Myosin-1d expression and dynamics in polarized cells

Abstract

Class I myosins are monomeric actin-binding, ATP hydrolyzing molecular motors that are expressed in a variety of cell types, and function at the membrane-actin interface. Myosin-1d, one of eight vertebrate class I myosins, is expressed in polarized cells of the small intestine and nervous system, but subcellular localization and function for the motor remains largely unexplored. Intriguingly, myosin-1d is coexpressed in epithelial cells of the small intestine with myosin-a, where both motors target to the well-defined apical actin array of the brush border. However, how similar class I motors compartmentalize subcellularly is unknown, and raises the question of functional overlap. Interestingly, we found that myosin-1d and myosin1a exhibit differential localization and this partitioning can be explained by differential dynamics. Moreover, myosin-1d redistributes along the microvillar actin bundle in the absence of myosin-1a in MYO1A knockout animals. This suggests that class I myosins do have unique functions in wildtype, but may compensate for loss of activity. Interestingly, our data demonstrates that myosin-1d has a different subcellular localization in the nervous system. In these polarized cells, myosin-1d exhibits a punctate distribution in neuronal dendrites, cell bodies, and axons. We observed prominent expression in Purkinje cells and a subset of granule cells, with both patterns developmentally regulated. However, myosin-1d was not detectable in oligodendrocytes during early development. In the PNS, we observed that myosin-1d is present in neurons, and myelinating Schwann cells. This suggests a differential role for the motor in myelinating cells between the two nervous systems. Our studies also revealed that myosin-1d interacts with aspartoacylase, a catalytic enzyme involved in fatty acid synthesis that is widely expressed in similar polarized cells as myosin-1d. Together, these studies suggest that myosin-1d has distinct localization patterns in different polarized cell types, but may modulate aspartoacylase activity.