Identification of a Novel Link between the Motor Proteins Dynein and Kinesin-1

Abstract

The motor proteins dynein and kinesin are fascinating biological machines which, like vehicles in a city, move various cellular cargoes along cytoskeletal microtubules (MT). In filamentous fungi, these motors are important for the hyphal growth, which is characterized by localized extension at the tip of the apical hyphal cell. This type of growth requires the movement of a large number of vesicles from and to the hyphal tip in order to support the continuous addition of new plasma membrane and cell wall. Recent studies in filamentous fungi, have shown that early endosomes (EEs) are specifically recognized and moved by dynein from the MT plus-ends at the hyphal tips to more distal cellular compartments. Interestingly, the targeting of dynein to MT plus-ends, is dependent on kinesin-1, and its disruption lead to an aberrant accumulation of EEs at hyphal tips and a reduction in mycelial expansion. While great advances have been made in our understanding of dynein interaction with its specific cargoes, the mechanism of its interaction with kinesin-1 have remained unknown. In an effort to expand our understanding of dynein physical and regulatory interactions, we employed genetic, molecular, and fluorescence microscopy techniques to isolate and analyze mutants affected in hyphal growth and in the localization of cytoplasmic dynein in the model organism Neurosporacrassa. Here we report the identification of a novel protein, which is required for the physical interaction between dynein and kinesin-1 during their journey to the hyphal tip. Interestingly, this protein is only detected in the genomes of the filamentous Ascomycota species but have the ability to physically interact with Drosophila kinesin-1, DmKHC.