The Camk2a (calcium/calmodulin-dependent protein kinase II alpha) gene is expressed predominantly in the adult forebrain. It encodes the &alpha; subunit of a serine-threonine protein kinase that is involved with the regulation of a diverse set of cellular processes, including synaptic plasticity. Significant increases in expression during the second and third postnatal weeks coincides with the most active period of synaptogenesis in the forebrain. In this transgenic strain, a Camk2a gene promoter fragment drives expression of nuclear-localized Cre recombinase. Founder line R1Ag5 (R1ag#5) expresses Cre throughout the adult brain, with high levels in all forebrain structures, and moderate levels in the cerebellum. Moderate levels of Cre expression are also detected in the testis at P30 and P120 by western blot analysis (additional details below). Both the R1Ag5 and R4Ag11 (Stock No. <a href="https://www.jax.org/strain/027400">027400</a>) lines express Cre in the forebrain (mostly cortex and striatum), but the R1Ag5 is much "stronger" than the R4Ag11. Higher levels of Cre are expressed by the R1Ag5 line, earlier in development, and in more widespread neuronal pattern within forebrain neurons. The transgene in these lines is similar to that in the T29 Camk2a-cre line (see Stock No. <a href="https://www.jax.org/strain/005359">005359</a>), but both R1Ag5 and R4Ag11 are reported to have more robust expression. R1Ag5 deletes in both pyramidal neurons and interneurons. R4Ag11 deletes in CA1 but not CA3 pyramidal neurons (in addition to neocortical pyramidal neurons). When R1Ag5 is crossed with an Htt (also known as Hdb) floxed strain, progeny show a greater than 90% reduction in huntington protein in the forebrain. <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 R1ag#5;floxed double mutant males bred to floxed females produced some offspring with germline deletion of the floxed allele. As such, for Cre-lox experiments and to avoid/minimize germline deletion of the floxed allele, researchers may consider breeding R1ag#5 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 <a href="http://www.informatics.jax.org/allele/MGI:2177769?recomRibbon=open">Mouse Genome Informatics (MGI) Allele Detail entry</a>. This same 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:88256">MGI Gene Expression + Recombinase Activity Comparison Matrix</a>.

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These R1Ag5 (R1ag#5) mice express nuclear-localized Cre recombinase from the mouse Camk2a promoter in the adult brain, with high levels in all forebrain structures, and moderate levels in the cerebellum as well as testis.

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