dictyNews Electronic Edition Volume 40, number 23 September 12, 2014 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 ========= Abstracts ========= The hybrid type polyketide synthase SteelyA is required for cAMP signalling in early Dictyostelium development Takaaki B. Narita, Zhi-hui Chen, Pauline Schaap and Tamao Saito PLoS One, in press BACK GROUND: In our previous study we found that the expression of stlA showed peaks both in the early and last stages of development and that a product of SteelyA, 4-methyl-5-pentylbenzene-1,3-diol (MPBD), controlled Dictyostelium spore maturation during the latter. In this study we focused on the role of SteelyA in early stage development. PRINCIPAL FINDINGS: Our stlA null mutant showed aggregation delay and abnormally small aggregation territories. Chemotaxis analysis revealed defective cAMP chemotaxis in stlA null mutant. cAMP chemotaxis was restored by MPBD addition during early stage development. Assay for cAMP relay response revealed that the stlA null mutant had lower cAMP accumulation during aggregation, suggesting lower ACA activity than the wild type strain. Exogenous cAMP pulses rescued the aggregation defect of the stlA null strain in the absence of MPBD. Expression analysis of cAMP signalling genes revealed lower expression levels in stlA null mutant during aggregation. CONCLUSION: Our data indicate a regulatory function by SteelyA on cAMP signalling during aggregation and show that SteelyA is indispensable for ACA full induction. Submitted by Tamao Saito [tasaito@sophia.ac.jp] --------------------------------------------------------------------------- Vmp1 regulates PtdIns3P signaling during autophagosome formation in Dictyostelium discoideum Javier Calvo-Garrido, Jason S. King, Sandra Mu–oz-Braceras and Ricardo Escalante Traffic, in press Generation and turnover of PtdIns3P signaling is essential for autophagosome formation and other membrane traffic processes. In both Dictyostelium discoideum and mammalian cells, autophagosomes are formed from specialized regions of the endoplasmic reticulum (ER), called omegasomes, which are enriched in the signaling lipid PtdIns3P. Vmp1 is a multi-spanning membrane protein localized at the ER that is required for autophagosome formation. There are conflicting reports in the literature as to whether Vmp1 is strictly required or not for autophagy-related PtdIns3P signaling and its hierarchical relationship with Atg1 and PI3K. We have now addressed these questions in the Dictyostelium model. We show that Dictyostelium cells lacking Vmp1 have elevated and aberrant PtdIns3P signaling on the ER, resulting in an increased and persistent recruitment of Atg18 and other autophagic proteins. This indicates that Vmp1 is not strictly essential for the generation of PtdIns3P signaling but rather suggests a role in the correct turnover or modulation of this signaling. Of interest, these PtdIns3P-enriched regions of the ER surround ubiquitinated protein aggregates but are unable to form functional autophagosomes. vmp1 null cells also have additional defects in macropinocytosis and growth, that are not shared by other autophagy mutants. Remarkably, we show that these defects and also the aberrant PtdIns3P distribution are largely suppressed by the concomitant loss of Atg1, indicating that aberrant autophagic signaling on the ER inhibits macropinocytosis. These results suggest that Atg1 functions upstream of Vmp1 in this signaling pathway and demonstrates a previously unappreciated link between abnormal autophagy signaling and macropinocytosis. Submitted by Ricardo Escalante [rescalante@iib.uam.es] --------------------------------------------------------------------------- Cellular memory in eukaryotic chemotaxis Monica Skoge1,2 , Haicen Yue2 , Michael Erickstad2, Albert Bae1,2, Herbert Levine3, Alex Groisman2, William F. Loomis1, and Wouter-Jan Rappel2 1 Department of Biology, University of California San Diego, La Jolla, CA 92093 2 Department of Physics, University of California San Diego, La Jolla, CA 92093 3 Center for Theoretical Biological Physics and Department of Bioengineering, Rice University, Houston, TX 77251 PNAS, in press Natural chemical gradients to which cells respond chemotactically are often dynamic, with both spatial and temporal components. A primary example is the social amoeba Dictyostelium, which migrates to the source of traveling waves of chemoattractant as part of a self- organized aggregation process. Despite its physiological importance, little is known about how cells migrate directionally in response to traveling waves. The classic back-of-the-wave problem is how cells chemotax towards the wave source, even though the spatial gradient reverses direction in the back of the wave. Here we address this problem by using microfluidics to expose cells to traveling waves of chemoattractant with varying periods. We find that cells exhibit cellular memory and maintain directed motion towards the wave source in the back of the wave for the natural period of 6 minutes, but increasingly reverse direction for longer wave periods. Further insights into cellular memory are provided by experiments quantifying cell motion and localization of a directional-sensing marker after rapid gradient switches. The results can be explained by a model that couples adaptive directional sensing to bistable cellular memory. Our study shows how spatiotemporal cues can guide cell migration over large distances. Submitted by Wouter-Jan Rappel [rappel@physics.ucsd.edu] ============================================================== [End dictyNews, volume 40, number 23]