Mice hemizygous for the Gfap-cre transgene are viable and fertile, with a mouse glial fibrillary acidic protein (mGfap) promoter sequence directing expression of Cre recombinase. When GFAP-Cre line 77.6 mice are bred with mice containing a loxP-flanked sequence, Cre-mediated recombination is expected to result in deletion of the floxed sequences in the Cre recombinase-expressing tissues of the offspring.

Specifically, Cre recombinase activity (as defined by expression of a floxed-STOP reporter gene) is targeted to most astrocytes throughout healthy brain and spinal cord tissues, and to essentially all astrocytes following central nervous system (CNS) injury. Some germline expression is observed (see below).

These GFAP-Cre line 77.6 mice (Stock No. 024098) also have Cre recombinase activity in a subpopulation of adult neural stem cells in the subventricular zone. In contrast to GFAP-Cre line 73.12 (Stock No. 012886), GFAP-Cre line 77.6 mice are reported to have no Cre recombinase activity in postnatal or adult neural stem cells (or their progeny) from the hippocampus or other brain regions. As such, GFAP-Cre line 77.6 mice are particularly useful for selective targeting of astrocytes. Additionally, the donating investigator reports GFAP-Cre lines 73.12 and 77.6 have cre expression in the male germline, and suggests breeding GFAP-Cre females with floxed males for Cre-lox experiments.

Furthermore, Luo et al. 2020 Neuron 106:37 Table 1 shows germline recombination in offspring (F2) of Cre;floxed double mutant (F1) mice bred to floxed and/or wildtype mice. The authors also note that in general, the frequency of recombination in Cre;floxed double mutant germline cells appears to be considerably higher than in zygotes produced by breeding Cre mice to floxed mice.
This reports that GFAP-Cre line 77.6;floxed double mutant males bred to floxed females produced some offspring with germline deletion of the floxed allele [observed from several cohorts (including up to 100% in a few litters)]. As such, for Cre-lox experiments and to avoid/minimize germline deletion of the floxed allele, researchers may consider breeding GFAP-Cre line 77.6 females to floxed males.

If the recombinase activity pattern of this allele is further characterized by the Genetic Resource Science group at The Jackson Laboratory, such findings will be reported on the Mouse Genome Informatics (MGI) Allele Detail entry. This same information may also be found searching the MGI Recombinase Activity and MGI Gene Expression + Recombinase Activity Comparison Matrix.