Dicty News Electronic Edition Volume 24, number 8 March 25, 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 ============= Temporal and Spatial Regulation of Phosphoinositide Signaling Mediates Cytokinesis Chris Janetopoulos, Jane Borleis, Francisca Vazquez, Miho Iijima, and Peter Devreotes Department of Cell Biology, Johns Hopkins University School of Medicine Dev Cell, in press Polarity is a prominent feature of both cell division and migration. While a key role for PI(3,4,5)P3 has been established for migration, phosphoinositide signaling during cytokinesis has not been reported. In chemotaxis, local accumulation of PI(3,4,5)P3 at the cellās leading edge, achieved through temporal and spatial regulation of PI3-kinases and the tumor suppressor, PTEN, biases the actin cytoskeleton and thereby controls directional sensing and polarity. We find that as migrating D. discoideum cells round up to enter cytokinesis, PI(3,4,5)P3 signaling is uniformly suppressed . Then as the spindle and cell elongate, PI3Ks and PTEN move to and function at the poles and furrow, respectively. Cell lines lacking both these enzymatic activities fail to modulate PI(3,4,5)P3 levels, are defective in cytokinesis, and cannot divide in suspension. The cells continue to grow and duplicate their nuclei at a normal rate, generating large multinucleate cells. Furrows that fail to ingress between nuclei are unable to stably accumulate myosin filaments or suppress actin-filled ruffles. We propose that phosphoinositide-linked circuits, similar to those that bring about asymmetry during cell migration, also regulate polarity in cytokinesis. Submitted by: Chris Janetopoulos [cjanetop@jhmi.edu] ----------------------------------------------------------------------------- New prestalk and prespore inducing signals in Dictyostelium Ioannis Serafimidis and Robert R. Kay MRC Laboratory of Molecular Biology, Hills Road, Cambridge, CB2 2QH UK Developmental Biology, in press The differentiation inducing signals (DIFs) currently known in Dictyostelium appear unable to account for the full diversity of cell types produced in development. To search for new signals, we analysed the differentiation in monolayers of cells expressing prestalk (ecmAO, ecmA, ecmO, ecmB and cAR2) and prespore (psA) markers. Expression of each marker drops off as the cell density is reduced, suggesting that cell interaction is required. Expression of each marker is inhibited by cerulenin, an inhibitor of polyketide synthesis, and can be restored by conditioned medium. However, the known stalk-inducing polyketide, DIF-1, could not replace conditioned medium and induce the ecmA or cAR2 prestalk markers, suggesting that they require different polyketide inducers. Polyketide production by fungi is stimulated by cadmium ions, which also dramatically stimulates differentiation in Dictyostelium cell cultures and the accumulation of medium factors. Factors produced with cadmium present were extracted from conditioned medium and fractionated by HPLC. A new factor inducing prespore cell differentiation, called PSI-2, and two inducing stalk cell differentiation (DIFs 6 and 7) were resolved. All are distinct from currently identified factors. DIF-6, but not DIF-7 or PSI-2, appears to have an essential carbonyl group. Thus Dictyostelium may use extensive polyketide signalling in its development. Submitted by: Rob Kay [rrk@mrc-lmb.cam.ac.uk] ----------------------------------------------------------------------------- Dictyostelium LIS1 is a centrosomal protein required for microtubule/cell cortex interactions, nucleus/centrosome linkage and actin dynamics Markus Rehberg, Julia Kleylein-Sohn, Jan Faix, Thi-Hieu Ho, Irene Schulz and Ralph GrŠf* A.-Butenandt-Institut/Zellbiologie, Ludwig-Maximilians-UniversitŠt MŸnchen, Schillerstrasse 42, D-80336 MŸnchen, Germany *corresponding author Mol. Biol. Cell in press The widespread LIS1-proteins were originally identified as the target for sporadic mutations causing lissencephaly in humans. Dictyostelium LIS1 (DdLIS1) is a microtubule-associated protein exhibiting 53 % identity to human LIS1. It colocalizes with dynein at isolated, microtubule-free centrosomes, suggesting that both are integral centrosomal components. Replacement of the DdLIS1 gene by the hypomorphic D327H allele or overexpression of an MBP-DdLIS1 fusion disrupted various dynein-associated functions. Microtubules lost contact with the cell cortex and were dragged behind an unusually motile centrosome. Previously, this phenotype was observed in cells overexpressing fragments of dynein or the XMAP215-homologue DdCP224. DdLIS1 was coprecipitated with DdCP224, suggesting that both act together in dynein-mediated cortical attachment of microtubules. Furthermore, DdLIS1-D327H mutants showed Golgi dispersal and reduced centrosome/nucleus association. Defects in DdLIS1 function also altered actin dynamics characterized by traveling waves of actin polymerization correlated with a reduced F-actin content. DdLIS1 could be involved in actin dynamics through Rho-GTPases, since DdLIS1 interacted directly with Rac1A in vitro. Our results show that DdLIS1 is required for maintenance of the microtubule cytoskeleton, Golgi apparatus and nucleus/centrosome association, and they suggest that LIS1-dependent alterations of actin dynamics could also contribute to defects in neuronal migration in lissencephaly patients. Submitted by: Ralph Graef [rgraef@lrz.uni-muenchen.de] ============================================================================== [End Dicty News, volume 24, number 8]