dictyNews Electronic Edition Volume 43, number 8 April 21, 2017 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 ========= Mroh1, a lysosomal regulator localised by WASH-generated actin Peter A. Thomason, Jason S. King* and Robert H. Insall Address: Cancer Research UK Beatson Institute, Garscube Estate, Switchback Road, Glasgow, G61 1BD, United Kingdom *Present Address: School of Biomedical Sciences, University of Sheffield, Firth Court, Western Bank, Sheffield, S10 2TN, United Kingdom Journal of Cell Science, in press The steps leading to constitutive exocytosis are poorly understood. In Dictyostelium WASH complex mutants, exocytosis is blocked, so cells that take up fluorescent dextran from the medium retain it and remain fluorescent. Here we establish a FACS-based method to select cells that retain fluorescent dextran, allowing identification of mutants with disrupted exocytosis. Screening a pool of random mutants identified the WASH complex, as expected, and multiple mutants in the conserved HEAT-repeat containing protein Mroh1. In mroh1 mutants, endosomes develop normally until the stage where lysosomes neutralize to postlysosomes, but thereafter the WASH complex is recycled inefficiently, and subsequent exocytosis is substantially delayed. Mroh1 protein localizes to lysosomes in mammalian and Dictyostelium cells. In Dictyostelium it accumulates on lysosomes as they mature, and is removed together with WASH shortly before the postlysosomes are exocytosed. WASH-generated F-actin is required for correct subcellular localisation; in WASH complex mutants, and immediately after latrunculin treatment, Mroh1 relocalises from cytoplasm to small vesicles. Thus Mroh1 is involved in a late and hitherto undefined actin-dependent step in exocytosis. submitted by: Robert Insall [r.insall@beatson.gla.ac.uk] ——————————————————————————————————————— Mycobacterium marinum antagonistically induces an autophagic response while repressing the autophagic flux in a TORC1- and ESX-1-dependent manner Elena Cardenal-Muñoz*, Sonia Arafah, Ana Teresa López-Jiménez, Sébastien Kicka, Alexandra Falaise, Frauke Bach, Olivier Schaad, Jason S. King, Monica Hagedorn and Thierry Soldati *Corresponding author PLoS Pathogens, in press http://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1006344 Autophagy is a eukaryotic catabolic process also participating in cell- autonomous defence. Infected host cells generate double-membrane autophagosomes that mature in autolysosomes to engulf, kill and digest cytoplasmic pathogens. However, several bacteria subvert autophagy and benefit from its machinery and functions. Monitoring infection stages by genetics, pharmacology and microscopy, we demonstrate that the ESX-1 secretion system of Mycobacterium marinum, a close relative to M. tuberculosis, upregulates the transcription of autophagy genes, and stimulates autophagosome formation and recruitment to the mycobacteria- containing vacuole (MCV) in the host model organism Dictyostelium. Antagonistically, ESX-1 is also essential to block the autophagic flux and deplete the MCV of proteolytic activity. Activators of the TORC1 complex localize to the MCV in an ESX-1-dependent manner, suggesting an important role in the manipulation of autophagy by mycobacteria. Our findings suggest that the infection by M. marinum activates an autophagic response that is simultaneously repressed and exploited by the bacterium to support its survival inside the MCV. submitted by: Thierry Soldati [thierry.soldati@unige.ch] ============================================================== [End dictyNews, volume 43, number 8]