In vivo transduction of central neurons using recombinant Sindbis virus: Golgi-like labeling of dendrites and axons with membrane-targeted fluorescent proteins.

A new recombinant virus which labeled the infected neurons in a Golgi stain-like fashion was developed. The virus was based on a replication-defective Sindbis virus and was designed to express green fluorescent protein with a palmitoylation signal (palGFP). When the virus was injected into the ventrobasal thalamic nuclei, many neurons were visualized with the fluorescence of palGFP in the injection site. The labeling was enhanced by immunocytochemical staining with an antibody to green fluorescent protein to show the entire configuration of the dendrites. Thalamocortical axons of the infected neurons were also intensely immunostained in the somatosensory cortex. In contrast to palGFP, when DsRed with the same palmitoylation signal (palDsRed) was introduced into neurons with the Sindbis virus, palDsRed neither visualized the infected neurons in a Golgi stain-like manner nor stained projecting axons in the cerebral cortex. The palDsRed appeared to be aggregated or accumulated in some organelles in the infected neurons. Anterograde labeling with palGFP Sindbis virus was very intense, not only in thalamocortical neurons but also in callosal, striatonigral, and nigrostriatal neurons. Occasionally there were retrogradely labeled neurons that showed Golgi stain-like images. These results indicate that palGFP Sindbis virus can be used as an excellent anterograde tracer in the central nervous system.