The focus of this proposal is to elucidate the molecular mechanism of Parp1 function in epigenetic gene regulation and imprinting control, and its physiological significance. Using ES cells as a powerful tool, we will assess the progression of epigenetic reprogramming at ICRs upon Parp1 deletion and the factors involved. In a series of intercalated experiments, we will elucidate whether Parp1 is an integral component of the ICR chromatin protein complex, or whether it is the conferred post-translational modification of ICR complex members that is critical for imprint maintenance. We will also test whether the few genomic regions that are hypomethylated in Parp1-/- ES cells in addition to known ICRs demarcate yet unknown imprinting control regions that may identify novel imprinted genes. In parallel, the impact of Parp1 deficiency on imprinted gene regulation in vivo will be scrutinized. We will assess existing knockout models (of mild severity level) of Parp1, the highly related Parp2, and double mutants. The analyses will include to determine, in candidate and genome-wide approaches, the effect on DNA methylation, histone modifications (H3K9me3) and imprinted gene expression during gestation and postnatally. This will be complemented by a detailed analysis of developmental progression, postnatal and adult health, including assessment of the putative link to obesity that has been previously noted. Germ line mutants will serve to determine whether Parp1 (& Parp2) play a role in the establishment as well as the maintenance of gametic imprints, in epigenome surveillance and protection from transgenerational inheritance of epimutations. This research is pertinent to our understanding of imprinting disorders and how they might arise for example in infertility treatments. Thereby, it will identify novel avenues for potential therapeutic intervention. It also provides direct links between epigenome (dys)regulation and cancer biology, in which Parp1 is a major player.