%0 Journal Article %A Andrew M. Garrett %A Peter J. Bosch %A David M. Steffen %A Leah C. Fuller %A Charles G. Marcucci %A Alexis A. Koch %A Preeti Bais %A Joshua A. Weiner %A Robert W. Burgess %T CRISPR/Cas9 interrogation of the mouse Pcdhg gene cluster reveals a crucial isoform-specific role for Pcdhgc4 %D 2019 %R 10.1101/739508 %J bioRxiv %P 739508 %X The mammalian Pcdhg gene cluster encodes a family of 22 cell adhesion molecules, the gamma-Protocadherins (γ-Pcdhs), critical for neuronal survival and neural circuit formation. The extent to which isoform diversity–aγ-Pcdh hallmark–is required for their functions remains unclear. We used a CRISPR/Cas9 approach to reduce isoform diversity, targeting each Pcdhg variable exon with pooled sgRNAs to generate an allelic series of 26 mouse lines with 1 to 21 isoforms disrupted via discrete indels at guide sites and/or larger deletions/rearrangements. Analysis of 5 mutant lines indicates that postnatal viability and neuronal survival do not require isoform diversity. Surprisingly, as it is the only γ-Pcdh that cannot independently engage in homophilic trans-interactions, we find that γC4, encoded by Pcdhgc4, is the only critical isoform. Because the human orthologue is the only PCDHG gene constrained in humans, our results indicate a conserved γC4 function that likely involves distinct molecular mechanisms. %U https://www.biorxiv.org/content/biorxiv/early/2019/08/19/739508.full.pdf