dictyNews Electronic Edition Volume 31, number 14 October 31, 2008 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. Upon publication of your paper, please send strains and plamids to  the Dicty Stock Center. For more information see  http://dictybase.org/StockCenter/Deposit.html. Back issues of dictyNews, the Dicty Reference database and other useful information is available at dictyBase - http://dictybase.org. ========= Abstracts ========= Clustering of VASP actively drives processive, WH2 domain-mediated actin  filament elongation Dennis Breitsprecher (1), Antje K Kiesewetter (1), Joern Linkner (1),  Claus Urbanke (1), Guenter P Resch (2,3), J Victor Small (2) and Jan Faix (1) 1) Institute for Biophysical Chemistry, Hannover Medical School, Hannover,  Germany 2) Institute of Molecular Biotechnology, Austrian Academy of Sciences,  Vienna, Austria 3) Research Institute of Molecular Pathology, Vienna, Austria EMBO J., in press Vasodilator-stimulated phosphoprotein (VASP) is a key regulator of dynamic  actin structures like filopodia and lamellipodia, but its precise function in  their formation is controversial. Using in vitro TIRF microscopy, we show for  the first time that both human and Dictyostelium VASP are directly involved  in accelerating filament elongation by delivering monomeric actin to the  growing barbed end. In solution, DdVASP markedly accelerated actin filament  elongation in a concentration-dependent manner but was inhibited by low  concentrations of capping protein (CP). In striking contrast, VASP clustered  on functionalized beads switched to processive filament elongation that  became insensitive even to very high concentrations of CP. Supplemented  with the in vivo analysis of VASP mutants and an EM structure of the protein,  we propose a mechanism by which membrane-associated VASP oligomers  use their WH2 domains to effect both the tethering of actin filaments and their  processive elongation in sites of active actin assembly. Submitted by: Jan Faix [faix@bpc.mh-hannover.de] -------------------------------------------------------------------------------- Segregate or cooperate- a study of the interaction between two species  of Dictyostelium Chandra N Jack, Julia G Ridgeway, Natasha J Mehdiabadi, Emily I Jones,  Tracy A Edwards, David C Queller and Joan E Strassmann  BMC Evolutionary Biology 2008, 8:293doi:10.1186/1471-2148-8-293 Background A major challenge for evolutionary biology is explaining altruism,  particularly when it involves death of one party and occurs across species.  Chimeric fruiting bodies of D. discoideum and D. purpureum develop from  formerly independent amoebae, and some die to help others. Here we  examine co-aggregation between D. discoideum and D. purpureum,  determine its frequency, which party benefits, and the extent of fair play  in contribution to the altruistic caste. Results We mixed cells from both species in equal proportions, and then we analyzed  193 individual fruiting bodies, which always had either a D. discoideum or  D. purpureum morphology (D. discoideum- 96, D. purpureum- 97). Fifty  percent of the fruiting bodies that looked like D. discoideum and 23% of  the fruiting bodies that looked like D. purpureum were chimeric, though  the majority of cells in any given fruiting body belonged to one species  (D. discoideum fruiting bodies- 0.72+/-0.05, D. purpureum fruiting bodies-  0.71+/-0.06). Clearly, there is species level recognition occurring that  keeps the cells mostly separate. The number of fruiting bodies with the  D. discoideum morphology was 486+/-61 in the mix treatment compared to  225+/- 32 fruiting bodies when D. discoideum was alone. However, the number  of D. discoideum spores did not significantly decrease from 2.75e7 +/-1.29e7  spores in the controls to 2.06e7 +/-8.33e6 spores in the mix treatments.  D. purpureum fruiting body and spore production decreased from 719+/- 111  fruiting bodies and 5.81e7+/-1.26e7 spores to 394+/-111 fruiting bodies  and 9.75e6 +/-2.25e6 spores in mixes compared to when it was grown alone. Conclusions Cooperating amoebae are able to make larger fruiting bodies, which is  advantageous for migration and dispersal. However, when both species are  present D. discoideum contributes more than its fair share to the spores  but both suffer a cost in producing fewer spores per fruiting body.  Submitted by: Chandra Jack [chanj@rice.edu] ============================================================== [End dictyNews, volume 31, number 14]