A Herpes Simplex Virus Type 1 Vector as Marker for Retrograde Neuronal Tracing: Characterization of lacZ Transcription and Localization of Labelled Neuronal Cells in Sensory and Autonomic Ganglia after Inoculation of the Anterior Segment of the Eye

Herpes simplex virus type 1 (HSV-1) is a human, neurotropic pathogen which also can infect experimental animals. Much interest has been focused on genetic modification of HSV-1 so that it can be used as a vector for gene delivery and for tracing neuronal connections. For expression of a foreign gene inserted into the HSV-1 genome, both the site of insertion and the promoter activity are important. We have used a previously described HSV-1 vector, KOS/58, to demonstrate that the β-galactosidase gene inserted together with a neurofilament L promoter into the coding region of the glycoprotein C (gC) gene is under the control of the foreign promoter rather than under that of the gC gene. This was performed by isolation of RNA from infected, neuron-like PC12 cells and Northern blotting using probes from various regions of the modified part of the genome. The vector was then inoculated in the cornea, subconjunctivally, or into the anterior chamber of the mouse eye. Whole mounts of the trigeminal, superior cervical and pterygopalatine ganglions were stained for β-galactosidase. The localization of labelled neurons was consistent with retrograde axonal transport as the principal way of neuronal infection indicating that KOS/58 could be used as a retrograde tracer. The position of the labelled cells suggests a somatotopic organization of the mouse trigeminal and superior cervical ganglion similar to that of rats and rabbits.