Characterization of PARP-6 function in knock out mice and patients with developmental delay

PARP-6, a member of a family of enzymes (17 in humans) known as poly-ADP- ribose polymerases (PARPs), is a neuronally enriched PARP. While previous studies from our group show that PARP-6 is a regulator of dendrite morphogenesis in hippocampal neurons, its function in the nervous system in vivo is poorly understood. Here, we describe the generation of a PARP-6 loss-of-function mouse model for examining the function of PARP-6 during neurodevelopment in vivo. Using CRISPR-Cas9 mutagenesis, we generated a mouse line that expresses a PARP-6 truncated variant (PARP-6TR) in place of PARP-6WT. Unlike PARP-6WT, PARP-6TR is devoid of catalytic activity. Homozygous PARP-6TR do not exhibit obvious neuromorphological defects during development, but nevertheless die perinatally. This suggests that PARP-6 catalytic activity is important for postnatal survival. We also report PARP-6 mutations in six patients with several neurodevelopmental disorders, including microencephaly, intellectual disabilities, and epilepsy. The most severe mutation in PARP-6 (C563R) results in the loss of catalytic activity. Expression of the PARP-6C563R mutant in hippocampal neurons decreases dendrite morphogeneis. Taken together, these results suggest that PARP-6 is an essential gene in mice, and the loss of PARP-6 catalytic activity has detrimental effects on neuronal function in humans.