The SERT-cre (SERTcre) "knock-in" allele has a nuclear-localized Cre recombinase inserted just upstream of the first coding ATG of the serotonin transporter gene (Slc6a4 ; SERT or 5-HTT). This was designed to both abolish SERT gene function and place Cre recombinase expression under the control of the SERT promoter/enhancer elements.
Cre recombinase activity is directed to serotonergic neurons. In adult mice, Cre recombinase activity is predominantly observed in serotonin producing neurons of the brain (raphe nuclei) and the gut (enterochromaffin cells). During development, Cre recombinase activity is observed in thalamus, cingulate cortex and hippocampus CA3 region pyramidal cells, as well as more broadly in several non-serotonin neurons of the brain and in neural crest derivatives. While SERT expression is not expected in adult thalamus, cingulate cortex or hippocampus CA3 region pyramidal cells, Cre reporter staining observed in these adult tissues may be attributed to SERT expression patterns during late embryonic and early postnatal development.
Homozygous SERT-cre mice are viable and fertile. Failure of serotonin uptake/clearance results in behavioral, neurological, and biochemical abnormalities (donating investigator points to PMID 17356573, Sanders, 2007). Heterozygotes have no known phenotype.
Of note, breeding homozygous SERT-Cre females with Cre reporter males results in sporadic germline cre expression (presumably due mainly to SERT expression in murine ovarian cells). For experiments, the donating investigator recommends breeding heterozygous SERT-Cre males with Cre reporter females as the frequency of germline cre expression is greatly diminished.
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 both female and male SERT-Cre;floxed double mutants bred to floxed mice produced some offspring with germline deletion of the floxed allele [observed from >20 litters (up to 100% in some litters) when using Cre female or Cre male]. As such, for Cre-lox experiments and to reduce the frequency of germline deletion of the floxed allele, researchers may consider breeding SERT-Cre heterozygous mice to floxed mice.
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.
SERT-deficient mice on a C57BL/6 congenic background are also available (see Stock No. 008355).
