Unique and Shared Functions of Kinesin Light Chain and Milton in Drosophila Oogenesis and Axonal Transport

The roles of Milton and Kinesin light chain (Klc) in ooplasmic streaming and axonal transport in live animals have not been studied. The heavy chain of Kinesin-1 (Khc) contains the ATP-dependent motor domain. Klc is a Khc associated protein long thought to mediate cargo linkage and shown to play a role in Kinesin-1 regulation. However, Milton can compete with Klc for binding to Khc and is thought to be the linker between Khc and mitochondria. To determine the roles of Milton and Klc in vivo, we used both zygotic mutants and RNAi to knockdown Klc and Milton in Drosophila oocytes and larvae and looked for changes in cytoplasmic streaming, Oskar mRNA localization and the axonal transport of both mitochondria and dense core vesicles (DCV). Knockdown of Klc disrupts osk mRNA localization and cytoplasmic streaming, but knockdown of Milton does not. Inhibition of Milton reduces the number of mitochondria in long axons and prevents most movement, but does not affect DCVs. Inhibition of Klc significantly reduces the transport of both mitochondria and DCVs. These data suggest that Klc is working as a critical factor in these Kinesin-1 driven transport events, including a previously undescribed role in mitochondrial transport