Biology subjects

Ehrlicher, A. J.

Publications and source records attributed to Ehrlicher, A. J..

5 recordsLinked to original sources

bioRxiv2023

Integrin-like adhesin CglD confers traction and stabilizes bacterial focal adhesions involved in myxobacterial gliding motility

AO_SCPLOWBSTRACTC_SCPLOWIntegrins are crucial for eukaryotic cell attachment and motility within the extracellular matrix (ECM) via focal-adhesion formation, with their evolutionary emergence important for the development of multicellularity. Intriguingly, single gliding cells of the predatory deltaproteobacterium Myxococcus xanthus form bacterial focal-adhesion (bFA) sites; therein, helically-trafficked motors become immobilized at anchored locations through Glt apparatus association with cell-surface integrin I-domain-like adhesin CglB. Using traction-force, bead-force, and total internal reflection-fluorescence microscopies combined with biochemical approaches, we herein identify the von Willebrand A domain-containing cell-surface lipoprotein CglD to be a {beta}-integrin-like outer-membrane lipoprotein that functionally associates with and anchors the trans-envelope Glt-CglB gliding apparatus, stabilizing and efficiently anchoring this assembly at bFAs. Calcium dependence governs CglD importance, consistent with its integrated ECM eukaryotic cartilage oligomeric matrix protein domains. CglD thus confers mechanosensory and mechanotransductory capabilities to the gliding apparatus, helping explain bFA-mediated trans-envelope force transduction, from inner-membrane-embedded motors to the cell surface.

microbiology↗

bioRxiv2023

Tissue tension permits β-catenin phosphorylation to drive mesoderm specification in human embryonic stem cells.

The role of morphogenetic forces in cell fate specification is an area of intense interest. Our prior studies suggested that the development of high cell-cell tension in human embryonic stem cells (hESC) colonies permits the Src-mediated phosphorylation of junctional {beta}-catenin that accelerates its release to potentiate Wnt-dependent signaling critical for initiating mesoderm specification. Using an ectopically expressed nonphosphorylatable mutant of {beta}-catenin (Y654F), we now provide direct evidence that impeding tension-dependent Src-mediated {beta}-catenin phosphorylation impedes the expression of Brachyury (T) and the epithelial-to-mesenchymal transition (EMT) necessary for mesoderm specification. Addition of exogenous Wnt3a or inhibiting GSK3{beta} activity rescued mesoderm expression, emphasizing the importance of force dependent Wnt signaling in regulating mechanomorphogenesis. Our work provides a framework for understanding tension-dependent {beta}-catenin/Wnt signaling in the self-organization of tissues during developmental processes including gastrulation.

developmental biology↗

bioRxiv2019

Dynamic crosslinking of the actin cytoskeleton governs cell mechanics

Cells precisely control their mechanical properties to organize and differentiate into tissues. The architecture and connectivity of cytoskeletal filaments changes in response to mechanical and biochemical cues, allowing the cell to rapidly tune its mechanics from highly-crosslinked, elastic networks to weakly-crosslinked viscous networks. While the role of actin crosslinking in controlling actin network mechanics is well-characterized in purified actin networks, its mechanical role in the cytoplasm of living cells remains unknown. Here, we probe the frequency-dependent intracellular viscoelastic properties of living cells using multifrequency excitation and in situ optical trap calibration. At long timescales in the intracellular environment, we observe that the cytoskeleton becomes fluid-like. The mechanics are well-captured by a model in which actin filaments are dynamically connected by a single dominant crosslinker. A disease-causing point mutation (K255E) of the actin crosslinker -actinin 4 (ACTN4) causes its binding kinetics to be insensitive to tension. Under normal conditions, the viscoelastic properties of wild type (WT) and K255E+/- cells are similar. However, when tension is reduced through myosin II inhibition, WT cells relax 3x faster to the fluid-like regime while K255E+/- cells are not affected. These results indicate that dynamic actin crosslinking enables the cytoplasm to flow at long timescales.

biophysics↗

bioRxiv2019

Spatial distribution of lamin A determines nuclear stiffness and stress-mediated deformation

The nucleus is the largest organelle and information center of the cell; while diverse cellular components have been identified as mechanotransduction elements, the deformation of the nucleus itself is emerging as a critical mechanosensory mechanism, suggesting that the nuclear stiffness is essential in determining responses to intracellular and extracellular stresses. The nuclear membrane protein, lamin A, is known to be a dominant component in nuclear stiffening; however, the quantitative relationship between lamin A expression and nuclear deformation is still unclear. Here we measure the nuclear moduli as a function of lamin A expression and applied stress, revealing a linear dependence of bulk modulus on lamin A expression. We also find that the bulk modulus is anisotropic, with the vertical axis of the nucleus being more compliant than the minor and major axis. To examine how lamin A influences nuclear mechanics at the sub-micron scale we correlated the spatial distribution of lamin A with 3D nuclear envelope deformation, revealing that local areas of the nuclear envelope with higher expression levels of lamin A have correspondingly lower local deformations, and that increased lamin A expression levels result in a narrower distribution of smaller deformations. These findings describe the complex dispersion of nuclear deformations as a function of lamin A expression and distribution and implicate a role in mechanotransduction.

bioengineering↗

bioRxiv2017

Endocytosis caused by liquid-liquid phase separation of proteins

Membrane invagination and vesicle formation are key steps in endocytosis and cellular trafficking. Here, we show that endocytic coat proteins with prion-like domains (PLDs) form hemispherical puncta in the budding yeast, S. cerevisiae. These puncta have the hallmarks of biomolecular condensates and enable membrane remodeling to drive actin-independent endocytosis. The puncta, which we refer to as endocytic condensates, form and dissolve reversibly in response to changes in temperature and solution conditions. The condensates are organized around dynamic protein-protein interaction networks, which involve interactions among PLDs with high glutamine contents. The endocytic coat protein Sla1 is at the hub of the protein-protein interaction network. Using active rheology, we indirectly characterized the material properties of endocytic condensates. These experiments show that endocytic condensates are viscoelastic materials and allow us to estimate the interfacial tension between endocytic condensates and their surroundings. We then adapt the physics of contact mechanics, specifically the contact theory of Hertz, to develop a quantitative framework for describing how interfacial tensions among condensates, the membrane, and the cytosol can deform the plasma membrane to enable actin independent endocytosis.

cell biology↗