Expression of the metabotropic glutamate receptor 5 (mGluR5) induces melanoma in transgenic mice.

Glutamate is the major excitatory neurotransmitter in the mammalian CNS and mediates fast synaptic transmission upon activation of glutamate-gated ion channels. In addition, glutamate modulates a variety of other synaptic responses and intracellular signaling by activating metabotropic glutamate receptors (mGluRs), which are G protein-coupled receptors. The mGluRs are also expressed in nonneuronal tissues and are implicated in a variety of normal biological functions as well as diseases. To study mGluR-activated calcium signaling in neurons, we generated mGluR5 transgenic animals using a Thy1 promoter to drive expression in the forebrain, and one founder unexpectedly developed melanoma. To directly investigate the role of mGluR5 in melanoma formation, we generated mGluR5 transgenic lines under a melanocyte-specific promoter, tyrosinase-related protein 1. A majority of the founders showed a severe phenotype with early onset. Hyperpigmentation of the pinnae and tail could be detected as early as 3-5 d after birth for most of the mGluR5 transgene-positive mice. There was 100% penetrance in the progeny from the tyrosinase-related protein 1-mGluR5 lines generated from founders that developed melanoma. Expression of mGluR5 was detected in melanoma samples by RT-PCR, immunoblotting, and immunohistochemistry. We evaluated the expression of several cancer-related proteins in tumor samples and observed a dramatic increase in the phosphorylation of ERK, implicating ERK as a downstream effector of mGluR5 signaling in tumors. Our findings show that mGluR5-mediated glutamatergic signaling can trigger melanoma in vivo. The aggressive growth and severe phenotype make these mouse lines unique and a potentially powerful tool for therapeutic studies.

Characterization of knockin mice at the Rosa26, Tac1 and Plekhg1 loci generated by homologous recombination in oocytes.

Design and engineering of complex knockin mice has revolutionized the in vivo manipulation of genetically defined cells. Recently development of the bacterial clustered regularly interspersed short palindromic repeats (CRISPR) associated protein 9 (Cas9) system for single site cleavage of mammalian genomes has opened the way for rapid generation of knockin mice by targeting homology directed repair to selected cleavage sites. We used this approach to generate new lines of mice that will be useful for a variety of aspects of neuroscience research. These lines have been bred to homozygosity and details of the expression and function of the transgenes are reported. Two lines target the Rosa26-locus and have been engineered to allow Cre-dependent expression of the avian tva receptor, and Cre-dependent expression of a cell surface targeted spaghetti-monster carrying many copies of the "ollas-tag". Another line expresses red fluorescent protein and tva in Tac1-positive neurons; the fourth line targets FlpO expression to Plekhg1 expressing neurons, providing a powerful approach to modify gene expression in thalamic excitatory neurons.