dictyNews Electronic Edition Volume 35, number 19 Dec 23, 2010 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to dicty@northwestern.edu or by using the form at http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit. Back issues of dictyNews, the Dicty Reference database and other useful information is available at dictyBase - http://dictybase.org. Follow dictyBase on twitter: http://twitter.com/dictybase HAPPY HOLIDAYS AND A JOYOUS NEW YEAR! ========= Abstracts ========= Social selection and the evolution of cooperative groups: The example of the cellular slime moulds Vidyanand Nanjundiah (1, 2) and Santosh Sathe (2) (1) Department of Molecular Reproduction, Development and Genetics and (2) Centre for Ecological Sciences, Indian Institute of Science, Bangalore 560012, India (email: vidya@ces.iisc.ernet.in) Integrative Biology, accepted as a ÒPerspectiveÓ article Social selection can operate when the phenotype of an individual depends on its own genotype as well as on the phenotypes, and so genotypes, of other individuals. In such a situation one can associate a phenotype with a genotype only with reference to a specified social context. Phenotypic heterogeneity within groups can lead to social selection, and can do so even when all individuals are of the same genotype. For that to happen, phenotypic plasticity, namely the ability of a genotype to exhibit different phenotypes, is a prerequisite. However, co-operative social behaviour with division of labour demands that individuals of different phenotypes interact appropriately, not that they belong to the same genotype or have overlapping genetic interests. Interacting phenotypes, rather than shared genes, are the essential requirement for group life. A possible route to the evolution of social groups involves the following steps: (a) individuals that happen to be in spatial proximity benefit simply by virtue of their number; (b) traits that are already present act as preadaptations and improve the efficiency of the group; and (c) new adaptations evolve by social selection Ð that is, via interactions between individuals Ð and further strengthen group behaviour. Under natural conditions cellular slime mould amoebae form multicellular groups that can be genetically homogeneous (clonal) or heterogeneous (polyclonal). In either case the development of the group is broadly the same and displays strong cooperation between cells. A survey of cellular slime mould behaviour throws up numerous examples of social selection and supports the route sketched above for the evolution of social groups. The resulting perspective offers insights into multicellular development, both normal and abnormal. Submitted by Vidyanand Nanjundiah [vidya@ces.iisc.ernet.in] -------------------------------------------------------------------------------- Curvature recognition and force generation in phagocytosis Margaret Clarke1, Ulrike Engel2, Jennifer Giorgione1, Annette MŸller-Taubenberger3, Jana Prassler4, Douwe Veltman5, and GŸnther Gerisch4X 1 Program in Genetic Models of Disease, Oklahoma Medical Research Foundation, Oklahoma City, OK 73121, USA 2 Nikon Imaging Center at the University of Heidelberg, Bioquant, 69120 Heidelberg, Germany 3 Institut fŸr Zellbiologie, Ludwig-Maximilians-UniversitŠt MŸnchen, 80336 MŸnchen, Germany 4 Max-Planck-Institut fŸr Biochemie, 82152 Martinsried, Germany BMC Biology, in press Background The uptake of particles by actin-powered invagination of the plasma membrane is common to protozoa and to phagocytes involved in the immune response of higher organisms. The question addressed here is how a phagocyte may use geometrical cues to optimize force generation for the uptake of a particle. We survey mechanisms that enable a phagocyte to remodel actin organization in response to particles of complex shape. Results Using particles that consist of two lobes separated by a neck, we show that Dictyostelium cells transmit signals concerning the curvature of a surface to the actin system underlying the plasma membrane. Force applied to a concave region can divide a particle in two, allowing engulfment of the portion first encountered. The phagosome membrane bent around the concave region is marked by a protein containing an I-BAR domain in combination with an SH3 domain, similar to mammalian insulin receptor tyrosine kinase substrate p53 (IRSp53). Regulatory proteins enable the phagocyte to switch activities within seconds in response to particle shape. Ras, an inducer of actin polymerization, is activated along the cup surface. Coronin, which limits the lifetime of actin structures, is reversibly recruited to the cup, reflecting a program of actin depolymerization. Myosin-IÕs are candidate motor proteins for force generation in particle uptake, whereas myosin-II is engaged only in retracting a phagocytic cup after a switch to particle release. Thus, the constriction of a phagocytic cup differs from the contraction of a cleavage furrow in mitosis. Conclusions Phagocytes scan a particle surface for convex and concave regions. By modulating the spatio-temporal pattern of actin organization, they are capable of switching between different modes of interaction with a particle: either arresting at a concave region and applying force in an attempt to sever the particle there, or extending the cup along the particle surface to identify the very end of the object to be ingested. Our data illustrate the flexibility of regulatory mechanisms that are at a phagocyteÕs disposal in exploring an environment of irregular geometry. Submitted by: GŸnther Gerisch [gerisch@biochem.mpg.de] -------------------------------------------------------------------------------- Characterisation of the Dictyostelium homolog of chromatin binding protein DET1 suggests a conserved pathway regulating cell type specification and developmental plasticity Manu J. Dubin#, Sonja Kasten and Wolfgang Nellen* Department of Genetics, Kassel University, Heinrich-Plett-Str. 40, 34132 Kassel, Germany # Current address: Gregor Mendel Instiute, Dr.-Bohr-Gasse 3, 1030 Vienna, Austria *Author for correspondence: Prof. Dr. Wolfgang Nellen Eukaryotic Cell, in press DET1 (De-etiolated 1) is a chromatin binding protein involved in developmental regulation in both plants and animals. DET1 is largely restricted to multicellular eukaryotes and here we report the characterisation of a DET1 homolog from the social amoeba Dictyostelium discoideum. As in other species Dictyostelium DET1 is nuclear localised. In contrast to other species where it is an essential protein, loss of DET1 is non-lethal in Dictyostelium, although viability is significantly reduced. The phenotype of the det1- mutant is highly pleiotropic and results in a large degree of heterogeneity in developmental parameters. Loss of DET1 results in delayed and abnormal development with enlarged aggregation territories. Mutant slugs displayed cell type patterning with a bias towards the pre-stalk pathway. A number of DET1 interacting proteins are conserved in Dictyostelium and the apparently conserved role of DET1 in regulatory pathways involving the bZIP transcription factors DimB/c-Jun/HY5 suggests a highly conserved mechanism regulating development in multicellular eukaryotes. While the mechanism by which DET1 functions is unclear, it appears that it has a key role in regulation of developmental plasticity and integrating information on environmental conditions into the developmental program of an organism. Submitted by: Wolfgang Nellen [nellen@uni-kassel.de] ============================================================== [End dictyNews, volume 35, number 19]