Dicty News Electronic Edition Volume 25, number 3 August 5, 2005 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 Dicty-News, the Dicty Reference database and other useful information is available at dictyBase - http://dictybase.org. ============= Abstracts ============= Social behaviour in genetically heterogeneous groups of Dictyostelium giganteum Sonia Kaushik, Bandhana Katoch and Vidyanand Nanjundiah Indian Institute of Science Bangalore Behavioural Ecology & Sociobiology, in press The Dictyostelid or cellular slime moulds (CSMs) are soil amoebae with an asexual life cycle involving social behaviour and division of labour. The most obvious distinction is between 'germ line'â or pre-spore cells, that survive, and 'somatic'â or pre-stalk cells, that eventually die. A plausible hypothesis to explain the apparent altruism of pre-stalk cells is that it is directed at clonal relatives. We have tested this hypothesis by comparing indices of altruistic behaviour between clonal and chimaeric (genetically heterogeneous) social groups. The groups were generated by mixing amoebae belonging to distinguishable strains of Dictyostelium giganteum .The amoebae of one strain do not aggregate at all when mixed with any of three other strains and aggregate poorly with a fourth. Among the latter, co-aggregation occurs but is followed by varying extents of sorting-out. At times two strains form separate fruiting bodies; in other cases they remain together but are clustered in clonal groups within a single chimaeric structure. Our expectation was that the allocation of cells to the stalk pathway would be higher, and to the spore pathway lower, in clonal social groups than in chimaeras. The expectation was not always fulfilled. Also, three strains could be arrayed in a linear rank-order in terms of the relative efficiencies of spore-formation in binary mixtures, but when all three were mixed they were equally efficient. More than overall genetic similarity, cell fate in a chimaera seems to result from complex non-linear interactions based on epigenetic differences. Submitted by: Vidyanand Nanjundiah [vidya@ces.iisc.ernet.in] ----------------------------------------------------------------------------- Prespore cell fate bias in G1 phase of the cell cycle in Dictyostelium Guokai Chen and Adam Kuspa Verna and Marrs McLean Department of Biochemistry and Molecular Biology, and Department of Molecular and Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston TX 77030. Eukaryotic Cell, in press By generating a population of Dictyostelium cells that are in the G1 phase of the cell cycle we have examined the influence of cell cycle status on cell fate specification, cell-type proportioning and its regulation and terminal differentiation. We exploited the fact that spores encapsulate in G1 to produce populations of G1-phase cells by germinating spores and harvesting the emergent amoebae before they re-entered the cell cycle. The lack of observable mitosis during the development of these cells and the quantification of their cellular DNA content suggests that they remain in G1 throughout development. Furthermore, chromosomal DNA synthesis was not detectable these cells, indicating that no S phase had occurred, although substantial mtDNA synthesis did occur in prespore cells. The G1-phase cells underwent normal morphological development and sporulation, but displayed an elevated prespore/prestalk ratio of 5.7 compared to the 3.0 ratio normally observed in populations dominated by G2-phase cells. When migrating slugs produced by G1-phase cells were bisected, each half could re-establish the 5.7 prespore/prestalk ratio. These results demonstrate that Dictyostelium cells can carryout the entire developmental cycle in G1 phase of the cell cycle, and that passage from G2 into G1 phase is not required for sporulation. Our results also suggest that the population asymmetry provided by the distribution of cells around the cell cycle at the time of starvation is not strictly required for cell-type proportioning. Finally, when developed together with G2-phase cells, G1-phase cells preferentially become prespore cells and exclude G2-phase cells from the prespore/spore cell population, suggesting that G1-phase cells have an advantage over G2-phase cells in executing the spore cell differentiation pathway. Submitted by: Adam Kuspa [akuspa@bcm.tmc.edu] ============================================================================== [End Dicty News, volume 25, number 3]