Spotlight on G-Quadruplexes: From Structure and Modulation to Physiological and Pathological Roles.

G-quadruplexes or G4s are non-canonical secondary structures of nucleic acids characterized by guanines arranged in stacked tetraplex arrays. Decades of research into these peculiar assemblies of DNA and RNA, fueled by the development and optimization of a vast array of techniques and assays, has resulted in a large amount of information regarding their structure, stability, localization, and biological significance in native systems. A plethora of articles have reported the roles of G-quadruplexes in multiple pathways across several species, ranging from gene expression regulation to RNA biogenesis and trafficking, DNA replication, and genome maintenance. Crucially, a large amount of experimental evidence has highlighted the roles of G-quadruplexes in cancer biology and other pathologies, pointing at these structurally unique guanine assemblies as amenable drug targets. Given the rapid expansion of this field of research, this review aims at summarizing all the relevant aspects of G-quadruplex biology by combining and discussing results from seminal works as well as more recent and cutting-edge experimental evidence. Additionally, the most common methodologies used to study G4s are presented to aid the reader in critically interpreting and integrating experimental data.

VID22 counteracts G-quadruplex-induced genome instability.

Genome instability is a condition characterized by the accumulation of genetic alterations and is a hallmark of cancer cells. To uncover new genes and cellular pathways affecting endogenous DNA damage and genome integrity, we exploited a Synthetic Genetic Array (SGA)-based screen in yeast. Among the positive genes, we identified VID22, reported to be involved in DNA double-strand break repair. vid22Δ cells exhibit increased levels of endogenous DNA damage, chronic DNA damage response activation and accumulate DNA aberrations in sequences displaying high probabilities of forming G-quadruplexes (G4-DNA). If not resolved, these DNA secondary structures can block the progression of both DNA and RNA polymerases and correlate with chromosome fragile sites. Vid22 binds to and protects DNA at G4-containing regions both in vitro and in vivo. Loss of VID22 causes an increase in gross chromosomal rearrangement (GCR) events dependent on G-quadruplex forming sequences. Moreover, the absence of Vid22 causes defects in the correct maintenance of G4-DNA rich elements, such as telomeres and mtDNA, and hypersensitivity to the G4-stabilizing ligand TMPyP4. We thus propose that Vid22 is directly involved in genome integrity maintenance as a novel regulator of G4 metabolism.

Safety and efficacy of transvenous mechanical lead extraction in patients with abandoned leads.

AIMS: Optimal management of redundant or malfunctioning leads is controversial. We aimed to assess safety and efficacy of mechanical transvenous lead extraction (TLE) in patients with abandoned leads. METHODS AND RESULTS: Consecutive TLE procedures performed in our centre from January 2009 to December 2017 were considered. We evaluated the safety and efficacy of mechanical TLE in patients with abandoned (Group 1) compared to non-abandoned (Group 2) leads. We analysed 1210 consecutive patients that required transvenous removal of 2343 leads. Group 1 accounted for 250 patients (21%) with a total of 617 abandoned leads (26%). Group 2 comprised 960 patients (79%) with 1726 leads (74%). The total number of leads (3.0 vs. 2.0), dwelling time of the oldest lead (108.00 months vs. 60.00 months) and infectious indications for TLE were higher in Group 1. Clinical success was achieved in 1168 patients (96.5%) with a lower rate in Group 1 (90.4% vs. 98.1%; P < 0.001). Major complications occurred in only 9 patients (0.7%), without significant differences among the two groups. The presence of one or more abandoned leads [odds ratio (OR) 3.47; 95% confidence interval (CI) 1.07-11.19; P = 0.037] and dwelling time of the oldest lead (OR 1.01 for a month; 95% CI 1.01-1.02; P < 0.001) were associated with a higher risk of clinical failure. CONCLUSION: Transvenous mechanical lead extraction is a safe procedure also in high-risk settings, as patients with abandoned leads. Success rate resulted a bit lower, especially in the presence of abandoned leads with long implantation time.

Evolutionary compromises to metabolic toxins: Ammonia and urea tolerance in Drosophila suzukii and Drosophila melanogaster.

The invasive pest Drosophila suzukii has evolved morphological and behavioural adaptations to lay eggs under the skin of fresh fruits. This results in severe damage to a wide range of small fruits. Drosophila suzukii females typically lay few eggs per fruit, preferring healthy fruits. Hence, larvae are exposed to a reduced amount of nitrogenous waste. Differently, the innocuous Drosophila melanogaster lays eggs on fermented fruits already infested by conspecifics, with larvae developing in a crowded environment with the accumulation of nitrogenous waste such as ammonia and urea. These compounds derive from nitrogen metabolism, protein degradation, and amino acids catabolism and are relatively toxic at high concentrations in an organism. The observed differences in oviposition site and larval ecological niche suggest that these species might differ in behavioural and physiological mechanisms used to cope with nitrogenous waste. We investigated how different concentrations of ammonia and urea affect oviposition and larval development in both species. Females and larvae of D. suzukii showed greater susceptibility to high concentrations of both compounds, with a dramatic decrease in the number of eggs laid and egg viability. Moreover, we tested the chemotactic response of third instar larvae to high concentrations of the compounds. Interestingly, ammonia resulted in a repulsive behaviour in respect of the control and urea groups. To better understand the pathways underlying these differences, we evaluated the effect on ornithine aminotransferase and glutathione-S-transferase, two enzymes involved in nitrogen metabolism and stress response that are expressed during larval development. Both ammonia and urea significantly reduced the expression of these enzymes in D. suzukii compared to D. melanogaster. This shows how the ecological shift of D. suzukii to fresh fruit is accompanied by less efficient detoxifying and excretory mechanisms, with important implications for evolutionary biology and applied research. Our data suggest that the ecological shift of D. suzukii to fresh fruit as oviposition substrate is accompanied by a reduced tolerance to metabolic toxins during larval development.