"Firefly rats" as an organ/cellular source for long-term in vivo bioluminescent imaging

Transplantation research involving the use of stem cells demands an appropriate in vivo visualization system to monitor cellular fate over an observation period. The new field of in vivo imaging is being developed with fluorescent and luminescent biotechnology, and involves the real-time visualization of complex cellular processes in living animals.

: Following our recent development of inbred green fluorescent protein (GFP)-transgenic (Tg) rats, we created the establishment of inbred (Lewis) Tg rats with firefly luciferase. The immunogenicity against luciferase was evaluated by the skin grafting test, and the fate of grafts was monitored by in vivo luminescent technique.

: The luciferase-Tg rats ubiquitously expressed the marker gene. Conventional skin grafting apparently showed the long-term acceptance of luciferase-Tg rat skin on wild-type rats (>100 days), compared with grafting of GFP-Tg-derived skin (<10 days). This suggests less cellular immune responsiveness against the luciferase protein than GFP. Strikingly, organ transplants with heart and small bowel, and bone marrow cell transplantation showed viability and graft acceptance, demonstrating that cells and organs from luciferase-Tg rats are transplantable and their fate can be tracked for a sufficient time. Taking advantage of less immunogenic luciferase, cellular fate of transplanted mature hepatocytes was also examined. Transplanted hepatocytes proliferated and were monitored selectively in damaged liver, but not in healthy liver, for over 60 days.

We propose on the basis of these findings that the luciferase-Tg rat system with modern optical imaging offers a new platform for a better understanding of stem cell biology and transplantation.