Non-muscle myosin IIB-like immunoreactivity is present at the drebrin-binding cytoskeleton in neurons.

Dendritic spines are extremely motile, providing a structural mechanism for synaptic plasticity. Actin-myosin interaction is thought to be responsible for the change in the shape of spine. We have already reported that drebrin, an actin-binding protein, inhibits actin-myosin interaction and is enriched in the dendritic spine of mature neurons. In this study, we prepared the actin cytoskeleton of dendritic spines as an immunoprecipitate with anti-drebrin antibody from adult guinea-pig brain, immunized mice with the cytoskeleton, and obtained a monoclonal antibody (MAb) called MAb G650. MAb G650 reacted with non-muscle myosin IIB, but it did not react with muscle myosin II or non-muscle myosin IIA. Immunoblotting with this antibody revealed that drebrin-binding cytoskeleton contains this myosin IIB-like immunreactivity. Immunohistochemistry using MAb G650 demonstrated that this myosin IIB-like immunreactivity can be detected in the neuronal cell bodies and their apical dendrites, where drebrin is hardly detected. These data demonstrate that a myosin subtype associated with drebrin-binding actin filaments in the dendritic spines is myosin IIB, although this myosin is widely distributed in somato-dendritic subdomains of neurons. Furthermore, it is indicated that the cytoskeletons in dendritic spine were uniquely characterized with actin-binding proteins such as drebrin, but not with myosins.