Off-Target Effects in Transgenic Mice: Characterization of Dopamine Transporter (DAT)-Cre Transgenic Mouse Lines Exposes Multiple Non-Dopaminergic Neuronal Clusters Available for Selective Targeting within Limbic Neurocircuitry

Abstract

Transgenic mouse lines are instrumental in our attempt to understand brain function. Promoters driving transgenic expression of the gene encoding Cre recombinase are crucial to ensure selectivity in Cre-mediated targeting of floxed alleles using the Cre-Lox system. For the study of dopamine (DA) neurons, promoter sequences driving expression of the Dopamine transporter (Dat) gene are often implemented and several DAT-Cre transgenic mouse lines have been found to faithfully direct Cre activity to DA neurons. While evaluating an established DAT-Cre mouse line, reporter gene expression was unexpectedly identified in cell somas within the amygdala. To indiscriminately explore Cre activity in DAT-Cre transgenic lines, systematic whole-brain analysis of two DAT-Cre mouse lines was performed upon recombination with different types of floxed reporter alleles. Results were compared with data available from the Allen Institute for Brain Science. The results identified restricted DAT-Cre-driven reporter gene expression in cell clusters within several limbic areas, including amygdaloid and mammillary subnuclei, septum and habenula, areas classically associated with glutamatergic and GABAergic neurotransmission. While no Dat gene expression was detected, ample co-localization between DAT-Cre-driven reporter and markers for glutamatergic and GABAergic neurons was found. Upon viral injection of a fluorescent reporter into the amygdala and habenula, distinct projections from non-dopaminergic DAT-Cre neurons could be distinguished. The study demonstrates that DAT-Cre transgenic mice, beyond their usefulness in recombination of floxed alleles in DA neurons, could be implemented as tools to achieve selective targeting in restricted excitatory and inhibitory neuronal populations within the limbic neurocircuitry.

Polysynaptic inhibition between striatal cholinergic interneurons shapes their network activity patterns in a dopamine-dependent manner

“…Such GABAergic responses and modulation of polysynaptic inhibition were observed also in TH-Cre mice ( Supplementary Fig. 6), although it should be noted that these different mice lines vary in the expression patterns of neurotransmitters in a topographic manner 75,76 .…”

Back and to the Future: From Neurotoxin‐Induced to Human Parkinson's Disease Models

“…Several dopaminergic neuron-specific Cre recombinase expressing mouse lines (DAT-Cre) have also been created (Backman et al, 2006;Ekstrand et al, 2007;Turiault et al, 2007;Zhuang, Masson, Gingrich, Rayport, & Hen, 2005). Despite concerns about specificity of Cre expression (Papathanou, Dumas, Pettersson, Olson, & Wallen-Mackenzie, 2019) and spontaneous tamoxifen-independent recombination ("leakiness") of CreERT2 (Kristianto, Johnson, Zastrow, Radcliff, & Blank, 2017;Sandlesh, Juang, Safina, Higgins, & Gurova, 2018), these mouse lines have been extremely useful to study functions of multiple genes in dopaminergic neurons. For example, analysis of sonic hedgehog (Shh)/DAT-Cre mice revealed that Shh expression in dopaminergic neurons is essential for their maintenance in the adult animals, as the mutant mice exhibited neurodegeneration, locomotor, and gait abnormalities (Gonzalez-Reyes et al, 2012).…”

Human Mesenchymal Stromal Cells Unveil an Unexpected Differentiation Potential toward the Dopaminergic Neuronal Lineage

“…In addition to these key fate-determining transcription factors, fundamental for the midbrain DA neurons development, we also analyzed the expression of the Dopamine active transporter (DAT), which is responsible for dopamine reuptake from the synaptic cleft into the cytosol. DAT gene expression, the gold standard for the identification of mature dopaminergic neurons [16], was undetectable in undifferentiated hFM-MSCs (day 0), then it faintly appeared from day 7 to day 20, becoming abundant at days 29 and 42.…”