Transgenic zebrafish support the replication of mammalian prions

Introduction. Zebrafish are a powerful model for studying vertebrate brain development and neurological disorders. Their genetic tractability and suitability for in vivo imaging make them attractive for studying dynamic processes such as prion propagation and neurodegeneration. Prion toxicity may require specific proteins or pathways absent or functionally divergent in zebrafish.

Objectives. We aimed to generate zebrafish lines expressing ovine PrPC to assess their susceptibility to ovine prions.

Methods. The ovine PrP gene (VRQ allele) was placed under the zebrafish ß-actin promoter and introduced using the Tol2 transposon system. Transgenic lines were bred to the F4 generation and characterized for PrPC expression, growth, survival and behavior. Transgenic and wild-type zebrafish were inoculated with a 127S scrapie prion strain by intraperitoneal or intraventricular routes. Fish were monitored for clinical signs and euthanized at end life for prion detection by PMCA and RT-QuIC.

Results and Discussion. Three transgenic lines showed stable homogeneous PrPC expression at physiological levels (approximately 1x), with normal glycosylation and truncation patterns. Growth, reproduction, and behavior were normal in uninfected animals.

No typical clinical signs were observed in 127S-inoculated fish over 1000 days, yet ~25% of transgenic fish tested positive for prions in brain tissue. Wild-type fish remained negative, suggesting true prion replication. Prion detection in the spleen was inconsistent, suggesting direct neuroinvasion process. Back-transmissions to ovinized tg338 mice are ongoing and suggest maintaining of strain properties.

Conclusions.Transgenic zebrafish expressing ovine PrP can replicate prions subclinically and may provide new insights into prion neurotoxicity and resistance mechanisms.