dictyNews Electronic Edition Volume 26, number 4 January 27, 2006 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. ============= Abstracts ============= A retinoblastoma orthologue controls stalk/spore preference in Dictyostelium Harry MacWilliams (1) Kimchi Doquang (1,2) Roberto Pedrola (3) Gytha Dollman (1) Daniela Grassi (3) Thomas Peis (1) Adrian Tsang(2) and Adriano Ceccarelli (3) (1) Biozentrum der Ludwig-Maximilians-UniversitŠt, Planegg-Martinsried, Germany (2) Centre for Structural and Functional Genomics, Concordia University, Montreal, Quebec, Canada (3) Dipartimento di Scienze Cliniche e Biologiche, Universitˆ di Torino, Ospedale S.Luigi, Torino, Italy Development, in press We describe rblA, the Dictyostelium ortholog of the retinoblastoma susceptibility gene Rb. In the growth phase, rblA expression is correlated with several factors which lead to ÒpreferenceÓ for the spore pathway. During multicellular development, expression increases 200-fold in differentiating spores. RblA-null strains differentiate stalk cells and spores normally, but in chimeras with wild-type the mutant shows a strong preference for the stalk pathway. RblA-null cells are hypersensitive to the stalk morphogen DIF, suggesting that rblA normally suppresses the DIF response in cells destined for the spore pathway. RblA overexpression during growth leads to G1 arrest, but since growing Dictyostelium are overwhelmingly G2, rblA does not seem to be important in the normal cell cycle. RblA-null cells show reduced cell size and a premature growth-development transition; the latter appears anomalous but may reflect selection pressures acting on social ameba. Submitted by: Harry MacWilliams [macw@zi.biologie.uni-muenchen.de] ----------------------------------------------------------------------------- Single-molecule analysis of chemoattractant-stimulated membrane recruitment of a PH domain-containing protein Satomi Matsuoka(1), Miho Iijima(2), Tomonobu M. Watanabe(1), Hidekazu Kuwayama(1), Toshio Yanagida(1), Peter N. Devreotes(2) and Masahiro Ueda(1) (1)Laboratories for Nanobiology, Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan (2)Department of Cell Biology, Johns Hopkins University School of Medicine 725 N. Wolfe St., 114 WBSB, Baltimore, Maryland, 21205, USA Journal of Cell Science, in press Molecular mechanisms of chemotactic response are highly conserved among many eukaryotic cells including human leukocytes and Dictyostelium cells. The cells can sense the differences in chemoattractant concentration across the cell body and respond by extending pseudopods from the cell side facing to a higher concentration. Pseudopod formation is regulated by binding of pleckstrin homology-domain-containing proteins to phosphatidylinositol 3,4,5-trisphosphates localized at the leading edge of chemotaxing cells. However, molecular mechanisms underlying dynamic features of a pseudopod have not been fully explained by the known properties of pleckstrin homology-domain-containing proteins. To investigate the mechanisms, we visualized single molecules of green fluorescent protein tagged to Crac, a pleckstrin homology-domain-containing protein in Dictyostelium discoideum cells. Whereas populations of Crac molecules exhibited a stable steady-state localization at pseudopods, individual molecules bound transiently to phosphatidylinositol 3,4,5-trisphosphates for ~120 milliseconds, indicating dynamic properties of pleckstrin homology-domain-containing protein. Receptor stimulation did not alter the binding stability but regulated the number of bound pleckstrin homology-domain molecules via phosphatidylinositol 3,4,5-trisphosphates metabolisms. These results demonstrate that the steady-state localization of pleckstrin homology-domain-containing proteins at the leading edge of chemotaxing cells is dynamically maintained by rapid recycling of individual pleckstrin homology-domain-containing proteins. The short interaction between pleckstrin homology-domain and phosphatidylinositol 3,4,5-trisphosphates contributes to accurate and sensitive chemotactic movements through the dynamic redistributions. These dynamic properties might be general for signaling components involved in chemotaxis. Submitted by: Satomi Matsuoka [matsuoka@phys1.med.osaka-u.ac.jp] ----------------------------------------------------------------------------- Identification of Novel Centrosomal Proteins in Dictyostelium discoideum by Comparative Proteomic Approaches Yvonne Reinders, Irene Schulz,  Ralph Graf,  and Albert Sickmann* Protein Mass Spectrometry and Functional Proteomics Group, Rudolf-Virchow-Center for ExperimentalBiomedicine, Julius-Maximilians-University Wuerzburg, Versbacher Strasse 9, 97078 Wuerzburg, Germany Journal of Proteome Research, in press The centrosome functions as the main microtubule-organization center of the cell and is of importance for all microtubule-dependent processes such as organelle transport and directionality of cell migration. One of the major model organisms in centrosome research is the slime mold Dictyostelium discoideum. Since only 10 centrosomal proteins are known so far in Dictyostelium discoideum, the elucidation of new centrosomal components may give a more comprehensive understanding of centrosomal function. To distinguish between centrosomal and contaminating proteins we established different separation and relative quantification strategies including techniques such as iTRAQ and DIGE. In this work, we present the identification of several known components as well as more than 70 new candidatess currently subject of further investigationssfor the protein inventory of the Dictyostelium centrosome. Among these protein identifications, 44% represent hypothetical proteins of still unknown function associated with the centrosome. Submitted by: Ralph Graef [r.graef@zeiss.de] ============================================================================== [End dictyNews, volume 26, number 4]