Evolution and mechanics of long jaws in butterflyfishes (family Chaetodontidae)

We analyzed the functional morphology and evolution of the long jaws found in several butterflyfishes. We used a conservative reanalysis of an existing morphological dataset to generate a phylogeny that guided our selection of seven short- and long-jawed taxa in which to investigate the functional anatomy of the head and jaws: Chaetodon xanthurus, Prognathodes falcifer (formerly Chaetodon falcifer), Chelmon rostratus, Heniochus acuminatus, Johnrandallia nigrirostris, Forcipiger flavissimus, and F. longirostris. We used manipulations of fresh, preserved, and cleared and stained specimens to develop mechanical diagrams of how the jaws might be protruded or depressed. Species differed based on the number of joints within the suspensorium. We used high-speed video analysis of five of the seven species (C. xanthurus, Chel. rostratus, H. acuminatus, F. flavissimus, and F. longirostris) to test our predictions based on the mechanical diagrams: two suspensorial joints should facilitate purely anteriorly directed protrusion of the lower jaw, one joint should allow less anterior protrusion and result in more depression of the lower jaw, and no joints in the suspensorium should constrain the lower jaw to simple ventral rotation around the jaw joint, as seen in generalized perciform fishes. We found that the longest-jawed species, F. longirostris, was able to protrude its jaws in a predominantly anterior direction and further than any other species. This was achieved with little input from cranial elevation, the principal input for other known lower jaw protruders, and is hypothesized to be facilitated by separate modifications to the sternohyoideus mechanism and to the adductor arcus palatini muscle. In F. longirostris the adductor arcus palatini muscle has fibers oriented anteroposteriorly rather than medial-laterally, as seen in most other perciforms and in the other butterflyfish studied. These fibers are oriented such that they could rotate the ventral portion of the quadrate anteriorly, thus projecting the lower jaw anteriorly. The intermediate species lack modification of the adductor arcus palatini and do not protrude their jaws as far (in the case of F. flavissimus) or in a purely anterior fashion (in the case of Chel. rostratus). The short-jawed species both exhibit only ventral rotation of the lower jaw, despite the fact that H. acuminatus is closely related to Forcipiger.     

Regulation of Protrusion Shape and Adhesion to the Substratum during Chemotactic Responses of Mammalian Carcinoma Cells

We report here the first direct observation of chemotaxis to EGF by rat mammary carcinoma cells. When exposed to a gradient of EGF diffusing from a micropipette, MTLn3 cells displayed typical ameboid chemotaxis, extending a lamellipod-like protrusion and moving toward the pipette. Using a homogeneous upshift in EGF to model stimulated lamellipod extension (J. E. Segallet al.,1996,Clin. Exp. Metastasis14, 61–72), we analyzed the relationship between adhesion and chemoattractant-stimulated protrusion. Exposure to EGF led to a rapid remodeling of the adhesive contacts on adherent cells, in synchrony with extension of a flat lamellipod over the substratum. EGF-stimulated lamellipods still extended in the presence of adhesion-blocking peptides or over nonadhesive surfaces. They were, however, slightly shorter and retracted rapidly under those conditions. The major protrusive structure observed on well-spread, adherent cells, after EGF stimulation was a flat broad lamellipod, whether or not in contact with the substratum, while cells in suspension showed transient protrusive activity over the entire cell surface. We conclude that the initial adhesive status of the cell conditions the shape of the outcoming protrusion. Altogether our results suggest that, although adhesive contacts are not necessary for lamellipod extension, they play a role in stabilizing the protrusion as well as in the control of its final shape and amplitude.     

The cell ratchet: Interplay between efficient protrusions and adhesion determines cell motion

Many physiological and pathological processes involve directed cell motion. In general, migrating cells are represented with a polarized morphology with extending and retracting protrusions at the leading edge. However, cell motion is a more complex phenomenon. Cells show heterogeneous morphologies and high protrusive dynamics is not always related to cell shape. This prevents the quantitative prediction of cell motion and the identification of cellular mechanisms setting directionality. Here we discuss the importance of protrusion fluctuations in directed cell motion. We show how their spatiotemporal distribution and dynamics determine the fluctuations and directions of cell motion for NIH3T3 fibroblasts plated on micro-patterned adhesive ratchets.¹ We introduce efficient protrusions and direction index which capture short-term cell motility over hours: these new read-outs allow the prediction of parameters characteristic for the long-term motion of cells over days. The results may have important implications for the study of biological phenomena where directed cell migration is involved, in morphogenesis and in cancer.     

HepG2.2.15 as a model for studying cell protrusion and migration regulated by S100 proteins

Much of the difficulty in elucidating the precise function of S100 protein family has been attributed to functional redundancy and compensation by its conserved family members. In this study, we showed that seven S100 family members were almost totally undetectable in HepG2.2.15 cells, while all of them were highly expressed in its parental HepG2 cells. Re-expression of S100 proteins in HepG2.2.15 cells can partially rescue their defects in cell protrusion and migration through the regulation of cytoskeletons and adhesions. Thus, HepG2.2.15 can serve as a useful model for studying cell protrusion and migration regulated by S100 proteins.     

How tropomyosin regulates lamellipodial actin‐based motility: a combined biochemical and reconstituted motility approach

At the leading edge of migrating cells, protrusive forces are developed by the assembly of actin filaments organised in a lamellipodial dendritic array at the front and a more distal lamellar linear array. Whether these two arrays are distinct or functionally linked and how they contribute to cell migration is an open issue. Tropomyosin severely inhibits lamellipodium formation and facilitates the lamellar array while enhancing migration, by a mechanism that is not understood. Here we show that the complex in vivo effects of tropomyosin are recapitulated in the reconstituted propulsion of neural Wiskott–Aldrich syndrome protein (N‐WASP)‐functionalised beads, which is based on the sole formation of a dendritic array of actin‐related protein (Arp)2/3‐branched filaments. Actin‐depolymerising factor (ADF) and tropomyosin control the length of the actin tail. By competing with Arp2/3 during filament branching, tropomyosin displays opposite effects on propulsion depending on the surface density of N‐WASP. Tropomyosin binding to the dendritic array is facilitated following filament debranching, causing its enrichment at the rear of the actin tail, like in vivo. These results unveil the mechanism by which tropomyosin generates two morphologically and dynamically segregated actin networks from a single one.     

BACE1 modulates filopodia-like protrusions induced by sodium channel beta4 subunit

Processing of APP by BACE1 plays a crucial role in the pathogenesis of Alzheimer disease (AD). Recently, the voltage-gated sodium channel (Na_v) β4 subunit (β4), an auxiliary subunit of Na_v that is supposed to serve as a cell adhesion molecule, has been identified as a substrate for BACE1. However, the biological consequence of BACE1 processing of β4 remains illusive. Here, we report the biological effects of β4 processing by BACE1. Overexpression of β4 in Neuro2a cells promoted neurite extension and increased the number of F-actin rich filopodia-like protrusions. While coexpression of BACE1 together with β4 further accelerated neurite extension, the number of filopodia-like protrusions was reduced. Overexpression of C-terminal fragment of β4 that was generated by BACE1 (β4-CTF) partially recapitulated the results obtained with BACE1 overexpression. These results suggest that the processing of β4 by BACE1 regulates neurite length and filopodia-like protrusion density in neurons.     

Identification and characterization of a novel neural cell adhesion molecule (NCAM)-associated protein from quail myoblasts: relationship to myotube formation and induction of neurite-like protrusions

Abstract We identified a novel neural cell adhesion molecule (NCAM)-associated protein, myo genesis-related and N CAM- a ssociated p rotein (MYONAP), the expression of which increases during the formation of myotubes in quail myoblasts transformed with a temperature-sensitive mutant of Rous sarcoma virus (QM-RSV cells). MYONAP shares homology with PL48 in human cytotrophoblasts and KIAA0386 in human brain. Excess expression of MYONAP in presumptive QM-RSV myoblasts induced long protrusions like neurites in cooperation with microtubules. Suppression of MYONAP by antisense cDNA prevented myotubes from forming in spite of the expression of myogenin, creatine kinase, and myosin, and rendered myoblast membranes resistant to fusion. Yeast two-hybrid screening showed that MYONAP interacted with NCAM specifically. Deletion of the NCAM-associated domain resulted in a loss of the function that induces neurite-like protrusions to form and disturbed the elongation of microtubules. The results suggested that MYONAP influenced the functions of microtubules and was involved in the formation of myotubes via its interaction with NCAM.     

Adhesion tunes speed and persistence by coordinating protrusions and extracellular matrix remodeling

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Allosteric transcription stimulation by RNA polymerase II super elongation complex

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Both actin and polyproline interactions of profilin-1 are required for migration, invasion and capillary morphogenesis of vascular endothelial cells

The objective of the present study was to evaluate how different ligand interactions of profilin-1 (Pfn1), an actin-binding protein that is upregulated during capillary morphogenesis of vascular endothelial cells (VEC), contribute to migration and capillary forming ability of VEC. We adopted a knockdown-knockin experimental system to stably express either fully functional form or mutants of Pfn1 that are impaired in binding to two of its major ligands, actin (H119E mutant) and proteins containing polyproline domains (H133S mutant), in a human dermal microvascular cell line (HmVEC) against near-null endogenous Pfn1 background. We found that silencing endogenous Pfn1 expression in HmVEC leads to slower random migration, reduced velocity of membrane protrusion and a significant impairment in matrigel-induced cord formation. Only re-expression of fully functional but not any of the two ligand-binding deficient mutants of Pfn1 rescues the above defects. We further show that loss of Pfn1 expression in VEC inhibits three-dimensional capillary morphogenesis, MMP2 secretion and ECM invasion. VEC invasion through ECM is also inhibited when actin and polyproline interactions of Pfn1 are disrupted. Together, these experimental data demonstrate that Pfn1 regulates VEC migration, invasion and capillary morphogenesis through its interaction with both actin and proline-rich ligands.