Hypertension 66 (20.3%) 24 (24.2%) 30 (16.3%) NS Diabetes 20 (6.2%) 7 (7.1%) 10 (5.4%) NS Excess weight 78 (24%) 27 (27.3%) 44 (23.9%) NS Smokers 64 (19.7%) 17 (17.2%) 35 (19.0%) NS Age >50 years 137 (42.2%) 54 (54.5%) 67 (36.4%) <0.02 Kidney disease 7 (2.2%) 1 (1%) 5 (2.7%) NS Family history, DM 102 (31.4%) 28 (28.3%) 66 (35.9%) NS

Conflict of interest statement. None declared.

Plant genomes encode various small RNAs that function in distinct, yet overlapping, genetic and epigenetic silencing pathways. However, the abundance and diversity of small-RNA classes varies among plant species, suggesting coevolution between environmental adaptations and gene-silencing mechanisms. Biogenesis of small RNAs in plants is well understood, but we are just beginning to uncover their intricate regulation and activity. Here, we discuss the biogenesis of plant small RNAs, such as microRNAs, secondary siRNAs and heterochromatic siRNAs, and their diverse cellular and developmental functions, including in reproductive transitions, genomic imprinting and paramutation. We also discuss the diversification of small-RNA-directed silencing pathways through the expansion of RNA-dependent RNA polymerases, DICER proteins and ARGONAUTE proteins.

/pdf/the-expanding-world-of-small-rnas-in-plants-1ouxzc3mtq.pdf

The expanding world of small RNAs in plants

Transcriptome-wide Mapping Reveals Widespread Dynamic-Regulated Pseudouridylation of ncRNA and mRNA

Pseudouridine is the most abundant RNA modification, yet except for a few well-studied cases, little is known about the modified positions and their function(s). Here, we develop Ψ-seq for transcriptome-wide quantitative mapping of pseudouridine. We validate Ψ-seq with spike-ins and de novo identification of previously reported positions and discover hundreds of unique sites in human and yeast mRNAs and snoRNAs. Perturbing pseudouridine synthases (PUS) uncovers which pseudouridine synthase modifies each site and their target sequence features. mRNA pseudouridinylation depends on both site-specific and snoRNA-guided pseudouridine synthases. Upon heat shock in yeast, Pus7p-mediated pseudouridylation is induced at >200 sites, and PUS7 deletion decreases the levels of otherwise pseudouridylated mRNA, suggesting a role in enhancing transcript stability. rRNA pseudouridine stoichiometries are conserved but reduced in cells from dyskeratosis congenita patients, where the PUS DKC1 is mutated. Our work identifies an enhanced, transcriptome-wide scope for pseudouridine and methods to dissect its underlying mechanisms and function.

Pseudouridine (ψ) is a C-linked uracil modification originally discovered in tRNA. MS analysis and CeU-Seq, a method that permits chemical tagging, pulldown and sequencing of ψ residues, reveal that these modifications are more abundant in the mammalian transcriptome than previously thought.

Chemical pulldown reveals dynamic pseudouridylation of the mammalian transcriptome.

Thermodynamic data are reported revealing that pseudouridine ()) can stabilize RNA duplexes when replacing U and forming )-A, )-G, )-U and )-C pairs. Stabilization is dependent on type of base pair, position of ) within the RNA duplex, and type and orientation of adjacent Watson–Crick pairs. NMR spectra demonstrate that for internal )-A, )-G and )-U pairs, the N3 imino proton is hydrogen bonded to the opposite strand nucleotide and the N1 imino proton may also be hydrogen bonded. CD spectra show that general A-helix structure is preserved, but there is some shifting of peaks and changing of intensities. ) has two hydrogen donors (N1 and N3 imino protons) and two hydrogen bond acceptors because the glycosidic bond is C-C rather than C-N as in uridine. This greater structural potential may allow ) to behave as a kind of structurally driven universal base because it can enhance stability relative to U when paired with A, G, U or C inside a double helix. These structural and thermodynamic properties may contribute to the biological functions of ).

The contribution of pseudouridine to stabilities and structure of RNAs

Trinucleotide repeats are microsatellite sequences that are polymorphic in length. Their expansion in specific genes underlies a number of neurodegenerative disorders. Using ultraviolet-visible, circular dichroism, nuclear magnetic resonance (NMR) spectroscopies and electrospray ionization mass spectrometry, the structural preferences of RNA molecules composed of two and four repeats of AGG, CGG and UGG in the presence of K + , Na + and NH4 + were analysed. (AGG)2A, (AGG)4A, p(UGG)2U and p(UGG)4U strongly prefer folding into G-quadruplexes, whereas CGG-containing sequences can adopt different types of structure depending on the cation and on the number of repeats. In particular, the two-repeat CGG sequence folds into a G-quadruplex in potassium buffer. We also found that each G-quadruplex fold is different: A:(G:G:G:G)A hexads were found for (AGG)2A, whereas mixed G:C:G:C tetrads and U-tetrads were observed in the NMR spectra of G(CGG)2 Ca nd p(UGG)2U, respectively. Finally, our NMR study highlights the influence of the strand sequence on the structure formed, and the influence of the intracellular environment on the folding. Importantly, we highlight that although potassium ions are prevalent in cells, the structures observed in the HeLa cell extract are not always the same as those prevailing in biophysical studies in the presence of K + ions.

https://www.hal.inserm.fr/inserm-01260985/document

Distinctive structural motifs of RNA G-quadruplexes composed of AGG, CGG and UGG trinucleotide repeats

G-quadruplexes are non-canonical secondary structures which may be formed by guanine rich sequences, both in vitro and in living cells. The number of biological functions assigned to these structural motifs has grown rapidly since the discovery of their involvement in the telomere maintenance. Knowledge of the three-dimensional structures of G-quadruplexes plays an important role in understanding their conformational diversity, physiological functions, and in the design of novel drugs targeting G-quadruplexes. For the last decades, structural studies have been mainly focused on the DNA G-quadruplexes. Their RNA counterparts gained an increased interest along with still-emerging recognition of the central role of RNA in multiple cellular processes. In this review we focus on structural properties of RNA G-quadruplexes, based on high-resolution structures, available in RCSB PDB data base and on structural models. In addition, we point out to the current challenges in this field of research.

/pdf/overview-of-the-rna-g-quadruplex-structures-j9ibdv3la8.pdf

Overview of the RNA G-quadruplex structures.

Pseudouridine (Ψ) is the most common chemical modification present in RNA. In general, Ψ increases the thermodynamic stability of RNA. However, the degree of stabilization depends on the sequence and structural context. To explain experimentally observed sequence dependence of the effect of Ψ on the thermodynamic stability of RNA duplexes, we investigated the structure, dynamics and hydration of RNA duplexes with an internal Ψ-A base pair in different nearest-neighbor sequence contexts. The structures of two RNA duplexes containing 5'-GΨC/3'-CAG and 5'-CΨG/3'-GAC motifs were determined using NMR spectroscopy. To gain insight into the effect of Ψ on duplex dynamics and hydration, we performed molecular dynamics (MD) simulations of RNA duplexes with 5'-GΨC/3'-CAG, 5'-CΨG/3'-GAC, 5'-AΨU/3'-UAA and 5'-UΨA/3'-AAU motifs and their unmodified counterparts. Our results showed a subtle impact from Ψ modification on the structure and dynamics of the RNA duplexes studied. The MD simulations confirmed the change in hydration pattern when U is replaced with Ψ. Quantum chemical calculations showed that the replacement of U with Ψ affected the intrinsic stacking energies at the base pair steps depending on the sequence context. The calculated intrinsic stacking energies help to explain the experimentally observed sequence dependent changes in the duplex stability from Ψ modification.

/pdf/computational-and-nmr-studies-of-rna-duplexes-with-an-4z4j8b7a9l.pdf

Computational and NMR studies of RNA duplexes with an internal pseudouridine-adenosine base pair.

All guanine-rich DNA and RNA molecules tend to fold into inter- and intra-molecular structures called G-quadruplexes. The core of a G-quadruplex is composed of at least two adjacent G-tetrads stabilized by monovalent cations. While it has been suggested that there could potentially be over 375 000 quadruplex forming sequences in the human genome alone, only a small number of three-dimensional G-quadruplex structures are known. More structural data are needed to explain their presence and function in vivo. We offer here a short review of experimental methods commonly used to determine G-quadruplex topologies.

/pdf/how-to-study-g-quadruplex-structures-4gbw8w8zby.pdf

Magdalena Malgowska

Papers

The contribution of pseudouridine to stabilities and structure of RNAs

Distinctive structural motifs of RNA G-quadruplexes composed of AGG, CGG and UGG trinucleotide repeats

Overview of the RNA G-quadruplex structures.

Computational and NMR studies of RNA duplexes with an internal pseudouridine-adenosine base pair.

How to study G-quadruplex structures