Abstract
PARP1 (ARTD1) and Tankyrases (TNKS1/TNKS2; PARP5a/5b) are poly-ADP-ribose polymerases (PARPs) with catalytic and non-catalytic functions that regulate both the genome and proteome during zygotic genome activation (ZGA), totipotent, and pluripotent embryonic stages. Here, we show that primed, conventional human pluripotent stem cells (hPSC) cultured continuously under non-specific TNKS1/TNKS2/PARP1-inhibited chemical naive reversion conditions underwent epigenetic reprogramming to clonal blastomere-like stem cells. TIRN stem cells concurrently expressed hundreds of gene targets of the ZGA-priming pioneer factor DUX4, as well as a panoply of four-cell (4C)-specific (e.g., TPRXL, HOX clusters), eight-cell (8C)-specific (e.g., DUXA, GSC, GATA6), primitive endoderm-specific (e.g., GATA4, SOX17), trophectoderm-specific (e.g., CDX2, TFAP2C), and naive epiblast-specific (e.g., DNMT3L, NANOG, POU5F1(OCT4)) factors; all in a hybrid, combinatorial single-cell manner. Mapping of proteomic and single-cell expressions of TIRN cells against human preimplantation embryo references identified them as relatively homogenous 4C-8C stage populations. Injection of TIRN cells into murine 8C-16C-staged embryos resulted in efficient totipotent-like single cell contributions of human cells to both extra-embryonic (trophectoderm, placenta) and embryonic (neural, fetal liver, hematopoietic) lineages in human-murine blastocyst and fetal chimeras. Pairing of proteome with ubiquitinome analyses of TIRN cells revealed a global shutdown of ADP-ribosylation, and a perturbed TNKS/PARP1 equilibrium which not only impacted the protein levels of hundreds of TNKS/PARP1 substrates via a rewiring of the ubiquitin-proteosome system (UPS), but also de-repressed expression of hundreds of developmental genes associated with PARP1 suppression. ChIP-Seq analysis of core NANOG-SOX2-OCT4 (NSO) pluripotency factors in TIRN cells identified reprogrammed DUX4-accessible distal and cis-regulatory enhancer regions that were co-bound by PARP1 (NSOP). These NSOP enhancer regions possessed co-binding motifs for hundreds of the same ZGA-associated, embryonic, and extraembryonic lineage-specifying pioneer factors (e.g., HOX, FOX, GATA, SOX, TBX, CDX families) that were concurrently co-expressed in TIRN cells; suggesting that PARP1 and DUX4 cooperate with NSO pluripotency core factors to regulate the epigenetic plasticity of a human totipotency program. These findings provide the first demonstration that global, proteome-wide perturbations of post-translational modifications (i.e., ADP-ribosylation, ubiquitination) can regulate epigenetic reprogramming during human embryogenesis. Totipotent TIRN stem cells will provide a valuable cell culture model for studying the proteogenomic regulation of lineage specification from human blastomere stages and may facilitate the efficient generation of human organs in interspecies chimeras.