Filopodia numbers impact chemotactic migration speed.

Migrating cells sense and respond to external chemical and physical cues, enabling them to efficiently reach their destinations. Filopodia are slender actin-filled membrane protrusions implicated in interacting with the extracellular environment in many contexts, such as neuronal growth cone guidance and the capture of prey by immune cells and unicellular organisms. The role of filopodia in chemotactic guidance in fast-moving amoeboid cells has not been well-studied.

Modulation of Filopodial Myosin Function.

MyTH-FERM (MF) myosins are essential for filopodia formation in both Metazoa and Amoebozoa ( DdMyo7; mammalian Myo10) but their roles in filopodia formation are not fully understood. Taking advantage of a mutation in the highly conserved actin binding interface of another MF myosin, the () mutation of Myo15A that reduces its function, the impact of altering the myosin-F-actin interaction on filopodia formation was investigated. The mutation, a D to G substitution (Gong et al, 2022, Sci Adv), was introduced into DdMyo7 or Myo10 and filopodia formation assessed by quantitative analysis of number, length and myosin tip enrichment.

Reduced cell-substrate adhesion formation promotes cell migration in .

Many cells adhere to the extracellular matrix (ECM) for efficient cell migration. This adhesion is mediated by focal adhesions, a protein complex linking the ECM to the intracellular cytoskeleton. Focal adhesions have been studied extensively in metazoan mesenchymal cells, but recent research in physiological contexts and amoeboid cells suggests that focal adhesion regulation differs from the mesenchymal focal adhesion paradigm.

Myosin 2 drives actin contractility in fast-crawling species outside of the amorphean lineage.

Myosin 2-dependent actin contractility drives essential cell functions including fast crawling motility in animal cells, amoebae, and other species from the Amorphea lineage. Whether and how species outside this single eukaryotic group can generate contractile actin networks has been largely unexplored. We demonstrate that , an amoeba from the Heterolobosea-an evolutionarily distant eukaryotic lineage that includes the fastest known crawling eukaryotes-expresses three distinct Myosin 2 homologs.

The filopodial myosin DdMyo7 is a slow, calcium-regulated motor.

MyTH4-FERM (MF) myosins are a family of molecular motors with critical roles in the formation and organization of thin membrane protrusions supported by parallel bundles of actin - filopodia, microvilli, and stereocilia. The amoeboid MF myosin DdMyo7 is essential for filopodia formation but its mechanism of action is unknown. The motor properties of a forced-dimer of the DdMyo7 motor were characterized using an in vitro motility assay to address this question.

Reduced cell-substrate adhesion formation promotes cell migration in .

Many cells adhere to the extracellular matrix for efficient cell migration. This adhesion is mediated by focal adhesions, a protein complex linking the extracellular matrix to the intracellular cytoskeleton. Focal adhesions have been studied extensively in Metazoan mesenchymal cells, but recent research in physiological contexts and amoeboid cells suggest that focal adhesion regulation differs from the mesenchymal focal adhesion paradigm.

filoVision - using deep learning and tip markers to automate filopodia analysis.

Filopodia are slender, actin-filled membrane projections used by various cell types for environment exploration. Analyzing filopodia often involves visualizing them using actin, filopodia tip or membrane markers. Due to the diversity of cell types that extend filopodia, from amoeboid to mammalian, it can be challenging for some to find a reliable filopodia analysis workflow suited for their cell type and preferred visualization method.

The evolution and diversity of actin-dependent cell migration.

Many eukaryotic cells, including animal cells and unicellular amoebae, use dynamic-actin networks to crawl across solid surfaces. Recent discoveries of actin-dependent crawling in additional lineages have sparked interest in understanding how and when this type of motility evolved. Tracing the evolution of cell crawling requires understanding the molecular mechanisms underlying motility.

VASP-mediated actin dynamics activate and recruit a filopodia myosin.

Filopodia are thin, actin-based structures that cells use to interact with their environments. Filopodia initiation requires a suite of conserved proteins but the mechanism remains poorly understood. The actin polymerase VASP and a MyTH-FERM (MF) myosin, DdMyo7 in amoeba, are essential for filopodia initiation.

The many roles of myosins in filopodia, microvilli and stereocilia.

Filopodia, microvilli and stereocilia represent an important group of plasma membrane protrusions. These specialized projections are supported by parallel bundles of actin filaments and have critical roles in sensing the external environment, increasing cell surface area, and acting as mechanosensors. While actin-associated proteins are essential for actin-filament elongation and bundling in these protrusions, myosin motors have a surprising role in the formation and extension of filopodia and stereocilia and in the organization of microvilli.

The actin networks of chytrid fungi reveal evolutionary loss of cytoskeletal complexity in the fungal kingdom.

Cells from across the eukaryotic tree use actin polymer networks for a wide variety of functions, including endocytosis, cytokinesis, and cell migration. Despite this functional conservation, the actin cytoskeleton has undergone significant diversification, highlighted by the differences in the actin networks of mammalian cells and yeast. Chytrid fungi diverged before the emergence of the Dikarya (multicellular fungi and yeast) and therefore provide a unique opportunity to study actin cytoskeletal evolution.

Dictyostelium myosin 1F and myosin 1E inhibit actin waves in a lipid-binding-dependent and motor-independent manner.

Actin waves are F-actin-rich entities traveling on the ventral plasma membrane by the treadmilling mechanism. Actin waves were first discovered and are best characterized in Dictyostelium. Class I myosins are unconventional monomeric myosins that bind lipids through their tails.

Putting the brakes on a myosin motor.

Insulin-stimulated trafficking of GLUT4 requires the myosin motor Myo1C and signaling adaptor 14-3-3β. Originally, it was thought that 14-3-3β promotes GLUT4 transport by binding the Myo1C lever arm and activating the Myo1C motor. New work by Ji and Ostap using assays reveals that 14-3-3β binding actually inhibits Myo1C motility, prompting reconsideration of the functional relationship between 14-3-3β and Myo1C and the regulatory potential of atypical light chains.

Basic-hydrophobic sites are localized in conserved positions inside and outside of PH domains and affect localization of myosin 1s.

Myosin 1s have critical roles in linking membranes to the actin cytoskeleton via direct binding to acidic lipids. Lipid binding may occur through PIP3/PIP2-specific PH domains or nonspecific ionic interactions involving basic-hydrophobic (BH) sites but the mechanism of myosin 1s distinctive lipid targeting is poorly understood.  Now we show that PH domains occur in all myosin 1s and that the BH sites of Myo1A, B, C, D, and F are in conserved positions near the β3/β4 loops of their PH domains.

Optimized filopodia formation requires myosin tail domain cooperation.

Filopodia are actin-filled protrusions employed by cells to interact with their environment. Filopodia formation in Amoebozoa and Metazoa requires the phylogenetically diverse MyTH4-FERM (MF) myosins DdMyo7 and Myo10, respectively. While Myo10 is known to form antiparallel dimers, DdMyo7 lacks a coiled-coil domain in its proximal tail region, raising the question of how such divergent motors perform the same function.

Developing Evolutionary Cell Biology.

Recent advances in both phylogenetic comparisons and the development of experimentally tractable organisms, in the growing field of evolutionary cell biology, pave the way for gaining a molecular understanding of the development of multicellularity in the animal lineage.

Myosin-Driven Intracellular Transport.

The delivery of intracellular material within cells is crucial for maintaining normal function. Myosins transport a wide variety of cargo, ranging from vesicles to ribonuclear protein particles (RNPs), in plants, fungi, and metazoa. The properties of a given myosin transporter are adapted to move on different actin filament tracks, either on the disordered actin networks at the cell cortex or along highly organized actin bundles to distribute their cargo in a localized manner or move it across long distances in the cell.

Myosin 7 and its adaptors link cadherins to actin.

Cadherin linkages between adjacent stereocilia and microvilli are essential for mechanotransduction and maintaining their organization. They are anchored to actin through interaction of their cytoplasmic domains with related tripartite complexes consisting of a class VII myosin and adaptor proteins: Myo7a/SANS/Harmonin in stereocilia and Myo7b/ANKS4B/Harmonin in microvilli. Here, we determine high-resolution structures of Myo7a and Myo7b C-terminal MyTH4-FERM domain (MF2) and unveil how they recognize harmonin using a novel binding mode.

An evolutionary perspective on cell migration: Digging for the roots of amoeboid motility.

Fritz-Laylin et al. (2017. https://doi.

Growing, splitting and stacking myosin II filaments.

Spectacular images of the process of myosin II filament formation and organization in migrating cells are unveiled by super-resolution imaging. A combination of short- and long-range interactions with actin filaments is seen to play a critical role in filament partitioning and alignment into contractile actin arcs and stress fibres.

MyTH4-FERM myosins have an ancient and conserved role in filopod formation.

The formation of filopodia in Metazoa and Amoebozoa requires the activity of myosin 10 (Myo10) in mammalian cells and of Dictyostelium unconventional myosin 7 (DdMyo7) in the social amoeba Dictyostelium However, the exact roles of these MyTH4-FERM myosins (myosin tail homology 4-band 4.1, ezrin, radixin, moesin; MF) in the initiation and elongation of filopodia are not well defined and may reflect conserved functions among phylogenetically diverse MF myosins. Phylogenetic analysis of MF myosin domains suggests that a single ancestral MF myosin existed with a structure similar to DdMyo7, which has two MF domains, and that subsequent duplications in the metazoan lineage produced its functional homolog Myo10.

Coordinated recruitment of Spir actin nucleators and myosin V motors to Rab11 vesicle membranes.

There is growing evidence for a coupling of actin assembly and myosin motor activity in cells. However, mechanisms for recruitment of actin nucleators and motors on specific membrane compartments remain unclear. Here we report how Spir actin nucleators and myosin V motors coordinate their specific membrane recruitment.

Myosin MyTH4-FERM structures highlight important principles of convergent evolution.

Myosins containing MyTH4-FERM (myosin tail homology 4-band 4.1, ezrin, radixin, moesin, or MF) domains in their tails are found in a wide range of phylogenetically divergent organisms, such as humans and the social amoeba Dictyostelium (Dd). Interestingly, evolutionarily distant MF myosins have similar roles in the extension of actin-filled membrane protrusions such as filopodia and bind to microtubules (MT), suggesting that the core functions of these MF myosins have been highly conserved over evolution.

Selective localization of myosin-I proteins in macropinosomes and actin waves.

Class I myosins are widely expressed with roles in endocytosis and cell migration in a variety of cell types. Dictyostelium express multiple myosin Is, including three short-tailed (Myo1A, Myo1E, Myo1F) and three long-tailed (Myo1B, Myo1C, Myo1D). Here we report the molecular basis of the specific localizations of short-tailed Myo1A, Myo1E, and Myo1F compared to our previously determined localization of long-tailed Myo1B.

The association of myosin IB with actin waves in dictyostelium requires both the plasma membrane-binding site and actin-binding region in the myosin tail.

F-actin structures and their distribution are important determinants of the dynamic shapes and functions of eukaryotic cells. Actin waves are F-actin formations that move along the ventral cell membrane driven by actin polymerization. Dictyostelium myosin IB is associated with actin waves but its role in the wave is unknown.