|Ph.D Thesis||Department of Biology|
|Supervisor:||Prof. Zilberstein Dan|
Leishmania are the causative agents of a wide range of visceral and cutaneous diseases in humans. Following changes in the environment Leishmania undergo a developmental transformation between the extracellular promastigote form in the sand fly vector and the obligatory intracellular amastigote form in phagolysosomes of human macrophages. The aim of my work was to understand the mechanisms that mediate the differentiation signal and initiate promastigote to amastigote differentiation in L. donovani. Specific objectives were: a)
to investigate cell cycle regulation of differentiation; b) to reveal the signal transduction pathways that mediate the differentiation signal and c) to identify genes involved in these processes.
A host-free differentiation system that was developed in our laboratory was used in this study. In this system exposing promastigotes to pH 5.5 and 370C (differentiation signal), trigger promastigote to amastigote differentiation. We found that this signal induced transient cell cycle arrest at G1 for 3 hours and chromatin condensation. We showed that parasite exposure to 370C induced the protein-misfolding signaling pathway, causing the exit of parasite cells from the cell cycle. Acidic pH releases the cells from arrest and routes them into differentiation. Using genomic and proteomic approaches we identified a few genes that are differentially expressed during promastigote to amastigote differentiation. These genes will be utilized to further investigate the differentiation process and its regulation.