The biological functions of poly(ADP-ribosyl)ation of heterogeneous nuclear ribonucleoproteins (hnRNPs) are not well understood. However, it is known that hnRNPs are involved in the regulation of alternative splicing for many genes, including the Ddc gene in Drosophila. Therefore, we first confirmed that poly(ADP-ribose) (pADPr) interacts with two Drosophila hnRNPs, Squid/hrp40 and Hrb98DE/hrp38, and that this function is regulated by Poly(ADP-ribose) Polymerase 1 (PARP1) and Poly(ADP-ribose) Glycohydrolase (PARG) in vivo. These findings then provided a basis for analyzing the role of pADPr binding to these two hnRNPs in terms of alternative splicing regulation. Our results showed that Parg null mutation does cause poly(ADP-ribosyl)ation of Squid and hrp38 protein, as well as their dissociation from active chromatin. Our data also indicated that pADPr binding to hnRNPs inhibits the RNA-binding ability of hnRNPs. Following that, we demonstrated that poly(ADP-ribosyl)ation of Squid and hrp38 proteins inhibits splicing of the intron in the Hsrω-RC transcript, but enhances splicing of the intron in the Ddc pre-mRNA. Taken together, these findings suggest that poly(ADP-ribosyl)ation regulates the interaction between hnRNPs and RNA and thus modulates the splicing pathways.

Cell growth and differentiation during developmental processes require the activation of many inducible genes. However, eukaryotic chromatin, which consists of DNA and histones, becomes a natural barrier impeding access to the functional transcription machinery. To break through the chromatin barrier, eukaryotic organisms have evolved the strategy of using Poly(ADP-ribose) polymerase 1 (PARP1) to modulate chromatin structure and initiate the steps leading to gene expression control. As a structural protein in chromatin, enzymatically silent PARP1 inhibits transcription by contributing to the condensation of chromatin, which creates a barrier against gene transcription. However, once activated by environmental stimuli and developmental signals, PARP1 can modify itself and other chromatin-associated proteins, thereby loosening chromatin to facilitate gene transcription. Here we discuss the roles of PARP1 in transcriptional control during development.

Dietary cholesterol levels control follicle stem cell proliferation in the Drosophila ovary via regulation of Hedgehog protein localization.

Impaired expression of α-defensin antimicrobial peptides and overproduction of the proinflammatory cytokine IL-1β have been associated with inflammatory bowel disease. In this study, we examine the interactions between α-defensins and IL-1β and the role of defensin deficiency in the pathogenesis of inflammatory bowel disease. It was found that matrix metalloproteinase-7-deficient (MMP-7−/−) mice, which produce procryptdins but not mature cryptdins (α-defensins) in the intestine, were more susceptible to dextran sulfate sodium-induced colitis. Furthermore, both baseline and dextran sulfate sodium-induced IL-1β production in the intestine were significantly up-regulated in MMP-7−/− mice compared with that in control C57BL/6 mice. To elucidate the molecular mechanism for the increased IL-1β production in defensin deficiency in vivo, we evaluated the effect of defensins on IL-1β posttranslational processing and release. It was found that α-defensins, including mouse Paneth cell defensins cryptdin-3 and cryptdin-4, human neutrophil defensin HNP-1, and human Paneth cell defensin HD-5, blocked the release of IL-1β from LPS-activated monocytes, whereas TNF-α expression and release were not affected. Unlike α-defensins, human β-defensins and mouse procryptdins do not have any effect on IL-1β processing and release. Thus, α-defensins may play an important role in intestinal homeostasis by controlling the production of IL-1β.

According to the histone code hypothesis, histone variants and modified histones provide binding sites for proteins that change the chromatin state to either active or repressed. Here, we identify histone variants that regulate the targeting and enzymatic activity of poly(ADP-ribose) polymerase 1 (PARP1), a chromatin regulator in higher eukaryotes. We demonstrate that PARP1 is targeted to chromatin by association with the histone H2A variant (H2Av)-the Drosophila homolog of the mammalian histone H2A variants H2Az/H2Ax-and that subsequent phosphorylation of H2Av leads to PARP1 activation. This two-step mechanism of PARP1 activation controls transcription at specific loci in a signal-dependent manner. Our study establishes the mechanism through which histone variants and changes in the histone modification code control chromatin-directed PARP1 activity and the transcriptional activation of target genes.poly(ADP-ribosyl)ation | poly(ADP-ribose) glycohydrolase | nucleosome | Hsp70