CONICET | Buscador de Institutos y Recursos Humanos

In their efforts to maintain intracellular vesiculartransport and the position oforganelles, cells use molecular motors, including myosins that interact or moveon actin filaments. To date, 35 classes of myosin motor proteins have beendescribed in mammaliancells. To determine which myosins participate inthe positioning and morphology of the Golgi apparatus we performed ascreening against 37 mammalian myosins. We took advantage of the?micropatterning technique?, which brings cells to adopt a highly reproducibleshape, and probabilistic density mapping, which quantifies spatial organizationof a particular compartment. Our studies revealed that the knockdown of MYO1Ccauses Golgi apparatus fragmentation and changes the positioning of thisorganelle within the cell. MYO1C is a single-headed class I myosin that isenriched in dynamic regions of the plasma membrane (PM) distinguishedby the presence oflamellipodia, filopodia, and membrane ruffles. This myosin has been previouslyreported to participate in exocytosis, recycling and delivery of severalraft-associated cargoes such as GLUT4, AQP2 and VEGFR to the cell surface. However, its specific functions and partners remain to be elucidated andit is not known how this myosin affects the homeostasis of differentorganelles, particularly the Golgi apparatus. Follow up live cell experiments confirmedthat MYO1C-depletion affects post-Golgi transport, reflected by a slowermovement of Rab6-positivesecretory vesicles. Additionally, we found that MYO1C interacts with theGolgi-specific Brefeldin A-resistance factor 1 (GBF1) by mass spectrometry andco-immune precipitation. GBF1 is a guanine-nucleotide-exchange factor (GEF) ofArf1 and regulates the ER-Golgi interface. The activation of Arf1 by GBF1promotes the recruitment of COP-I involved in the retrograde transport ofproteins from the Golgi to the ER. We observed that MYO1Ccolocalizes with a pool of GBF1 that is found at the PM, and interestingly, thepresence of this PM pool of GBF1 is lost upon depletion of MYO1C. We are currently testing whetherthe absence of MYO1C at the PM induces an increased level of GBF1 at the Golgi,modifying Golgi transport homeostasis, including the secretory pathway, anddisrupting Golgi morphology.