Figure 3. Schematic of genetic rescue of the α3 knockout in noradrenergic neurons.

A. α3KO and Rescue alleles. theα3KO allele (top) has integrated the insertion-type gene targeting vector for single reciprocal recombination in its entirety¹⁸. It carries an artificial exon (light green, 5*) flanked by loxP sites (red), targeting vector-derived homologous genomic sequences (light brown) and the plasmid backbone of the targeting vector (blue). Genomic sequences that were not included in the targeting vector are shown as dark brown. The most relevant feature is that the α3KO allele contains the endogenous exon 5 (dark green, 5) and an artificial exon 5 (light green, 5*), which results messenger RNA (mRNA) degradation, which is the likely mechanism of the α3 knockout²⁰. In the Rescue allele, elimination of the artificial exon by Cre-loxP-mediated recombination results in α3 mRNA (orange) being made and thus the expression of the α3 subunit being restored.

B. Exonic structure of predicted gene products from wild type (WT), α3KO and Rescue allele. Presence of the artificial exon 5, 5*, in the α3KO results in mRNA breakdown and thus a functional knockout. The exonic structure of wild type (WT) and Rescue alleles is identical.