FUNCTIONAL CHARACTERIZATION OF AN UNUSUAL ARL13B ORTHOLOGUE IN AN EARLY-DIVERGENT EUKARYOTE

Abstract

The small GTPase Arl13b is associated with Joubert Syndrome – a severe genetic disease caused by defective cilia. Molecular understanding of the Arl13b pathway is only at the very early stage. I have utilized the versatile T. brucei model to study the Arl13b functions in an early diverged, single-flagellated organism. My results show that TbArl13b is a flagellar protein crucial for flagellum biogenesis and cell survival. Different from its metazoan relatives, TbArl13b associates with the axoneme rather than the flagellar membrane. An N-terminus Dimerization/Docking domain is fully responsible for TbArl13b’s localization and axoneme association. Based on results from a novel double inducible RNAi rescue experiment, I propose that the enrichment of the TbArl13b catalytic domain in the flagellar compartment is critical for its cellular functions. Finally, my finding that TbArl13b interacts in vivo with two differentially located Arl3 isoforms hints at a novel bifurcated Arl13b-Arl3 pathway in the trypanosome flagellum.