Noncoding RNAs (ncRNAs) have numerous roles in development and disease, and one of the prominent roles is to regulate gene expression. A vast number of circular RNAs (circRNAs) have been identified, and some have been shown to function as microRNA sponges in animal cells. Here, we report a class of circRNAs associated with RNA polymerase II in human cells. In these circRNAs, exons are circularized with introns 'retained' between exons; we term them exon-intron circRNAs or EIciRNAs. EIciRNAs predominantly localize in the nucleus, interact with U1 snRNP and promote transcription of their parental genes. Our findings reveal a new role for circRNAs in regulating gene expression in the nucleus, in which EIciRNAs enhance the expression of their parental genes in cis, and highlight a regulatory strategy for transcriptional control via specific RNA-RNA interaction between U1 snRNA and EIciRNAs.

Metal‐free polymer photocatalysts have shown great promise for photocatalytic H2O2 production via two‐electron reduction of molecular O2. The other half‐reaction, which is the two‐electron oxidation of water, still remains elusive toward H2O2 production. However, enabling this water oxidation pathway is critically important to improve the yield and maximize atom utilization efficiency. It is shown that introducing acetylene (CC) or diacetylene (CCCC) moieties into covalent triazine frameworks (CTFs) can remarkably promote photocatalytic H2O2 production. This enhancement is inherent to the incorporated carbon–carbon triple bonds which are essential in modulating the electronic structures of CTFs and suppressing charge recombinations. Furthermore, the acetylene and diacetylene moieties can significantly reduce the energy associated with OH* formation and thus enable a new two‐electron oxidation pathway toward H2O2 production. The study unveils an important reaction pathway toward photocatalytic H2O2 production, reflecting that precise control over the chemical structures of polymer photocatalysts is vital to achieve efficient solar‐to‐chemical energy conversion.

Inspired by natural photosynthesis, Z-scheme photocatalytic systems are very appealing for achieving efficient overall water splitting. Developing metal-free Z-scheme photocatalysts for overall water splitting, however, still remains challenging. The construction of polymer-based van der Waals heterostructures as metal-free Z-scheme photocatalytic systems for overall water splitting is described using aza-fused microporous polymers (CMP) and C N ultrathin nanosheets as O - and H -evolving catalysts, respectively. Although neither polymer is able to split pure water using visible light, a 2:1 stoichiometric ratio of H and O was observed when aza-CMP/C N heterostructures were used. A solar-to-hydrogen conversion efficiency of 0.23 % was determined, which could be further enhanced to 0.40 % by using graphene as the solid electron mediator to promote the interfacial charge-transfer process. This study highlights the potential of polymer photocatalysts for overall water splitting.

Converting solar energy into storable and transportable chemical fuels using artificial photosynthetic systems can provide an alternative route to the current unsustainable use of fossil fuels, addressing the worldwide energy crisis and environmental issues. Recently, semiconducting polymers have emerged as a very promising class of photocatalysts for water splitting as their electronic and structural properties can be conveniently controlled and systematically designed at a molecular level. Among the various polymer photocatalysts that are reported so far, 2D polymer nanosheets are particularly interesting and gaining more attention. The 2D planar structure offers unique features such as high surface area, abundant surface active sites, efficient charge separation, and facile formation of heterostructures. The design and synthesis of 2D polymer nanosheets have greatly advanced the research in photocatalytic overall water splitting. Here, recent advances in developing photocatalysts based on 2D polymer nanosheets for photocatalytic overall water splitting are highlighted. Specifically, the existing approaches to tune their electronic structures and surface active sites for photocatalysis are discussed. Future opportunities and challenges for developing 2D polymers for photocatalytic overall water splitting are also included.

On the basis of the duality of the shish-kebab superstructure, coil−stretch transition (CST) is well recognized as the molecular mechanism for shish-kebab formation in polymer melts, which, however, is challenged by recent results in flow-induced crystallization (FIC). In this work, we perform a real time investigation on FIC of polyethylene bimodal blends by combing a unique homemade extensional rheometer and synchrotron radiation smallangle X-ray scattering. The results show that the critical strain for shish formation decreases with increasing long chain concentration, which contradicts the role of CST but agrees well with stretched network model (SNM). Quantitative analyses indicate that the formation of shish is determined by the degree of network deformation rather than solely by strain or long chain concentration at a specific temperature. In addition, three types of shish with different stability are observed sequentially by increasing strain. On the basis of our results, strong support is given to the idea that shish formation is a kinetic process. When stretched to a critical deformation degree, the aligned segments couple with each other to form fibrillar-like type I shish, which further transform into type II shish embedded with sporadic lamellae and type III shish embedded with welldefined periodic lamellae sequentially by increasing flow intensity. Our results and the resulting conceptual model not only demonstrates that shish formation is derived from SNM but unveils its kinetic process from initial chain configuration to final stable nuclei. ■ INTRODUCTIONThe subject of flow-induced crystallization (FIC) in polymer melts is of vital importance not only in scientific research but also in industrial application. In most common scenarios flow is inevitably involved during polymer processing, which dictates subsequent morphologies and thus end-use properties of materials. 1,2 The most dramatic change in morphology associated with flow is the transition from isotropic spherulite to highly orientated shish-kebab structure with notably increased stiffness and strength. 3−7 Shish-kebab comprises of central threadlike core, namely, shish which is encircled by disklike crystals, namely kebabs. Although has been observed for several decades, the exact molecular mechanism for shish-kebab formation still remains unclear and under open debates.Two molecular mechanisms, the coil−stretch transition (CST) 8 and stretched network model (SNM) 9 are well recognized for shish-kebab formation. The CST was first proposed by de Gennes in investigating chain dynamic of polymer solution under flow. 10 Keller provided birefringent evidence for the existence of CST and attributed it to the subsequent shish-kebab formation in polymer solution. 11 Then the CST was further extended to polymer melt as the shishkebab morphology formed in melt is analogous to that in solution. 8,12 According to CST, the longest chains can be stretched to transform into shish and the rest shorter ones stay as coil state to crystallize as kebab. Soo...

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Circular RNAs (circRNAs) are a large family of newly identified transcripts, and their physiological roles and evolutionary significance require further characterization. Here, we identify circRNAs generated from a conserved reproductive gene, Boule, in species from Drosophila to humans. Flies missing circular Boule (circBoule) RNAs display decreased male fertility, and sperm of circBoule knockout mice exhibit decreased fertilization capacity, when under heat stress conditions. During spermatogenesis, fly circBoule RNAs interact with heat shock proteins (HSPs) Hsc4 and Hsp60C, and mouse circBoule RNAs in sperm interact with HSPA2. circBoule RNAs regulate levels of HSPs by promoting their ubiquitination. The interaction between HSPA2 and circBoule RNAs is conserved in human sperm, and lower levels of the human circBoule RNAs circEx3-6 and circEx2-7 are found in asthenozoospermic sperm. Our findings reveal conserved physiological functions of circBoule RNAs in metazoans and suggest that specific circRNAs may be critical modulators of male reproductive function against stresses in animals.