PT - JOURNAL ARTICLE AU - Andrew M. Garrett AU - Peter J. Bosch AU - David M. Steffen AU - Leah C. Fuller AU - Charles G. Marcucci AU - Alexis A. Koch AU - Preeti Bais AU - Joshua A. Weiner AU - Robert W. Burgess TI - CRISPR/Cas9 interrogation of the mouse <em>Pcdhg</em> gene cluster reveals a crucial isoform-specific role for <em>Pcdhgc4</em> AID - 10.1101/739508 DP - 2019 Jan 01 TA - bioRxiv PG - 739508 4099 - http://biorxiv.org/content/early/2019/08/19/739508.short 4100 - http://biorxiv.org/content/early/2019/08/19/739508.full AB - 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.