The β-GsD (or β-R-s) transgene has the rat insulin 2 promoter directing expression of a hemagglutinin epitope-tagged, mutant G protein-coupled receptor (GsD [also called rM3Ds or R-s]) to pancreatic β-cells.
The GsD is a G_s-coupled rat muscarinic 3 DREADD modified to have its second and third intracellular loops replaced with the corresponding turkey β1-adrenergic receptor sequences. Two amino acid substitutions (Y148C and A238G) have been added that abolish receptor affinity for the native ligand, acetylcholine (ACh), but allow receptor binding and subsequent activation by the small pharmacologically inert molecule clozapine-N-oxide (CNO). CNO binding to GsD induces the selective activation of the canonical Gα_s signaling pathway, effectively increasing intracellular cAMP levels.

Mice that are hemizygous for the transgene (β-GsD Tg or β-R-s Tg) are viable and fertile. The donating investigator reports they have not tried to generate homozygous mice (May 2016). The phenotype described below compares β-GsD Tg with a similarly created transgenic mouse that expresses a rat insulin 2 promoter-driven rhM3Dq (β-rhM3Dq Tg ; Stock No. 028964).

The transgenic mouse lines β-rhM3Dq Tg (Stock No. 028964) and β-GsD Tg (Stock No. 028966) express similar numbers of rhM3Dq and GsD in their pancreatic islets, respectively. RT-PCR studies confirmed that rhM3Dq and GsD transcripts were not detectable in tissues other than pancreatic islets.

In the absence of CNO, both transgenic lines have normal growth, insulin sensitivity, plasma insulin levels and glucagon levels. While freely-fed β-rhM3Dq Tg have normal blood glucose levels, freely-fed β-GsD Tg have decreased blood glucose levels. Taken together, this indicates the rhM3Dq receptor is devoid of ligand-independent signaling in vivo, whereas the GsD receptor retains some degree of agonist-independent signaling in vivo.

CNO treatment of transgenic mice leads to the activation of β-cell G_q/11 or Gα_s signaling pathways, respectively, in a conditional and β-cell-selective fashion.
Specifically, following CNO administration in β-rhM3Dq Tg, the canonical G_q/11 pathway is activated in rhM3Dq-expressing pancreatic β-cells. This leads to significant increases in both first- and second-phase insulin release, greatly improved glucose tolerance in obese, insulin-resistant mice, and elevated β-cell mass, associated with pathway-specific alterations in islet gene expression levels. For β-GsD Tg, CNO-induced activation of the canonical Gα_s pathway in GsD-expressing pancreatic β-cells results in qualitatively similar in vivo metabolic effects.