Targeting Cre recombinase to specific neuron populations with bacterial artificial chromosome constructs

Abstract

Transgenic mouse lines are characterized with Cre recombinase driven by promoters of CNS-specific genes using bacterial artificial chromosome (BAC) constructs. BAC-Cre constructs for 10 genes (Chat, Th, Slc6a4, Slc6a2, Etv1, Ntsr1, Drd2, Drd1, Pcp2, and Cmtm5) produced 14 lines with Cre expression in specific neuronal and glial populations in the brain. These Cre driver lines add functional utility to the >500 BAC-EGFP (enhanced green fluorescent protein) transgenic mouse lines that are part of the Gene Expression Nervous System Atlas Project.

Figure 1.

Cre expression directed to dopaminergic (A), serotonergic (B), and cholinergic (C) neurons in BAC-Cre transgenic mouse lines. A, Dopaminergic neurons are labeled in a Th BAC-Cre transgenic line with Cre expression localized in neurons in the midbrain substantia nigra pars compacta (Th BAC-CRE; green), which colocalize with Th-IR. There is a nearly complete overlap of TH Cre-driven EGFP labeling and Th-IR (insets). B, In a serotonin transporter (Slca4) BAC-Cre transgenic line, Cre is directed to serotonergic neurons in the dorsal raphe nucleus in the dorsal midbrain, which coexpress serotonin-synthesizing enzyme, tryptophan hydroxylase-IR. Insets, There is a nearly complete overlap of Slca4 Cre-driven EGFP labeling and tryptophan hydroxylase-IR in neurons in the dorsal raphe. C, In a Chat BAC-Cre transgenic line, labeled neurons in the basal forebrain coexpress Chat immunoreactivity (ChAT-IR).

Figure 2.

Cre expression in forebrain circuits, with labeling of specific neuronal projection systems in the cerebral cortex (A, Etv1; B, Ntsr1) and striatum (C, Drd2; D, Drd1a). Expression is produced in layer 5 corticostriatal neurons in an Etv1 BAC-Cre line (A, Etv1). Cre is expressed in layer 6 corticothalamic neurons in an ntsr1 BAC-Cre line (B, Ntsr1). Clearly labeled are the projection axons of these neurons, which terminate in the dorsal thalamic nuclei. In the striatum, the majority of neurons are medium spiny projection neurons, which are evenly divided into striatopallidal (indirect pathway) and striatonigral (direct pathway) neurons, which selectively express the drd2 and drd1a dopamine receptors, respectively. Cre expression produced in Drd2 BAC-Cre lines (C, Drd2) is directed to striatopallidal neurons. In this line, labeled neurons in the striatum extend axons that terminate in the globus pallidus external segment (GPe). In contrast, expression produced in Drd1a BAC-Cre lines (D, Drd1a) is directed to striatonigral neurons, which have axons that extend through the globus pallidus to terminate in the internal segment of the globus pallidus (GPi) and substantia nigra (not shown).

Figure 3.

A, A Pcp2 BAC-Cre transgenic line produces Cre expression that is restricted to the cerebellum localized to Purkinje cell neurons as seen in a sagittal brain section. B, A Cmtm5 BAC-Cre transgenic line produces Cre expression in oligodendrocyte cells throughout the brain. Bi, Labeled cells in a forebrain area including the cerebral cortex, underlying white matter, and striatum are seen to have the morphology of oligodendrocytes. C, Inducible Cre expression occurs in a serotonin transporter (Slca4) BAC-ER-Cre transgenic line. Mice treated with saline show no Cre expression, whereas a single treatment with tamoxifen (6 mg/kg, i.p.) produces Cre expression in serotonin neurons in the dorsal raphe.