I made a knock-in mouse line expressing EGFP and was able to detect
fluorescence directly in platelets and spleenocytes as
predicted by FACS. However, I was not able to see any good signal in
tissue sections from cryosection fixed with 4% paraformaldehyde (too much
background) or immunohistachemistry from parafin section using polyclonal
antibodies (clontech). I'd love to hear from people who worked a lot on
GFP expression in transgenic mice.