Global cell sorting is mediated by local cell–cell interactions in the C. elegans embryo

AbstractThe Caenorhabditis elegans embryo achieves pattern formation by sorting cells into coherent regions before morphogenesis is initiated. The sorting of cells is coupled to their fate. Cells move extensively relative to each other to reach their correct position in the body plan. Analyzing the mechanism of cell sorting in in vitro culture experiments using 4D microscopy, we show that all AB-derived cells sort only according to their local neighbors, and that all cells are able to communicate with each other. The directions of cell movement do not depend on a cellular polarity but only on local cell–cell interactions; in experimental situations, this allows even the reversal of the polarity of whole regions of the embryo. The work defines a new mechanism of pattern formation we call “cell focusing”

N=2 Worldsheet Instantons Yield Cubic Self-Dual Yang-Mills

When the gauge instantons on the N=2 string worldsheet are properly included in the sum over topologies, the breaking of SO(2,2) Lorentz symmetry in R^{2,2} is parametrized by a spacetime twistor containing the string coupling and theta angle. The resulting (tree-level) effective action for the open string is not Yang's but Leznov's cubic action for self-dual Yang-Mills in a light-cone gauge. In the closed case, Plebanski's action for self-dual gravity gets modified analogously. In contrast to the N=1 NSR string, picture-changing is not locally invertible, but produces a semi-infinite tower of massless physical states with ever-increasing spin, perhaps related to harmonic superspace. A truncation yields the two-field action of Chalmers and Siegel.Comment: 9 pages, no figures, LaTeX (amsbsy,latexsym

String-induced Yang-Mills coupling to self-dual gravity

By considering N=2 string amplitudes we determine the (2+2)-dimensional target space action for the physical degrees of freedom: self-dual gravity and self-dual Yang-Mills, together with their respective infinite towers of higher-spin inequivalent picture states. Novel `stringy' couplings amongst these fields are essential ingredients of an action principle for the effective target space field theory. We discuss the covariant description of this theory in terms of self-dual fields on a hyperspace parametrised by the target space coordinate and a commuting chiral spinor.Comment: 20 pages, no figure

An anti-biofilm cyclic peptide targets a secreted aminopeptidase from P. aeruginosa

Funding: CMC and CJH are funded by the Wellcome Trust (210486/Z/18/Z), additional funding was provided by the University of St Andrews Impact Innovation Fund. MB (Bergkessel) is funded by the University of Dundee/Wellcome Trust Institutional Strategic Support Fund [204816/Z/16/Z] and UKRI Future Leaders Fellowship (funded by the Medical Research Council) [MR/T041811/1].Pseudomonas aeruginosa is an opportunistic pathogen that causes serious illness, especially in immunocompromised individuals. P. aeruginosa forms biofilms that contribute to growth and persistence in a wide range of environments. Here we investigated the aminopeptidase, P. aeruginosa aminopeptidase (PaAP) from P. aeruginosa, which is highly abundant in the biofilm matrix. PaAP is associated with biofilm development and contributes to nutrient recycling. We confirmed that post-translational processing was required for activation and PaAP is a promiscuous aminopeptidase acting on unstructured regions of peptides and proteins. Crystal structures of wild-type enzymes and variants revealed the mechanism of autoinhibition, whereby the C-terminal propeptide locks the protease-associated domain and the catalytic peptidase domain into a self-inhibited conformation. Inspired by this, we designed a highly potent small cyclic-peptide inhibitor that recapitulates the deleterious phenotype observed with a PaAP deletion variant in biofilm assays and present a path toward targeting secreted proteins in a biofilm context.Publisher PDFPeer reviewe

D-Brane Scattering of N=2 Strings

The amplitudes for emission and scattering of N=2 strings off D-branes are calculated. We consider in detail the amplitudes and for the different types of D-branes. For some D-branes we find massive poles in the scattering spectrum that are absent in the ordinary N=2 spectrum.Comment: 10 pages, LaTe

Extended Self-Dual Yang-Mills from the N=2 String

We show that the physical degrees of freedom of the critical open string with N=2 superconformal symmetry on the worldsheet are described by a self-dual Yang-Mills field on a hyperspace parametrised by the coordinates of the target space R^{2,2} together with a commuting chiral spinor. A prepotential for the self-dual connection in the hyperspace generates the infinite tower of physical fields corresponding to the inequivalent pictures or spinor ghost vacua of this string. An action is presented for this tower, which describes consistent interactions amongst fields of arbitrarily high spin. An interesting truncation to a theory of five fields is seen to have no graphs of two or more loops.Comment: 19 pages; typos corrected, note and reference added; published versio

The conserved transmembrane proteoglycan Perdido/Kon-tiki is essential for myofibrillogenesis and sarcomeric structure in Drosophila

This is an Open Access article distributed under the terms of the Creative Commons Attribution License.Muscle differentiation requires the assembly of high-order structures called myofibrils, composed of sarcomeres. Even though themolecular organization of sarcomeres is well known, the mechanisms underlying myofibrillogenesis are poorly understood. It has been proposed that integrin-dependent adhesion nucleates myofibrils at the periphery of the muscle cell to sustain sarcomere assembly. Here, we report a role for the gene perdido (perd, also known as kon-tiki, a transmembrane chondroitin proteoglycan) in myofibrillogenesis. Expression of perd RNAi in muscles, prior to adult myogenesis, can induce misorientation and detachment of Drosophila adult abdominal muscles. In comparison to controls, perd-depleted muscles contain fewer myofibrils, which are localized at the cell periphery. These myofibrils are detached from each other and display a defective sarcomeric structure. Our results demonstrate that the extracellular matrix receptor Perd has a specific role in the assembly of myofibrils and in sarcomeric organization. We suggest that Perd acts downstream or in parallel to integrins to enable the connection of nascent myofibrils to the Z-bands. Our work identifies the Drosophila adult abdominalmuscles as amodel to investigate in vivo the mechanisms behind myofibrillogenesis.Research was funded by the Spanish Ministry of Science and Innovation [grant number BFU2011-26745]. B.E. was funded in part by the Ramon y Cajal program by the Universidad Pablo de Olavide; J.J.P.-M. was funded by the Proyecto de Excelencia of Junta de Andalucía; M.B. was funded by a Wellcome Trust Senior Investigator Award to Peter Lawrence [grant number WT096645MA]. M.D.M.-B. is funded by the Consejo Superior de Investigaciones Científicas.Peer Reviewe

The conserved transmembrane proteoglycan Perdido/Kon-tiki is essential for myofibrillogenesis and sarcomeric structure in Drosophila.

Muscle differentiation requires the assembly of high-order structures called myofibrils, composed of sarcomeres. Even though the molecular organization of sarcomeres is well known, the mechanisms underlying myofibrillogenesis are poorly understood. It has been proposed that integrin-dependent adhesion nucleates myofibrils at the periphery of the muscle cell to sustain sarcomere assembly. Here, we report a role for the gene perdido (perd, also known as kon-tiki, a transmembrane chondroitin proteoglycan) in myofibrillogenesis. Expression of perd RNAi in muscles, prior to adult myogenesis, can induce misorientation and detachment of Drosophila adult abdominal muscles. In comparison to controls, perd-depleted muscles contain fewer myofibrils, which are localized at the cell periphery. These myofibrils are detached from each other and display a defective sarcomeric structure. Our results demonstrate that the extracellular matrix receptor Perd has a specific role in the assembly of myofibrils and in sarcomeric organization. We suggest that Perd acts downstream or in parallel to integrins to enable the connection of nascent myofibrils to the Z-bands. Our work identifies the Drosophila adult abdominal muscles as a model to investigate in vivo the mechanisms behind myofibrillogenesis

Mixed (open/closed) N=(2,2) string theory as an integrable deformation of self-duality

The exact effective field equations of motion, corresponding to the perturbative mixed theory of open and closed (2,2) world-sheet supersymmetric strings, are investigated. It is shown that they are only integrable in the case of an abelian gauge group. The gravitational equations are then stationary with respect to the Born-Infeld-type effective action.Comment: 9 pages, LaTe

Self-Dual Supergravity from N=2 Strings

A new heterotic N=2 string with manifest target space supersymmetry is constructed by combining a conventional N=2 string in the right-moving sector and a Green-Schwarz-Berkovits type string in the left-moving sector. The corresponding sigma model is then obtained by turning on background fields for the massless excitations. We compute the beta functions and we partially check the OPE's of the superconformal algebra perturbatively in $\alpha'$, all in superspace. The resulting field equations describe N=1 self-dual supergravity.Comment: 32 pages, Latex, discussion in pages 10, 11 revised so that it is compatible with the complex structure chosen in Appendix A. Appendix A slightly expanded. Final versio