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Canonical G‐quadruplexes can adopt a variety of different topologies depending on the arrangement of propeller, lateral, or diagonal loops connecting the four G‐columns. A novel intramolecular G‐quadruplex structure is derived through inversion of the last G‐tract of a three‐layered parallel fold, associated with the transition of a single propeller into a lateral loop. The resulting (3+1) hybrid fold features three syn⋅anti⋅anti⋅anti G‐tetrads with a 3’‐terminal all‐syn G‐column. Although the ability of forming a duplex stem‐loop between G‐tracts seems beneficial for a propeller‐to‐lateral loop rearrangement, unmodified G‐rich sequences resist folding into the new (3+1) topology. However, refolding can be driven by the incorporation of syn‐favoring guanosine analogues into positions of the fourth G‐stretch. The presented hybrid‐type G‐quadruplex structure as determined by NMR spectroscopy may provide for an additional scaffold in quadruplex‐based technologies., Starting with a parallel‐stranded DNA G‐quadruplex, refolding into a novel (3+1) hybrid topology with a propeller‐propeller‐lateral loop architecture and an all‐syn 3’‐terminal G‐tract is reported. Although supported by additional stacking of a lateral duplex hairpin onto an outer G‐tetrad, the structural rearrangement must be enforced through the specific incorporation of syn‐favoring 8‐bromoguanosine analogues into the terminal G‐run.

A series of fluorescent ligands, which were systematically constructed from thiazole orange scaffold, was investigated for their interactions with G-quadruplex structures and antitumor activity. Among the ligands, compound 3 was identified to exhibit excellent specificity toward telomere G4-DNA over other nucleic acids. The affinity of 3-Htg24 was almost 5 times higher than that of double-stranded DNA and promoter G4-DNA. Interaction studies showed that 3 may bind to both G-tetrad and the lateral loop near the 5'-end. The intracellular colocalization with BG4 and competition studies with BRACO19 reveal that 3 may interact with G4-structures. Moreover, 3 reduces the telomere length and downregulates hTERC and hTERT mRNA expression in HeLa cells. The cytotoxicity of 3 against cancer cells (IC50 = 12.7-16.2 μM) was found to be generally higher than noncancer cells (IC50 = 52.3 μM). The findings may support that the ligand is telomere G4-DNA specific and may provide meaningful insights for anticancer drug design.

The triple-negative breast cancer (TNBC), a subtype of breast cancer which lacks of targeted therapies, exhibits a poor prognosis. It was shown recently that the PIM1 oncogene is highly related to the proliferation of TNBC cells. A quadruplex–duplex hybrid (QDH) forming sequence was recently found to exist near the transcription start site of PIM1. This structure could be an attractive target for regulation of the PIM1 gene expression and thus the treatment of TNBC. Here, we present the solution structures of two QDHs that could coexist in the human PIM1 gene. Form 1 is a three-G-tetrad-layered (3+1) G-quadruplex containing a propeller loop, a lateral loop and a stem-loop made up of three G•C Watson–Crick base pairs. On the other hand, Form 2 is an anti-parallel G-quadruplex comprising two G-tetrads and a G•C•G•C tetrad; the structure has three lateral loops with the middle stem-loop made up of two Watson-Crick G•C base pairs. These structures provide valuable information for the design of G-quadruplex-specific ligands for PIM1 transcription regulation.

Recently, the presence of i-motif structures at C-rich sequences in human cells and their regulatory functions have been demonstrated. Despite numerous steady-state studies on i-motif at neutral and slightly acidic pH, the number and nature of conformation of this biological structure are still controversial. In this work, the fluorescence lifetime of labelled molecular beacon i-motif-forming DNA sequences at different pH values is studied. The influence of the nature of bases at the lateral loops and the presence of a Watson–Crick-stabilized hairpin are studied by means of time-correlated single-photon counting technique. This allows characterizing the existence of several conformers for which the fluorophore has lifetimes ranging from picosecond to nanosecond. The information on the existence of different i-motif structures at different pH values has been obtained by the combination of classical global decay fitting of fluorescence traces, which provides lifetimes associated with the events defined by the decay of each sequence and multivariate analysis, such as principal component analysis or multivariate curve resolution based on alternating least squares. Multivariate analysis, which is seldom used for this kind of data, was crucial to explore similarities and differences of behaviour amongst the different DNA sequences and to model the presence and identity of the conformations involved in the pH range of interest. The results point that, for i-motif, the intrachain contact formation and its dissociation show lifetimes ten times faster than for the open form of DNA sequences. They also highlight that the presence of more than one i-motif species for certain DNA sequences according to the length of the sequence and the composition of the bases in the lateral loop., Funding from Spanish government [CTQ2014-61758-EXP, CTQ2014-52588-R, CTQ2015-66254-C2-2-P]; Autonomous Catalan government [2017SGR114]. Funding for open access charge: University of Bracelona [CTQ2015-66254-C2-2-P] and Université de Lille, LASIR CNRS.

Context. Prominence eruptions provide key observations to understand the launch of coronal mass ejections as their cold plasma traces a part of the unstable magnetic configuration. Aims. We select a well observed case to derive observational constraints for eruption models. Methods. We analyze the prominence eruption and loop expansion and contraction observed on 02 March 2015 associated with a GOES M3.7 class flare (SOL2015-03-02T15:27) using the data from Atmospheric Imaging Assembly (AIA) and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). We study the prominence eruption and the evolution of loops using the time-distance techniques. Results. The source region is a decaying bipolar active region where magnetic flux cancellation is present for several days before the eruption. AIA observations locate the erupting prominence within a flux rope viewed along its local axis direction. We identify and quantify the motion of loops in contraction and expansion located on the side of the erupting flux rope. Finally, RHESSI hard X-ray observations identify the loop top and two foot-point sources. Conclusions. Both AIA and RHESSI observations support the standard model of eruptive flares. The contraction occurs 19 minutes after the start of the prominence eruption indicating that this contraction is not associated with the eruption driver. Rather, this prominence eruption is compatible with an unstable flux rope where the contraction and expansion of the lateral loop is the consequence of a side vortex developing after the flux rope is launched., Comment: 16 pages, 9 figures, 1 table, and appendix

A (3+1)-hybrid-type G-quadruplex was substituted within its central tetrad by a single 2'-fluoro-modified guanosine. Driven by the anti-favoring nucleoside analogue, a novel quadruplex fold with inversion of a single G-tract and conversion of a propeller loop into a lateral loop emerges. In addition, scalar couplings across hydrogen bonds demonstrate the formation of intra- and inter-residual F⋅⋅⋅H8-C8 pseudo-hydrogen bonds within the modified quadruplexes. Alternative folding can be rationalized by the impact of fluorine on intermediate species on the basis of a kinetic partitioning mechanism. Apparently, chemical or other environmental perturbations are able to redirect folding of a quadruplex, possibly modulating its regulatory role in physiological processes.

We describe a patient who underwent arthroscopic pullout fixation for a posterior cruciate ligament (PCL) avulsion fracture. A 46-year-old female, injured in a fall while riding a motorcycle, was diagnosed with a right knee PCL tibial attachment avulsion fracture and underwent arthroscopic osteosynthesis. A Kirschner wire was drilled to a point just medial to the medial border of the anterior tibial bony bed. A suture wire was folded into a loop and introduced into the posteromedial compartment via the bone tunnel. A fixation thread was inserted from the posteromedial portal, through the medial and lateral loop wires, and into the posteromedial compartment. The lateral and medial loop wires attached to the thread were pulled to the outside, and the thread was fixed onto the tibia. Three months post-surgery, she returned to her job. This procedure represents a minimally invasive method of treating avulsion fractures of the tibial attachment of the PCL.

Lampbrush chromosomes are giant, transcriptionally active, meiotic chromosomes found in oocytes of all vertebrates with the exception of mammals. Lampbrush chromosomes offer a convenient tool for cytogenetic mapping and, in particular, have been instrumental in mapping genes and linkage groups on chicken (GGA) chromosomes. Whereas cytogenetic maps of macrochromosome GGA1-10 and microchromosome GGA11-16 lampbrush bivalents have been established, identification and description of smaller microchromosome bivalents are still missing. In this work, we used specific FISH probes for the identification of 12 chicken lampbrush chromosomes formed by GGA17-28. Our observations on chromomere and lateral loop arrangement and chiasma position allowed us to construct the respective cytogenetic maps for these microchromosomes. For the 10 smallest chicken microchromosomes, GGA29-38, no individual molecular tags are available, yet they can be collectively marked using the PO41 repeat. The reported results contribute to building of working cytogenetic maps of the chicken karyotype. (C) 2017 S.Karger AG, BaselKeywords

Hypersonic glide vehicles have strong lateral mobility which will lead to great bank-angle in flight. Hence, great longitudinal and lateral loop coupling will greatly increase the difficulty of guidance. Since traditional decoupling guidance strategy is difficult to adapt to this situation; to solve this problem, this paper introduces a concept of virtual displacement from analytical mechanics and designs virtual displacement guidance method for hypersonic glide vehicle, based on the small control changes' impact on the whole trajectory. In every guidance period, virtual displacement guidance method predicts the vehicle's landing point, searching the optimal bank-angle and angle of attack successively to correct the error. Simulation results show that virtual displacement is able to achieve higher guidance accuracy in both standard and uncertain conditions than traditional methods. In addition, lateral error corridor introduced can restrain the control's chatter phenomenon.

Platelet-derived growth factor receptor beta (PDGFR-β) is a cell-surface-receptor tyrosine kinase implicated in platelet-derived growth factor (PDGF) signaling pathways, and overexpression of PDGFR-β is associated with tumor growth, angiogenesis, and migration, making PDGFR-β an attractive target for cancer therapy. The formation of DNA G-quadruplexes in the GC-rich nuclease hypersensitivity element of the human PDGFR-β gene promoter has been found to inhibit PDGFR-β transcriptional activity. We previously determined the major G-quadruplex structure formed in the PDGFR-β promoter using a 22-mer sequence of pu22m1, which adopts a folding pattern containing a unique broken G-strand with the 3' tetrad-guanine coming from a distant site connected by a five nucleotide lateral loop. However, extension of the 3' end flanking segment of pu22m1 results in destabilization of the G-quadruplex, suggesting that this structure may be unstable in vivo. Recently, it has been reported that a unique type of intramolecular G-vacancy-bearing G-quadruplex (GVBQ) can be formed with three G3 tracts and one G2 tract and has an incomplete G-tetrad with a G-vacancy. A guanine derivative, such as GMP or GTP, can fill the G-vacancy with Hoogsteen hydrogen bonding and complete the G-tetrad, resulting in G-quadruplex stabilization. The unique broken-strand structure of PDGFR-β pu22m1 suggests a possibility of the formation of a GVBQ structure in this sequence, which can be completed and stabilized by guanine and guanine derivatives. To test this hypothesis, we examined the formation and stability of G-quadruplex formed in pu22m1 variants and the potential of guanine derivatives to fill in the incomplete G-tetrad and stabilize the overall G-quadruplex, using nuclear magnetic resonance spectroscopy, circular dichroism spectroscopy and DMS footprinting experiments. Our results showed that a GVBQ could form in in the PDGFR-β promoter sequence and that dGMP could insert and complete the incomplete G-tetrad to induce the formation of a stable and well-defined dGMP-fill-in-GVBQ in potassium solution. In addition, we discovered two natural plant alkaloids, berberine and chelerythrine, which could stabilize this dGMP-fill-in-GVBQ, with an increase in melting temperature by more than 10 °C. Therefore, it appears that dGMP could interact and stabilize the broken-stranded PDGFR-β promoter G-quadruplex, which may play a role in PDGFR-β transcriptional regulation. Elevated levels of guanine and guanine derivatives/metabolites are found in tumor cells, suggesting that the GVBQs may play important regulatory roles in tumor cell pathological processes, such as PDGFR-β transcriptional regulation. Furthermore, our results suggest that this unique dGMP-fill-in G-quadruplex in the PDGFR-β promoter may serve as a novel anticancer drug target for modulating PDGFR-β gene regulation. Citation Format: Kaibo Wang, Clement Lin, Guanhui Wu, Danzhou Yang. A dGMP fill-in G-quadruplex forms in the PDGFR-β promoter that serves as a unique target for drug design [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 687.

Overexpression of platelet-derived growth factor receptor β (PDGFR-β) is associated with multiple cancers, making PDGFR-β an attractive target for anticancer drugs. Few strategies other than molecular targeting of the PDGFR-β protein or its cognate ligand have been reported for developing inhibitors for the PDGFR-β signaling pathway. DNA G-quadruplexes (G4s) formed in the GC-rich nuclease hypersensitivity element of the human PDGFR-β gene promoter have been found to inhibit PDGFR-β transcriptional activity, and stabilization of these G4s by small-molecule compounds could serve as a mechanism for cancer therapeutics. We have shown that the major G4 formed in the PDGFR-β promoter is from the central four G-runs, adopting an intramolecular parallel-stranded structure with a broken G-strand and contains three 1-nucleotide (nt) chain-reversal loops and one lateral loop. The novel folding of the PDGFR-β G4 highlights the inherent stability of the 1-nt loops in parallel-stranded G4 structures. Elucidating the structure of the major PDGFR-β promoter G4 is important for designing small-molecule drugs to specifically target this structure to inhibit gene transcription. Using nuclear magnetic resonance (NMR) spectroscopy, we have determined the potassium solution structure of this major G4 formed in the PDGFR-β promoter. Our structure showed a unique 3’ capping structure involving three guanine nucleotides in the lateral loop. This novel capping structure is determined by the specific loop sequence as well as the broken-stranded PDGFR-β G4 folding pattern. The unique 3’ capping structure could be specifically recognized by proteins and small molecule ligands. Unrestrained molecular dynamic calculations showed that this major PDGFR-β G4 and its 3’ capping structure are stable in aqueous environment on the ns time-scale. We also investigated the binding of small-molecules to the PDGFR-β G4 using a combination of NMR, circular dichroism (CD), and fluorescence based methods to identify compounds that can selectively bind the PDGFR-β G4 over other classic parallel-stranded G-quadruplexes, such as the c-MYC promoter G4. Our study demonstrates the structural diversity in promoter G4s which may enable specific recognition and the modulation of gene expression by small-molecule drugs. Citation Format: Clement Lin, Prashansa Agrawal, Yuwei Chen, Salil Kalarn, Nanjie Deng, Laurence Hurley, Danzhou Yang. Molecular structure of the major G-quadruplex formed in the PDGFR-β promoter nuclease hypersensitivity element and its binding with small molecules. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3090.