Animal models for COVID-19.

Abstract: BACKGROUND AND AIMS Despite its superior physiological relevance to human liver metabolism and diseases, the absence of reliable tissue-specific gene manipulation systems has considerably limited genetic research in the Syrian golden hamster (Mesocricetus auratus). The Cre/loxP-based Rosa26-targeted dual-fluorescent reporter system (mT/mG) is widely utilized in murine models for accurate lineage tracing and conditional gene editing. However, such powerful genetic tools are not available for golden hamsters. Herein, we established a functional Rosa26-targeted mT/mG reporter system and a hepatocyte-specific albumin-Cre Recombinase (Alb-Cre) driver line in golden hamsters, providing an important platform for hepatocyte-specific gene manipulation. METHODS The Rosa26 homolog (gRosa26) was identified in the golden hamster genome. Then, a CRISPR/Cas9-based two-cell microinjection system was developed to precisely knock-in gRosa26. The dual-fluorescent Cre reporter (mT/mG) was inserted into gRosa26. Thereafter, a liver-specific Alb-Cre transgenic line was developed using murine Alb enhancer/promoter elements. Finally, Cre-mediated recombination efficiency was evaluated in double transgenic hamsters. RESULTS The gRosa26 locus exhibited >70 % sequence conservation with mice. Golden hamsters with the mT/mG reporter exhibited ubiquitous tdTomato expression, with efficient EGFP activation after Cre-mediated recombination. Furthermore, Alb-Cre transgenic golden hamsters exhibited hepatocyte-specific Cre expression. In double transgenic hamsters, robust hepatocyte-specific tdTomato-to-EGFP recombination was observed by postnatal days 21 and 42. This validated the functionality of the gRosa26-targeted mT/mG system and Alb-driven Cre expression. CONCLUSIONS We reported the development of a functional Rosa26-targeted mT/mG dual-reporter system and a liver-specific Alb-Cre driver in Syrian golden hamsters for the first time. This platform facilitates precise spatiotemporal gene editing in hepatocytes and serves as an essential genetic tool for liver research in this emerging model organism.

TL;DR: In this small series, vascular angiogenesis distinguished the pulmonary pathobiology of Covid-19 from that of equally severe influenza virus infection.