Candidats médicaments et sondes pour les structures secondaires des acides nucléiques

Publications de l’équipe

Année de publication : 2020

Rahima Chennoufi, Ngoc-Duong Trinh, Françoise Simon, Guillaume Bordeau, Delphine Naud-Martin, Albert Moussaron, Bertrand Cinquin, Houcine Bougherara, Béatrice Rambaud, Patrick Tauc, Céline Frochot, Marie-Paule Teulade-Fichou, Florence Mahuteau-Betzer & Eric Deprez (2020 Apr 23)

Interplay between cellular uptake, intracellular localization and the cell death mechanism in triphenylamine-mediated photoinduced cell death

Scientific Reports : 10 : 6881 : DOI : 10.1038/s41598-020-63991-9 En savoir plus

Triphenylamines (TPAs) were previously shown to trigger cell death under prolonged one- or two-photon illumination. Their initial subcellular localization, before prolonged illumination, is exclusively cytoplasmic and they translocate to the nucleus upon photoactivation. However, depending on their structure, they display significant differences in terms of precise initial localization and subsequent photoinduced cell death mechanism. Here, we investigated the structural features of TPAs that influence cell death by studying a series of molecules differing by the number and chemical nature of vinyl branches. All compounds triggered cell death upon one-photon excitation, however to different extents, the nature of the electron acceptor group being determinant for the overall cell death efficiency. Photobleaching susceptibility was also an important parameter for discriminating efficient/inefficient compounds in two-photon experiments. Furthermore, the number of branches, but not their chemical nature, was crucial for determining the cellular uptake mechanism of TPAs and their intracellular fate. The uptake of all TPAs is an active endocytic process but two- and three-branch compounds are taken up via distinct endocytosis pathways, clathrin-dependent or -independent (predominantly caveolae-dependent), respectively. Two-branch TPAs preferentially target mitochondria and photoinduce both apoptosis and a proper necrotic process, whereas three-branch TPAs preferentially target late endosomes and photoinduce apoptosis only.

Ehlen A., Martin C., Miron S., Julien M., Theillet F.X., Boucherit V., Ropars V., Duchambon P., El Marjou A., Zinn Justin S., Carreira A. (2020 Apr 14)

Proper chromosome alignment depends on BRCA2 phosphorylation by PLK1

Nature Communications : 11 : 1819 : DOI : 10.1038/s41467-020-15689-9 En savoir plus

The BRCA2 tumor suppressor protein is involved in the maintenance of genome integrity through its role in homologous recombination. In mitosis, BRCA2 is phosphorylated by Polo-like kinase 1 (PLK1). Here we describe how this phosphorylation contributes to the control of mitosis. We identify a conserved phosphorylation site at T207 of BRCA2 that constitutes a bona fide docking site for PLK1 and is phosphorylated in mitotic cells. We show that BRCA2 bound to PLK1 forms a complex with the phosphatase PP2A and phosphorylated-BUBR1. Reducing BRCA2 binding to PLK1, as observed in BRCA2 breast cancer variants S206C and T207A, alters the tetrameric complex resulting in unstable kinetochore-microtubule interactions, misaligned chromosomes, faulty chromosome segregation and aneuploidy. We thus reveal a role of BRCA2 in the alignment of chromosomes, distinct from its DNA repair function, with important consequences on chromosome stability. These findings may explain in part the aneuploidy observed in BRCA2-mutated tumors.

Abhijit Saha, Patricia Duchambon, Vanessa Masson, Damarys Loew, Sophie Bombard, Marie-Paule Teulade-Fichou (2020 Mar 20)

Nucleolin Discriminates Drastically between Long-Loop and Short-Loop Quadruplexes.

Biochemistry : 59 : 1261-1272 : DOI : 10.1021/acs.biochem.9b01094 En savoir plus

We investigate herein the interaction between nucleolin (NCL) and a set of G4 sequences derived from the CEB25 human minisatellite that adopt a parallel topology while differing in the length of the central loop (from nine nucleotides to one nucleotide). It is revealed that NCL strongly binds to long-loop (five to nine nucleotides) G4 while interacting weakly with the shorter variants (loop with fewer than three nucleotides). Photo-cross-linking experiments using 5-bromo-2′-deoxyuridine (BrU)-modified sequences further confirmed the loop-length dependency, thereby indicating that the WT-CEB25-L191 (nine-nucleotide loop) is the best G4 substrate. Quantitative proteomic analysis (LC-MS/MS) of the product(s) obtained by photo-cross-linking NCL to this sequence enabled the identification of one contact site corresponding to a 15-amino acid fragment located in helix α2 of RNA binding domain 2 (RBD2), which sheds light on the role of this structural element in G4-loop recognition. Then, the ability of a panel of benchmark G4 ligands to prevent the NCL-G4 interaction was explored. It was found that only the most potent ligand PhenDC3 can inhibit NCL binding, thereby suggesting that the terminal guanine quartet is also a strong determinant of G4 recognition, putatively through interaction with the RGG domain. This study describes the molecular mechanism by which NCL recognizes G4-containing long loops and leads to the proposal of a model implying a concerted action of RBD2 and RGG domains to achieve specific G4 recognition via a dual loop-quartet interaction.

Nucleolin Discriminates Drastically between Long-Loop and Short-Loop Quadruplexes

Paudel B.P., Moye A.L., Assi H.A., El-Khoury R., Cohen S.B., Birrento M.L., Samosorn S., Intharapichai K., Tomlinson C.G., Teulade-Fichou M.P., Gonz'alez C., Beck J.L., Damha M.J., van Oijen A.M., Bryan T.M. (2020 Feb 27)

A mechanism for the extension and unfolding of parallel telomeric G-quadruplexes by human telomerase at single-molecule resolution

bioRxiv : DOI : 10.1101/2020.02.26.965269 En savoir plus

Telomeric G-quadruplexes (G4) were long believed to form a protective structure at telomeres, preventing their extension by the ribonucleoprotein telomerase. Contrary to this belief, we have previously demonstrated that parallel-stranded conformations of telomeric G4 can be extended by human and ciliate telomerase. However, a mechanistic understanding of the interaction of telomerase with structured DNA remained elusive. Here, we use single-molecule fluorescence resonance energy transfer (smFRET) microscopy and bulk-phase enzymology to propose a mechanism for the resolution and extension of parallel G4 by telomerase. Binding is initiated by the RNA template of telomerase interacting with the G-quadruplex; nucleotide addition then proceeds to the end of the RNA template. It is only through the large conformational change of translocation following synthesis that the G-quadruplex structure is completely unfolded to a linear product. Surprisingly, parallel G4 stabilization with either small molecule ligands or by chemical modification does not always inhibit G4 unfolding and extension by telomerase. These data reveal that telomerase is a parallel G-quadruplex resolvase.


Année de publication : 2019

Stéphanie Lemaître, Florent Poyer, Paul Fréneaux, Sophie Leboucher, François Doz, Nathalie Cassoux, Carole D Thomas (2019 Dec 25)

Low retinal toxicity of intravitreal carboplatin associated with good retinal tumor control in transgenic murine retinoblastoma.

Clinical & experimental ophthalmology : DOI : 10.1111/ceo.13711 En savoir plus


Retinoblastoma is a rare intraocular malignancy in children. Current treatments have many adverse effects. New therapeutic approaches like intravitreal injections of chemotherapies are currently being developed but their toxicities need to be evaluated on animal models. This study compares the efficacy and toxicity of intravitreal melphalan, topotecan and carboplatin, alone or in combination (sequential administration), in the LHBetaTag retinoblastoma mice.


Mice were divided into 9 groups: control, carboplatin 1.5 and 4μg, melphalan 0.1 and 1μg, topotecan 0.1 and 1μg, carboplatin 4μg/ topotecan 0.1μg and melphalan 1μg/ topotecan 0.1μg. The follow‐up was performed using fundus imaging and optical coherence tomography combined with histopathological analysis. Absence of tumor and presence of calcified tumors were the criteria for therapeutic response assessment. Ocular complications were assessed after 4 weekly injections. Retinal toxicity was defined by the decrease of retinal thickness and of the number of retinal layers.


Topotecan was inactive on retinal tumors. Melphalan (1μg) led to a complete tumor control in 91.7% of eyes. Carboplatin strongly decreased the tumor burden (85.7‐93.8% of eyes without retinal tumor). The intravitreal injection itself led to ocular complications (25% of media opacities and 45.7% of retinal detachment). Only melphalan at 1μg showed a strong retinal toxicity. The two combinations showed a good efficacy in reducing the number of eyes with retinal tumors with a reduced retinal toxicity.


This preclinical study suggests that intravitreal injection of carboplatin has a low toxicity and could be evaluated in clinical practice to treat patients suffering from retinoblastoma.

Nathalie Grandin, Bruno Pereira, Camille Cohen, Pauline Billard, Caroline Dehais, Catherine Carpentier, Ahmed Idbaih, Franck Bielle, François Ducray, Dominique Figarella-Branger, Jean-Yves Delattre, Marc Sanson, Patrick Lomonte, Delphine Poncet, Pierre Verrelle, Michel Charbonneau, (2019 Nov 11)

The level of activity of the alternative lengthening of telomeres correlates with patient age in IDH-mutant ATRX-loss-of-expression anaplastic astrocytomas.

Acta neuropathologica communications : 7 : 175 : DOI : 10.1186/s40478-019-0833-0 En savoir plus

All cancer cells need to maintain functional telomeres to sustain continuous cell division and proliferation. In human diffuse gliomas, functional telomeres are maintained due either to reactivation of telomerase expression, the main pathway in most cancer types, or to activation of a mechanism called the alternative lengthening of telomeres (ALT). The presence of IDH1/2 mutations (IDH-mutant) together with loss of ATRX expression (ATRX-lost) are frequently associated with ALT in diffuse gliomas. However, detection of ALT, and a fortiori its quantification, are rarely, if ever, measured in neuropathology laboratories. We measured the level of ALT activity using the previously described quantitative « C-circle » assay and analyzed it in a well characterized cohort of 104 IDH-mutant and ATRX-lost adult diffuse gliomas. We report that in IDH-mutant ATRX-lost anaplastic astrocytomas, the intensity of ALT was inversely correlated with age (p < 0.001), the younger the patient, the higher the intensity of ALT. Strikingly, glioblastomas having progressed from anaplastic astrocytomas did not exhibit this correlation. ALT activity level in the tumor did not depend on telomere length in healthy tissue cells from the same patient. In summary, we have uncovered the existence, in anaplastic astrocytomas but not in glioblastomas with the same IDH and ATRX mutations, of a correlation between patient age and the level of activity of ALT, a telomerase-independent pathway of telomere maintenance.

Priyanka Toshniwal, Michelle Nguyen, Aurore Guédin, Helena Viola, Diwei Ho, Yongeun Kim, Uditi Bhatt, Charles Bond, Livia Hool, Laurence H Hurley, Jean-Louis Mergny, Mark Fear, Fiona Wood, K Swaminathan Iyer, Nicole M Smith (2019 Nov 2)

TGF-β-induced fibrotic stress increases G-quadruplex formation in human fibroblasts.

FEBS letters : 593 : 3149-3161 : DOI : 10.1002/1873-3468.13658 En savoir plus

Scar formation after wound healing is a major medical problem. A better understanding of the dynamic nuclear architecture of the genome during wound healing could provide insights into the underlying pathophysiology and enable novel therapeutic strategies. Here, we demonstrate that TGF-β- induced fibrotic stress increases formation of the dynamic secondary DNA structures called G-quadruplexes in skin fibroblasts, which is coincident with increased expression of collagen 1. This G-quadruplex formation is attenuated by a small molecule inhibitor of intracellular Ca influx and an anti-fibrotic compound. In addition, we identify G-quadruplex-forming sequences in the promoter region of COL1A1, which encodes collagen 1, and confirm their ability to form G-quadruplex structures under physiologically relevant conditions. Our findings reveal a link between G-quadruplexes and scar formation that may lead to novel therapeutic interventions.

Chen J., Zhang Y., Cheng M., Mergny J.L., Lin Q., Zhou J., Ju H. (2019 Nov 1)

Highly active G-quadruplex/hemin DNAzyme for sensitive colorimetric determination of lead(II)

Microchimica Acta : 186 : 786 : DOI : 10.1007/s00604-019-3950-3 En savoir plus

A UV-vis, CD, and differential pulse voltammetric study was performed on the deactivation of the activity of parallel G-quadruplex/hemin DNAzymes (G4 DNAzymes) by Pb(II). The G4 DNAzyme carries a d[TC] sequence at its 3extasciiacutex end and is stabilized by potassium(I). On addition of Pb(II), the K(I) ions in the parallel G4 are replaced by Pb(II) to keep the parallel topology. Intruded Pb(II) decrease the affinity between the topology and hemin, this leads to a decrease of DNAzyme activity for catalyzing the oxidation of 2,2extasciiacutex-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) by hydrogen peroxide to form a green dye with an absorption maximum at 420 nm. The assay does not use any amplification, and has a linear response in the 0.01 to 10 muM Pb(II) concentration range and a 7.1 nM limit of detection. The method was successfully applied to the analysis of spiked water samples.

Franck Court, Elisa Le Boiteux, Anne Fogli, Mélanie Müller-Barthélémy, Catherine Vaurs-Barrière, Emmanuel Chautard, Bruno Pereira, Julian Biau, Jean-Louis Kemeny, Toufic Khalil, Lucie Karayan-Tapon, Pierre Verrelle, Philippe Arnaud (2019 Sep 20)

Transcriptional alterations in glioma result primarily from DNA methylation-independent mechanisms.

Genome research : 29 : 1605-1621 : DOI : 10.1101/gr.249219.119 En savoir plus

In cancer cells, aberrant DNA methylation is commonly associated with transcriptional alterations, including silencing of tumor suppressor genes. However, multiple epigenetic mechanisms, including polycomb repressive marks, contribute to gene deregulation in cancer. To dissect the relative contribution of DNA methylation-dependent and -independent mechanisms to transcriptional alterations at CpG island/promoter-associated genes in cancer, we studied 70 samples of adult glioma, a widespread type of brain tumor, classified according to their isocitrate dehydrogenase (IDH1) mutation status. We found that most transcriptional alterations in tumor samples were DNA methylation-independent. Instead, altered histone H3 trimethylation at lysine 27 (H3K27me3) was the predominant molecular defect at deregulated genes. Our results also suggest that the presence of a bivalent chromatin signature at CpG island promoters in stem cells predisposes not only to hypermethylation, as widely documented, but more generally to all types of transcriptional alterations in transformed cells. In addition, the gene expression strength in healthy brain cells influences the choice between DNA methylation- and H3K27me3-associated silencing in glioma. Highly expressed genes were more likely to be repressed by H3K27me3 than by DNA methylation. Our findings support a model in which altered H3K27me3 dynamics, more specifically defects in the interplay between polycomb protein complexes and the brain-specific transcriptional machinery, is the main cause of transcriptional alteration in glioma cells. Our study provides the first comprehensive description of epigenetic changes in glioma and their relative contribution to transcriptional changes. It may be useful for the design of drugs targeting cancer-related epigenetic defects.

Angrand G., Quillévéré A., Loaëc N., Daskalogianni C., Granzhan A., Teulade-Fichou M.P., Fahraeus R., Prado Martins R., Blondel M. (2019 Sep 1)

Sneaking Out for Happy Hour: Yeast-Based Approaches to Explore and Modulate Immune Response and Immune Evasion

Genes : 10 : 667-689 : DOI : 10.3390/genes10090667 En savoir plus

Many pathogens (virus, bacteria, fungi, or parasites) have developed a wide variety of mechanisms to evade their host immune system. The budding yeast Saccharomyces cerevisiae has successfully been used to decipher some of these immune evasion strategies. This includes the cis-acting mechanism that limits the expression of the oncogenic Epstein–Barr virus (EBV)-encoded EBNA1 and thus of antigenic peptides derived from this essential but highly antigenic viral protein. Studies based on budding yeast have also revealed the molecular bases of epigenetic switching or recombination underlying the silencing of all except one members of extended families of genes that encode closely related and highly antigenic surface proteins. This mechanism is exploited by several parasites (that include pathogens such as Plasmodium, Trypanosoma, Candida, or Pneumocystis) to alternate their surface antigens, thereby evading the immune system. Yeast can itself be a pathogen, and pathogenic fungi such as Candida albicans, which is phylogenetically very close to S. cerevisiae, have developed stealthiness strategies that include changes in their cell wall composition, or epitope-masking, to control production or exposure of highly antigenic but essential polysaccharides in their cell wall. Finally, due to the high antigenicity of its cell wall, yeast has been opportunistically exploited to create adjuvants and vectors for vaccination.

Michaela Krafcikova, Simon Dzatko, Coralie Caron, Anton Granzhan, Radovan Fiala, Tomas Loja, Marie-Paule Teulade-Fichou, Tomas Fessl, Robert Hänsel-Hertsch, Jean-Louis Mergny, Silvie Foldynova-Trantirkova, Lukas Trantirek (2019 Aug 9)

Monitoring DNA–Ligand Interactions in Living Human Cells Using NMR Spectroscopy

Journal of the American Chemical Society : 141 : 13281-13285 : DOI : 10.1021/jacs.9b03031 En savoir plus

Studies on DNA–ligand interactions in the cellular environment are problematic due to the lack of suitable biophysical tools. To address this need, we developed an in-cell NMR-based approach for monitoring DNA–ligand interactions inside the nuclei of living human cells. Our method relies on the acquisition of NMR data from cells electroporated with preformed DNA–ligand complexes. The impact of the intracellular environment on the integrity of the complexes is assessed based on in-cell NMR signals from unbound and ligand-bound forms of a given DNA target. This technique was tested on complexes of two model DNA fragments and four ligands, namely, a representative DNA minor-groove binder (netropsin) and ligands binding DNA base-pairing defects (naphthalenophanes). In the latter case, we demonstrate that two of the three in vitro-validated ligands retain their ability to form stable interactions with their model target DNA in cellulo, whereas the third one loses this ability due to off-target interactions with genomic DNA and cellular metabolites. Collectively, our data suggest that direct evaluation of the behavior of drug-like molecules in the intracellular environment provides important insights into the development of DNA-binding ligands with desirable biological activity and minimal side effects resulting from off-target binding.

Monitoring DNA–Ligand Interactions in Living Human Cells Using NMR Spectroscopy

Xiao Xie, Michela Zuffo, Marie-Paule Teulade-Fichou, Anton Granzhan (2019 Aug 6)

Identification of optimal fluorescent probes for G-quadruplex nucleic acids through systematic exploration of mono- and distyryl dye libraries

Beilstein Journal of Organic Chemistry : 15 : 1872–1889 : DOI : 10.3762/bjoc.15.183 En savoir plus

A library of 52 distyryl and 9 mono-styryl cationic dyes was synthesized and investigated with respect to their optical properties, propensity to aggregation in aqueous medium, and capacity to serve as fluorescence “light-up” probes for G-quadruplex (G4) DNA and RNA structures. Among the 61 compounds, 57 dyes showed preferential enhancement of fluorescence intensity in the presence of one or another G4-DNA or RNA structure, while no dye displayed preferential response to double-stranded DNA or single-stranded RNA analytes employed at equivalent nucleotide concentration. Thus, preferential fluorimetric response towards G4 structures appears to be a common feature of mono- and distyryl dyes, including long-known mono-styryl dyes used as mitochondrial probes or protein stains. However, the magnitude of the G4-induced “light-up” effect varies drastically, as a function of both the molecular structure of the dyes and the nature or topology of G4 analytes. Although our results do not allow to formulate comprehensive structure–properties relationships, we identified several structural motifs, such as indole- or pyrrole-substituted distyryl dyes, as well as simple mono-stryryl dyes such as DASPMI [2-(4-(dimethylamino)styryl)-1-methylpyridinium iodide] or its 4-isomer, as optimal fluorescent light-up probes characterized by high fluorimetric response (I/I0 of up to 550-fold), excellent selectivity with respect to double-stranded DNA or single-stranded RNA controls, high quantum yield in the presence of G4 analytes (up to 0.32), large Stokes shift (up to 150 nm) and, in certain cases, structural selectivity with respect to one or another G4 folding topology. These dyes can be considered as promising G4-responsive sensors for in vitro or imaging applications. As a possible application, we implemented a simple two-dye fluorimetric assay allowing rapid topological classification of G4-DNA structures.

Identification of optimal fluorescent probes for G-quadruplex nucleic acids

Birzu C., Hillairet A., Giry M., Grandin N., Verrelle P., Mokhtari K., Marie Y., Hoang-Xuan K., Delattre J., Idbaih A., Charbonneau M., Sanson M., Alentorn A. (2019 Aug 1)

OS9.7 Telomere length, TERTp mutation and ALT status in adult diffuse gliomas

Neuro-Oncology : 21 : iii19-iii20 : DOI : 10.1093/neuonc/noz126.065 En savoir plus


The current classification of adult diffuse gliomas integrates two alternative telomere maintenance mechanisms: reactivation of telomerase activity by TERT promoter (TERTp) mutations or ATRX mutations associated with alternative length telomere (ALT). We investigated here the relation between these two mechanisms, telomere length, and outcome in a large series of diffuse gliomas.


We performed C-circle assay (CCA) to determine ALT status, determined telomere length in tumor (RTLt) and leukocyte (RTLl) in a cohort of 354 adult diffuse gliomas, and sequenced ATRX gene. We calculated an age-adjusted telomere score considering tumor and leukocyte (blood) telomere length and corrected by age. This score was used in univariate and multivariate survival analyses to evaluate the potential impact of telomere length on the prognosis of gliomas. We used the TCGA LGG-GBM dataset to validate our findings in an independent cohort.


RTLl and RTLt were associated with ATRX mutation and ALT phenotype, and negatively associated with age and TERTp mutations. ATRX mutations (found in 52% (64/123) of samples) were mostly transitions (C>T or T>C), and were associated with ALT phenotype. None of 1p/19q co-deleted oligodendrogliomas harbored an ALT phenotype. No patients with TERTp mutations had ALT phenotype except for a very small subgroup of patients (3/87, 3.4%) suggesting that multiple ways of telomere maintenance, may co-exist in a single tumor, probably expressed in different clones. Telomere age-adjusted score was independently associated with better outcome (HR= 0.73 [95% CI 0.56–0.97], p-value 0.03 adjusted for age, TERTp mutation, IDH mutation, 1p/19q co-deletion and WHO grade). These results were validated using the LGG-GBM TCGA dataset.


We unravel the relation between RTLl and RTLt, TERTp mutation and ALT phenotype and describe a novel telomere age-adjusted score independently associated with better prognosis in adult diffuse gliomas.

Paulina Prorok, Marie Artufel, Antoine Aze, Philippe Coulombe, Isabelle Peiffer, Laurent Lacroix, Aurore Guédin, Jean-Louis Mergny, Julia Damaschke, Aloys Schepers, Benoit Ballester, Marcel Méchali (2019 Jul 24)

Involvement of G-quadruplex regions in mammalian replication origin activity.

Nature communications : 10 : 3274 : DOI : 10.1038/s41467-019-11104-0 En savoir plus

Genome-wide studies of DNA replication origins revealed that origins preferentially associate with an Origin G-rich Repeated Element (OGRE), potentially forming G-quadruplexes (G4). Here, we functionally address their requirements for DNA replication initiation in a series of independent approaches. Deletion of the OGRE/G4 sequence strongly decreased the corresponding origin activity. Conversely, the insertion of an OGRE/G4 element created a new replication origin. This element also promoted replication of episomal EBV vectors lacking the viral origin, but not if the OGRE/G4 sequence was deleted. A potent G4 ligand, PhenDC3, stabilized G4s but did not alter the global origin activity. However, a set of new, G4-associated origins was created, whereas suppressed origins were largely G4-free. In vitro Xenopus laevis replication systems showed that OGRE/G4 sequences are involved in the activation of DNA replication, but not in the pre-replication complex formation. Altogether, these results converge to the functional importance of OGRE/G4 elements in DNA replication initiation.

Emilia Puig Lombardi, Allyson Holmes, Daniela Verga, Marie-Paule Teulade-Fichou, Alain Nicolas, Arturo Londoño-Vallejo (2019 Jul 9)

Thermodynamically stable and genetically unstable G-quadruplexes are depleted in genomes across species.

Nucleic acids research : 47 : 6098-6113 : DOI : 10.1093/nar/gkz463 En savoir plus

G-quadruplexes play various roles in multiple biological processes, which can be positive when a G4 is involved in the regulation of gene expression or detrimental when the folding of a stable G4 impairs DNA replication promoting genome instability. This duality interrogates the significance of their presence within genomes. To address the potential biased evolution of G4 motifs, we analyzed their occurrence, features and polymorphisms in a large spectrum of species. We found extreme bias of the short-looped G4 motifs, which are the most thermodynamically stable in vitro and thus carry the highest folding potential in vivo. In the human genome, there is an over-representation of single-nucleotide-loop G4 motifs (G4-L1), which are highly conserved among humans and show a striking excess of the thermodynamically least stable G4-L1A (G3AG3AG3AG3) sequences. Functional assays in yeast showed that G4-L1A caused the lowest levels of both spontaneous and G4-ligand-induced instability. Analyses across 600 species revealed the depletion of the most stable G4-L1C/T quadruplexes in most genomes in favor of G4-L1A in vertebrates or G4-L1G in other eukaryotes. We discuss how these trends might be the result of species-specific mutagenic processes associated to a negative selection against the most stable motifs, thus neutralizing their detrimental effects on genome stability while preserving positive G4-associated biological roles.