The clustered gamma protocadherin PcdhγC4 isoform regulates cortical interneuron programmed cell death in the mouse cortex.

Cortical inhibitory interneurons (cINs) are born in the ventral forebrain and migrate into the cortex where they make connections with locally produced excitatory glutamatergic neurons. Cortical function critically depends on the number of cINs, which is also key to establishing the appropriate inhibitory/excitatory balance. The final number of cINs is determined during a postnatal period of programmed cell death (PCD) when ~40% of the young cINs are eliminated. Previous work shows that the loss of clustered gamma protocadherins (Pcdhgs), but not of genes in the or clusters, dramatically increased BAX-dependent cIN PCD. Here, we show that is highly expressed in cINs of the mouse cortex and that this expression increases during PCD. The sole deletion of the PcdhγC4 isoform, but not of the other 21 isoforms in the gene cluster, increased cIN PCD. Viral expression of the in cIN lacking the function of the entire cluster, rescued most of these cells from cell death. We conclude that plays a critical role in regulating the survival of cINs during their normal period of PCD. This highlights how a single isoform of the cluster, which has been linked to human neurodevelopmental disorders, is essential to adjust cIN cell numbers during cortical development.