Eukaryotic cells use microtubule tracks to move cargo over long distances. There are two types of molecular motors that move on microtubules: dyneins and kinesins. Dyneins move cargo towards the minus ends of microtubules, typically towards the cell interior. Kinesins move cargo in the opposite direction, generally towards the cell surface. Our lab is tackling three broad questions.

  1. How does the dynein motor work and how is it regulated?
  2. What are the rules governing transport in cells?
  3. Why do defects in transport cause disease?

 How does the dynein motor work and how is it regulated?

Cytoplasmic dynein-1 is the only motor used for long-distance minus-end-directed microtubule-based trafficking in eukaryotic cells ranging from human neurons to the hyphae of filamentous fungi. Yet, it transports dozens, if not hundreds of different cargos. One of our lab’s goals is to understand how this large, multi-subunit, motor is regulated. Dynein has two regulators that are conserved and required for most (perhaps all) of its functions: the dynactin complex and Lis1/ Nudel. Current experiments in the lab are focused on determining how these regulators work. We use quantitative approaches to do this, including single-molecule imaging, cryo-electron microscopy (in collaboration with the lab of Andres Leschziner), proteomics, and live-cell imaging.

What are the rules governing transport?

In addition to cytoplasmic dynein-1, at least 15 kinesin motors (in humans) are responsible for moving cargo in the opposite direction as dynein. This small subset of motors is responsible for nearly all long distance transport in eukaryotic cells. What is the full list of dynein and kinesin cargos? What links the motors to different cargos? How is specificity achieved? Do all cargos have a distinct mechanism for recruiting motors? We are addressing these questions using two different discovery-based approaches.

We use the filamentous fungus, Aspergillus nidulans, as a powerful genetic system to dissect microtubule-based transport. We have conducted screens to identify genes required for the transport of endosomes, peroxisomes, and nuclei. Current projects in the lab are characterizing these novel transport factors.

We also use proteomic approaches to identify the dynein and kinesin “transportome”. Current efforts in the lab are focused on using proximity-dependent labeling in living human cells to identify the dynein/ dynactin interactome as well as the interactome of distinct dynein "activators", such as the BICD and HOOK family activators.

Why do defects in transport cause disease?

Mutations in every component of the transport system—tubulins (the building blocks of microtubules), dynein, kinesins, and proteins that regulate the motors or their tracks—cause neurological diseases. For example, mutations in cytoplasmic dynein-1 cause a peripheral neuropathy called Charcot Marie Tooth type 2, Spinal Muscular Atrophy- Lower Extremity Dominant (SMA-LED), malformation of cortical development, and intellectual disability. Like some mutations in dynein, mutations in the dynein activator BICD2 also cause SMA-LED. Mutations in a subunit of dynactin result in motor neuron disease and Perry syndrome, an early onset form of Parkinson’s disease. Defects in microtubule-based axonal transport are also observed in other neurodegenerative diseases including Amyotrophic Lateral Sclerosis, Alzheimer’s and Huntington’s, suggesting that there may be additional links between dynein and neurological disease yet to be uncovered. One hypothesis is that neurodegenerative diseases can result from the compromised trafficking of particular cargos. Current projects in the lab are aimed at identifying which cargos or points of regulation are defective in disease states.

This video shows early endosomes (labeled with RabA-tagGFP) trafficking in an Aspergillus nidulans hypha, imaged using a lattice light-sheet microscope. (Frame size: 76 x 26 x 11 um)