Labeling of Mesencephalic Tegmental Neurons in a Juvenile Pacific Chum Salmon Oncorhynchus keta with Mouse Hippocampal Adeno-Associated Viral Vectors.

Currently, the data on the presence of adenoviral receptors in fish are very limited. We used mouse recombinant adeno-associated viral vectors (rAAV) with a calcium sensor GCaMP6m, which are typically used for the CA1 region of the mouse dorsal hippocampus but have not previously been used for gene delivery in the fish brain. The aim of this work was (1) to assess the ability of the mouse hippocampal rAAV to label brain cells in a juvenile chum salmon Oncorhynchus keta and (2) to determine the phenotype of rAAV-labeled cells. In vivo gene delivery was carried out through intracranial injection of the GFP-tagged rAAV directly into the mesencephalic tegmentum of a yearling chum salmon. The level of infectious efficacy was assessed 1 week after the injection of the vector. Using confocal scanning microscopy, rAAV-GFP expression was assessed in various tegmental areas of a juvenile O. keta, followed by the localization of the neuron-specific protein HuCD tagged with red-fluorescent Alexa Fluor 546. An immunohistochemical analysis combined with DAPI staining revealed rAAV/HuCD colocalization in various neurons of the mouse mesencephalic tegmentum. This finding provides evidence that rAAV-expressing tegmental cells in the juvenile chum salmon refer to a neuron-specific line of brain cells, indicative of the ability of mammalian hippocampal adenoviruses to infect neurons of the fish central nervous system. Thus, mammalian hippocampus-specific rAAVs can incorporate into fish brain neurons with subsequent expression of the viral proteins. It appears that tegmental neurons in a juvenile chum salmon contain a homologue of the mammalian adenoviral receptor. [ABSTRACT FROM AUTHOR]