PARP1 Regulates Circular RNA Biogenesis though Control of Transcriptional Dynamics.

Circular RNAs (circRNAs) are a recently discovered class of RNAs derived from protein-coding genes that have important biological and pathological roles. They are formed through backsplicing during co-transcriptional alternative splicing; however, the unified mechanism that accounts for backsplicing decisions remains unclear. Factors that regulate the transcriptional timing and spatial organization of pre-mRNA, including RNAPII kinetics, the availability of splicing factors, and features of gene architecture, have been shown to influence backsplicing decisions. Poly (ADP-ribose) polymerase I (PARP1) regulates alternative splicing through both its presence on chromatin as well as its PARylation activity. However, no studies have investigated PARP1's possible role in regulating circRNA biogenesis. Here, we hypothesized that PARP1's role in splicing extends to circRNA biogenesis. Our results identify many unique circRNAs in PARP1 depletion and PARylation-inhibited conditions compared to the wild type. We found that while all genes producing circRNAs share gene architecture features common to circRNA host genes, genes producing circRNAs in PARP1 knockdown conditions had longer upstream introns than downstream introns, whereas flanking introns in wild type host genes were symmetrical. Interestingly, we found that the behavior of PARP1 in regulating RNAPII pausing is distinct between these two classes of host genes. We conclude that the PARP1 pausing of RNAPII works within the context of gene architecture to regulate transcriptional kinetics, and therefore circRNA biogenesis. Furthermore, this regulation of PARP1 within host genes acts to fine tune their transcriptional output with implications in gene function.

Disruption of the mouse liver epitranscriptome by long-term aroclor 1260 exposure.

Chronic environmental exposure to polychlorinated biphenyls (PCBs) is associated with non-alcoholic fatty liver disease (NAFLD) and exacerbated by a high fat diet (HFD). Here, chronic (34 wks.) exposure of low fat diet (LFD)-fed male mice to Aroclor 1260 (Ar1260), a non-dioxin-like (NDL) mixture of PCBs, resulted in steatohepatitis and NAFLD. Twelve hepatic RNA modifications were altered with Ar1260 exposure including reduced abundance of 2'-O-methyladenosine (Am) and N(6)-methyladenosine (m6A), in contrast to increased Am in the livers of HFD-fed, Ar1260-exposed mice reported previously. Differences in 13 RNA modifications between LFD- and HFD- fed mice, suggest that diet regulates the liver epitranscriptome. Integrated network analysis of epitranscriptomic modifications identified a NRF2 (Nfe2l2) pathway in the chronic, LFD, Ar1260-exposed livers and an NFATC4 (Nfatc4) pathway for LFD- vs. HFD-fed mice. Changes in protein abundance were validated. The results demonstrate that diet and Ar1260 exposure alter the liver epitranscriptome in pathways associated with NAFLD.