin 1e localization, dynamics, and activity

Myo1e is a non-muscle motor protein enriched in the podocyte foot processes. Mutations in MYO1E are associated with steroid-resistant nephrotic syndrome (SRNS). Here, we set out to differentiate between the pathogenic and neutral MYO1E variants identified in SRNS patients by exome sequencing. Based on protein sequence conservation and structural predictions, two mutations in the motor domain, T119I and D388H, were selected for this study. EGFP-tagged Myo1e constructs were delivered into the Myo1e-KO podocytes via adenoviral infection to analyze Myo1e protein stability, Myo1e localization, and clathrin-dependent endocytosis, which is known to involve Myo1e activity. Furthermore, truncated Myo1e constructs were expressed using the baculoviral expression system and used to measure Myo1e ATPase and motor activity in vitro. Both mutants were expressed as full-length proteins in the Myo1e-KO podocytes. However, unlike wild-type (WT) Myo1e, the T119I variant was not enriched at the cell junctions or clathrin-coated vesicles (CCVs) in podocytes. In contrast, the D388H variant localization was similar to the WT. Surprisingly, the dissociation of the D388H variant from cell-cell junctions and CCVs was decreased, suggesting that this mutation also affects Myo1e activity. The ATPase activity and the ability to translocate actin filaments were drastically reduced for the D388H mutant, supporting the findings from cell-based experiments. The experimental pipeline developed in this study allowed us to determine that the T119I and D388H mutations appear to be pathogenic and gain additional knowledge in the Myo1e role in podocytes. This workflow can be applied to the future characterization of novel MYO1E variants associated with SRNS.

cell biology↗

bioRxiv2021

Phagocytic 'teeth' and myosin-II 'jaw' power target constriction during phagocytosis

Phagocytosis requires rapid actin reorganization and spatially controlled force generation to ingest targets ranging from pathogens to apoptotic cells. How actomyosin activity directs membrane extensions to engulf such diverse targets remains unclear. Here, we combine lattice light-sheet microscopy (LLSM) with microparticle traction force microscopy (MP-TFM) to quantify actin dynamics and subcellular forces during macrophage phagocytosis. We show that spatially localized forces leading to target constriction are prominent during phagocytosis of antibody-opsonized targets. This constriction is largely mediated by Arp2/3-mediated assembly of discrete actin protrusions containing myosin 1e and 1f ("teeth") that are interconnected in a ring-like organization. Contractile myosin-II activity contributes to late-stage phagocytic force generation and progression, suggesting a specific role in phagocytic cup closure. Observations of partial target eating attempts and sudden target release via a popping mechanism suggest that constriction may be critical for resolving complex in vivo target encounters. Overall, our findings suggest a phagocytic cup-shaping mechanism that is distinct from cytoskeletal remodeling in 2D cell motility and may contribute to mechanosensing and phagocytic plasticity.

cell biology↗

bioRxiv2019

Human Myosin 1e tail but not motor domain replaces fission yeast Myo1 domains to support myosin-I function during endocytosis

In both unicellular and multicellular organisms, long-tailed class I myosins function in clathrin-mediated endocytosis. Myosin 1e (Myo1e) in vertebrates and Myo1 in fission yeast have similar domain organization, yet whether these proteins or their individual protein domains are functionally interchangeable remains unknown. In an effort to assess functional conservation of class I myosins, we tested whether human Myo1e could replace Myo1 in fission yeast Schizosaccharomyces pombe and found that it was unable to substitute for yeast Myo1. To determine if any individual protein domain is responsible for the inability of Myo1e to function in yeast, we created human-yeast myosin-I chimeras. By functionally testing these chimeric myosins in vivo, we concluded that the Myo1e motor domain is unable to function in yeast, even when combined with the yeast Myo1 tail and a full complement of yeast regulatory light chains. Conversely, the Myo1e tail, when attached to the yeast Myo1 motor domain, supports localization to actin patches and partially rescues the endocytosis defect in myo1{Delta} cells. Further dissection showed that both the TH1 and TH2-SH3 domains in the human Myo1e tail are required for localization and function of chimeric myosin-I at endocytic sites. Overall, this study provides insights into the role of individual myosin-I domains, expands the utility of fission yeast as a simple model system to study the effects of disease-associated MYO1E mutations, and supports a model of co-evolution between a myosin motor and its actin track.

cell biology↗

bioRxiv2018

Membrane-cytoskeleton mechanical feedback mediated by myosin-I controls phagocytic efficiency

Phagocytosis of invading pathogens or cellular debris requires a dramatic change in cell shape driven by actin polymerization. For antibody-covered targets, phagocytosis is thought to proceed through the sequential engagement of Fc-receptors on the phagocyte with antibodies on the target surface, leading to the extension and closure of the phagocytic cup around the target. We have found that two actin-dependent molecular motors, class 1 myosins myosin 1e and myosin 1f, are specifically localized to Fc-receptor adhesions and required for efficient phagocytosis of antibody-opsonized targets. Using primary macrophages lacking both myosin 1e and myosin 1f, we found that without the actin-membrane linkage mediated by these myosins, the organization of individual adhesions is compromised, leading to excessive actin polymerization, slower adhesion turnover, and deficient phagocytic internalization. This work identifies a novel role for class 1 myosins in coordinated adhesion turnover during phagocytosis and supports a model for a membrane-tension based feedback mechanism for phagocytic cup closure.\n\nO_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY

cell biology↗