CHARACTERIZATION OF THE ORGANELLE-ANCHORING MACHINERY ACTING IN HUMAN GENETIC DISORDERS BASED ON DEFECTS IN ORGANELLE MOTILITY USING AN YEAST MODEL SYSTEM

Mammalian melanosomes undergo long-range bi-directional movement via microtubule-based transport. They are then retained in peripheral dendrides of melanocytes to be subsequently transferred to keratinocytes. Melanosome capturing at the melanocyte dendrides is essential for their transfer, and hence, for normal pigmentation. The Griscelli Syndrome belongs to a group of lysosomal-related dysfunctions that comprises the Hermansky-Pudlak Syndrome (HPS), the Chediak-Higashi Syndrome (CHS), and Chorideraemia. These dysfunctions have common clinical traits such as pigmentary dilution of the skin and hair that can be associated with oculocutaneous albinism and platelet storage pool deficiency and/or neurological manifestations. At the molecular level they are due to the genetic inactivation of genes encoding either the class V myosin MyoVA or the Rab/Ypt protein Rab27 or proteins regulating organelle movement. Rab27/class V myosin complex formation is essential for melanosome capturing at the extremities of melanocyte dendrides and for their peripheral movement. The remarkable evolutionary conservation of the molecular machinery regulating vesicle/organelle movement between yeast and humans opens the possibility of using the genetic system of the yeast Saccharomyces cerevisiae to characterize the cellular processes in which Rab/Ypt protein interaction with class V myosin is required. This project specifically aims to isolate additional components of the Rab/Ypt-myosin V complex and to understand which signals regulate the formation of this complex by using the genetic system of the yeast S.cerevisiae and to report the data obtained to isolate the homologues in human cells. Such an integrated approach has been previously shown to be fundamental for an understanding of the molecular bases of disorders based on the dysfunction of genes involved in cell cycle progression and signal transduction and for the identification of novel molecular targets for direct therapeutic study