Investigations into the biochemical and cellular biology of a cytoplasmic dynein mutation, abnormal rear leg (Arl)

The aim of this project was to investigate the effects of a novel mouse cytoplasmic dynein mutation; Abnormal rear leg (Arl). Cytoplasmic dynein is a microtubule (MT) based motor protein important for diverse cellular processes including Golgi maintenance and retrograde transport of organelles. Arl is a mouse point mutation in the heavy chain subunit of dynein (Dync1h1). Homozygous Dync1h1Arl/Arl die at embryonic day 10. Dync1h1Arl/+ heterozygotes have a normal life span, but exhibit abnormal gait and hindlimb clasping during tail suspension, typical of neuronal dysfunction. Protein purification from wildtype and heterozygous brain tissue showed increased MT binding in Dync1h1Arl/+ compared to wildtype. Delayed endosomal trafficking was observed in EGF stimulated Dync1h1Arl/+ mouse embryonic fibroblasts (MEFs) compared to wildtype, in both fixed cells and using live cell imaging. Similarly, a delay in the reassembly of the Golgi complex after disruption with a MT depolymerisation agent, nocodazole, was observed in Dync1h1Arl/+ MEFs compared to wildtype. In addition, the Golgi complex was observed as being structurally perturbed in Dync1h1Arl/+ lumbar spinal cord neurons using transmission electron microscopy (TEM) compared to the wildtype. TEM also revealed that the mitochondria were structurally perturbed in Dync1h1Arl/+ lumbar spinal cord neurons compared to wildtype, and O2 consumption assays investigating their function showed the Dync1h1Arl/+ mitochondria to have increased respiration rates compared to wildtype. Thus, these data highlight the Arl mouse as an invaluable model for studying the mechanism of dynein function and the subsequent outcomes when they are compromised.