I wonder whether it is known by now where the CD4-Cre transgene established by Christopher B. Wilson integrated into the DNA and whether therefore a conventional PCR would be possible to distinguish hemizygous from homozygous animals?
Could be tricky. Even if you think to use copy-number specific qRT-PCR, you have to have a reliable reference. I guess that even in a "heterozygote" mouse, there are more than a single copy of the transgene at the integration site. Classically, you have to do a "Test-Cross" with a wt mouse, and then count the % of Cre+ offspring to deduce if the Cre+ parent was homo- or heterozygote. But this is time consuming and perhaps not what you want. Earlier in life, you could do FISH for the transgene to check if you see one or two signals. Maybe this works even on some extraembryonic tissues.
Michael
I came across this paper while trying to find a reliable way to determine zygosity of my own Cre animals, although I never ended up trying it out. It requires qRT-PCR however. It'll be difficult to determine zygosity of Cre mice by conventional PCR.
Since people still seem to read this question, I would like to point everyone to this work of my former colleague that describes the insertion point of the CD4-Cre transgene and also includes a novel PCR method for their genotyping that includes distinction of hemizygous and homozygous animals. Article Chromosomal localisation of the CD4cre transgene in B6·Cg-Tg...
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