Cortical function critically depends on inhibitory/excitatory balance. Cortical inhibitory interneurons (cINs) are born in the ventral forebrain and migrate into cortex, where their numbers are adjusted by programmed cell death. Previously, we showed that loss of clustered gamma protocadherins (Pcdh{gamma}), but not of genes in the alpha or beta clusters, increased dramatically cIN BAX-dependent cell death in mice. Here we show that the sole deletion of the Pcdh{gamma}c4 isoform, but not of the other 21 isoforms in the Pcdh{gamma} gene cluster, increased cIN cell death in mice during the normal period of programmed cell death. Viral expression of the Pcdh{gamma}c4 isoform rescued transplanted cINs lacking Pcdh{gamma} from cell death. We conclude that Pcdh{gamma}, specifically Pcdh{gamma}c4, plays a critical role in regulating the survival of cINs during their normal period of cell death. This demonstrates a novel specificity in the role of Pcdh{gamma} isoforms in cortical development.
