Development of a floxed Gabbr2 gene allows for widespread conditional disruption of GABBR2 and recapitulates the phenotype of germline Gabbr2 knockout mice

Abstract

GABBR1 and GABBR2 are widely expressed in the brain and genetic inhibition of their function leads to widespread neurologic dysfunction and premature death in mice. Given that GABBR1 and GABBR2 heterodimerize to form a functional receptor, global knockout of GABBR1 or GABBR2 results in a similar phenotype, characterized by spontaneous epileptiform activity, hyperlocomotor activity, hyperalgesia, impaired memory and premature death. It is now known that both GABBR1 and GABBR2 are expressed in a variety of tissues outside the nervous system and that GABA-B receptors can heterodimerize with other class C GPCRs, including the extracellular calcium-sensing receptor (CaSR). Studies in vitro have demonstrated that interactions with GABBR1 and GABBR2 can alter CaSR signaling in human embryonic kidney cells and breast cancer cells. The neurologic consequences of global loss of function of GABBR1 or GABBR2 has made it difficult to study the effects of loss of GABBR function in other organs. While a conditional knockout for GABBR1 is available, the GABBR2 gene had not been "floxed". We have used CRISPR to insert loxP sites into the GABBR2 locus in mice. These mice are normal at baseline but when bred with mice expressing Cre-recombinase under the control of the ubiquitously expressed Actin gene promoter, they recapitulate the phenotype of global GABBR2 knockout mice. Phenotypic changes through the brain, including the cortex, hippocampus and cerebellum. Evidence of abnormal neuronal function, increase cell death, and changes in neuronal architecture are seen throughout the brain of CRISPR knockout mice. These mice should be useful tools to study cell type-specific loss of GABBR2 function in the brain and other organs.