A hybrid mouse obtained by morulae aggregation of two different reporter mice (GFP and lacZ) allowed Francesca Faggioli and colleagues from the Italian National Research Council to obtain a model in which single cells may be marked differentially with GFP or bgal. So, by finding single cells expressing both reporters (immuno-histochemistry and single-cell PCR), the italian researchers found that cell fusion is a physiological process not only in muscle, throphoblast and osteoclasts, but also in adult mouse liver. This results finally answers long-lived questions about the origins of hepatic polyploidy, that was believed to occur only following DNA duplication and aborted cytokinesis. The two mechanisms aren't mutually exclusive, but Francesca showed us that reporter mice can shed light also on the physiology, because actually they may be considered physiology-respectful models respect to other hard settings (irradiation/ablation regimens, chronic liver damage) used to understand plasticity and cell fusion, with consequent difficulties in discerning whether the results have any physiologic significance or are largely artificial. Of course, the introduction of a foreign gene (the reporter) in any genomic locus, raises questions about the real physiological status of any transgenic organism, however research is in progress to find appropriate reporters with minimal toxicity, and this has a major impact on research community, as recently showed by Rita Stack and Daniel Strongin (University of Chicago) with the development of a safer DsRed protein.
Francesca Faggioli, Maria Grazia Sacco, Lucia Susani, Cristina Montagna, Paolo Vezzoni (2008). Cell fusion is a physiological process in mouse liver Hepatology, 48 (5), 1655-1664 DOI: 10.1002/hep.22488
Rita L Strack, Daniel E Strongin, Dibyendu Bhattacharyya, Wen Tao, Allison Berman, Hal E Broxmeyer, Robert J Keenan, Benjamin S Glick (2008). A noncytotoxic DsRed variant for whole-cell labeling Nature Methods, 5 (11), 955-957 DOI: 10.1038/nmeth.1264