Separate but linked functions of conventional myosins modulate adhesion and neurite outgrowth

The potential functional diversity of closely related myosin isoforms found in eukaryotic cells is not yet understood in detail. We have previously provided evidence from functional knockouts of Neuro-2A neuroblastoma cells that myosin IIB is essential for neurite outgrowth. Here we investigate the role of non-muscle myosin IIA in the same cell line. We show that suppression of myosin IIA transcript and protein expression, brought about through exposure to isoform-specific antisense oligonucleotides, caused a rearrangement of the actin cytoskeleton and loss of cell adhesion. This also led to disruption of focal contacts, as evidenced by coincident reduction in paxillin and vinculin immunofluorescence, but did not diminish transcript expression. All effects were fully reversible. Before myosin IIA antisense-induced detachment, neurite outgrowth remained unaffected. By contrast, antisense oligonucleotides directed against myosin IIB transcripts had no effect on adhesion but severely attenuated neurite outgrowth. We infer that the two main isoforms of neuronal conventional myosin, myosins IIA and IIB, have separate but linked functions during neuronal adhesion and neurite outgrowth.