Mice hemizygous for the transgenic insert are viable, fertile, normal in size and do not display any gross physical or behavioral abnormalities. Mice that are homozygous for the transgene are not viable. This transgenic mouse strain expresses Cre recombinase under the control of the human glial fibrillary acidic protein promoter (GFAP). When crossed with a strain containing loxP site flanked sequence of interest, Cre-mediated recombination results in tissue-specific deletion of the target. Recombination occurs primarily in the central nervous system, affecting astrocytes, oligodendroglia, ependyma and some neurons. Expression activity is also present in periportal cells of the liver. Developmental onset of transgene expression occurs in the dorsal and medial regions of the telencephalon by embryonic day 13.5. In adult cerebellum, only astrocytes are immunoreactive for GFAP or Cre recombinase. This mutant mouse strain represents an effective tool for generating central nervous system specific-targeted mutants. <a href="https://www.jax.org/research-and-faculty/resources/cre-repository/characterized-cre-lines-jax-cre-resource">View</a> Cre expression characterization. <a href="https://www.ncbi.nlm.nih.gov/pubmed/32027825">Luo et al. 2020 Neuron 106:37</a> 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 both female and male GFAP-Cre;floxed double mutants bred to floxed mice produced some offspring with germline deletion of the floxed allele [42.9% (6/14) and 50% (9/18) when using Cre female or Cre male, respectively, including some Cre negative offspring]. As such, for Cre-lox experiments, researchers are urged to monitor their Cre;floxed double mutant mice for any undesirable germline deletion of the floxed allele (e.g., genotyping tail/ear samples). Researchers may consider also maintaining a GFAP-Cre colony separate from any floxed colonies. 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 <a href="http://www.informatics.jax.org/allele/MGI:2179048?recomRibbon=open">Mouse Genome Informatics (MGI) Allele Detail entry</a>. For endogenous mouse gene expression, information may also be found searching the <a href="http://www.informatics.jax.org/home/recombinase">MGI Recombinase Activity</a> and <a href="http://www.informatics.jax.org/gxd/recombinasegrid/MGI:95697">MGI Gene Expression + Recombinase Activity Comparison Matrix</a>.

Homozygotes for this transgene are not viable. Hemizygotes express Cre recombinase under the control of the human glial fibrillary acidic protein promoter (GFAP). When crossed with a strain containing loxP site flanked sequence of interest, Cre-mediated recombination results in tissue-specific deletion of the target, and recombination occurs primarily in the central nervous system, affecting astrocytes, oligodendroglia, ependyma and some neurons. This mutant mouse strain represents an effective tool for generating central nervous system specific-targeted mutants.

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