Mice hemizygous for the BAC Viaat-cre transgene are viable and fertile, with solute carrier family 32 (GABA vesicular transporter), member 1 (Slc32a1 or Viaat) promoter/enhancer regions driving expression of cre-recombinase. The modified BAC also contained the truncated coding sequence of the actin-related protein 5 homolog (Actr5) gene, but no ACTR5 over-expression was seen. VIAAT, expressed in γ-amino-butyric-acid-(GABA)-ergic neurons, is a transporter required for loading GABA and glycine into synaptic vesicles.

When these BAC Viaat-cre mice are bred with mice containing loxP-flanked sequence, Cre-mediated recombination will result in deletion of the floxed sequences in GABAergic neurons of the offspring. These mice may be useful for studying GABAergic neuronal function.
For example, when bred to B6;129P2-Mecp2^tm1Bird/J mice (Stock No. 006847), these mice exhibit behaviors common to those seen in Rett Syndrome and Autism Spectrum Disorders including repetitive behaviors, progressive motor dysfunction and weakness, respiratory dysfunction, learning and memory deficits, and premature lethality.

In 2017 the donating investigator reported that germline transmission of recombined floxed alleles is noted in F2 offspring when the BAC Viaat-cre transgene and floxed allele are present in F1 male breeders. Therefore, when it is necessary to have the BAC Viaat-Cre transgene and floxed alleles together prior to the final experimental cross, it is highly suggested to use female breeders that contain a floxed allele(s) and this transgene. For best practice, it is suggested to continually screen for signs of germline transmission of recombined floxed alleles and to cross in this transgene with a conditional allele as late in the breeding scheme as possible.

Similarly, Luo et al. 2020 Neuron 106:37 Table 1 reports that BAC Viaat-cre;floxed double mutant males bred to floxed females produced some offspring with germline deletion of the floxed allele [60.9% (14/23)]. 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. As such, for Cre-lox experiments and to avoid/minimize germline deletion of the floxed allele, researchers may consider breeding BAC Viaat-cre 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.