The Clustered Gamma Protocadherin Pcdhγc4 Isoform Regulates Cortical Interneuron Programmed Cell Death in the Mouse Cortex

Abstract

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 (Pcdhγ), 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 Pcdhγc4 isoform, but not of the other 21 isoforms in the Pcdhγ gene cluster, increased cIN cell death in mice during the normal period of programmed cell death. Viral expression of the Pcdhγc4 isoform rescued transplanted cINs lacking Pcdhγ from cell death. We conclude that Pcdhγ, specifically Pcdhγc4, 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 Pcdhγ isoforms in cortical development.

A C-terminal motif containing a PKC phosphorylation site regulates γ-Protocadherin-mediated dendrite arborization in the cerebral cortexin vivo

“…The present study, together with other recent work (Molumby et al, 2017; Garrett et al, 2019; Steffen et al, 2021; Steffen et al, 2023; Meltzer et al, 2023; Mancia Leon et al, 2024), contributes to a converging understanding of γ-Pcdh family function in which distinct roles are played by both individual isoforms and discrete protein domains. Future work aimed at identifying the full panoply of intracellular signaling partners, including both those that work with the shared constant domain and one or more VCDs, will be important to understanding how particular γ-Pcdh functions predominate depending on the neuronal or glial cell type and the stage of neural development.…”

“…Analysis of cortical dendrite arborization, however, confirms our identification of S119 phosphorylation as a key negative regulation point for the γ-Pcdhs, as both Pcdhg S/A and Pcdhg CTD homozygous mice exhibit significantly over-exuberant arbors and decreased MARCKS phosphorylation. These results delineate unique functional contributions of a particular γ-Pcdh protein domain and, along with other recent studies genetically dissecting the Pcdhg locus in vivo (Garrett et al, 2019; Mancia Leon et al, 2024; Meltzer et al, 2023; Molumby et al, 2017; Molumby et al, 2016; Steffen et al, 2021; Steffen et al, 2023), contribute to a better understanding of how this diverse protein family regulates the development of a functioning nervous system.…”

“…Conversely, a mutant mouse line in which γC4 is the only remaining functional isoform is viable and fertile (Garrett et al, 2019). This unique role for γC4 in neuronal survival has recently been confirmed for interneurons in the developing neocortex as well (Mancia Leon et al, 2024). We found that the γC3 VCD uniquely inhibits canonical Wnt signaling in non-neuronal cells through its direct interaction with the scaffolding protein Axin1 (Mah et al, 2016).…”

“…Both mutant lines are viable and fertile and exhibit no gross defects in the architecture of the brain or in cell-type specification in the cerebral cortex, indicating that the unique demonstrated role of one particular γ-Pcdh isoform, γC4, in maintaining neuronal survival (Garrett et al, 2019; Mancia Leon et al, 2024) does not require an intact C-terminus. Consistent with the predictions of our prior in vitro results (Keeler et al, 2015), we observe a lack of PKC-phosphorylated γ-Pcdh proteins in the Pcdhg S/A brain, a significant increase in the dendritic arbor complexity of layer V pyramidal neurons in both Pcdhg S/A and Pcdhg CTD , and a corresponding significant decrease in MARCKS phosphorylation in both mutant brains.…”

“…Over 20 years of functional studies have identified the γ-Pcdhs as the only cPcdhs essential for neonatal viability, and they additionally play the most important roles in several key steps in neural development (reviewed in (Peek et al, 2017)). Excessive spinal interneuron apoptosis preceding neonatal lethality in mice lacking all 22 Pcdhg genes indicates the importance of these molecules in organismal survival (Lefebvre et al, 2008; Mancia Leon et al, 2024; Prasad et al, 2008; Wang et al, 2002). In the CNS, loss of all γ-Pcdhs or disruption of normal γ-Pcdh repertoire consistently leads to disrupted neurodevelopment, including reduced dendritic arborization, loss of dendrite and axon self-avoidance, aberrant axon coalescence, and/or altered synapse formation/maturation depending upon the neuronal cell type (Garrett et al, 2012; Garrett & Weiner, 2009; Ing-Esteves et al, 2018; Kobayashi et al, 2023; Kostadinov & Sanes, 2015; Lefebvre et al, 2012; Molumby et al, 2017; Molumby et al, 2016; Mountoufaris et al, 2017; Prasad & Weiner, 2011; Steffen et al, 2021; Weiner et al, 2005).…”