Partial rescue of taste responses of α-gustducin null mice by transgenic expression of α-transducin

The transduction of responses to bitter and sweet compounds utilizes guanine nucleotide binding proteins (G proteins) and their coupled receptors. α-Gustducin, a transducin-like G protein α-subunit, and rod α-transducin are expressed in taste receptor cells. α-Gustducin knockout mice have profoundly diminished behavioral and electrophysiological responses to many bitter and sweet compounds, although these mice retain residual responses to these compounds. α-Gustducin and rod α-transducin are biochemically indistinguishable in their in vitro interactions with retinal phosphodiesterase, rhodopsin and G protein βγ-subunits. To determine if α-transducin can function in taste receptor cells and to compare the function of α-gustducin versus α-transducin in taste transduction in vivo, we generated transgenic mice that express α-transducin under the control of the gustducin promoter in the α-gustducin null background. Immunohistochemistry showed that the α-transducin transgene was expressed in about two-thirds of the α-gustducin lineage of taste receptor cells. Two-bottle preference tests showed that transgenic expression of rod a-transducin partly rescued responses to denatonium benzoate, sucrose and the artificial sweetener SC45647, but not to quinine sulfate. Gustatory nerve recordings showed a partial rescue by the transgene of the response to sucrose, SC45647 and quinine, but not to denatonium. These results demonstrate that α-transducin can function in taste receptor cells and transduce some taste cell responses. Our results also suggest that α-transducin and α-gustducin may differ, at least in part, in their function in these cells, although this conclusion must be qualified because of the limited fidelity of the transgene expression.