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Physiological and pathological roles of FATP-mediated lipid droplets in Drosophila and mice retina.

Author(s) : Van Den Brink D, Cubizolle A, Chatelain G, Davoust N, Girard V, Johansen S, Napoletano F, Dourlen P, Guillou L, Angebault-Prouteau C, Bernoud-Hubac N, Guichardant M, Brabet P, Mollereau B,
Journal : PLoS Genet
Increasing evidence suggests that dysregulation of lipid metabolism is associated with neurodegeneration in retinal diseases such as age-related macular degeneration and in brain disorders such as Alzheimer's and Parkinson's diseases. Lipid storage organelles (lipid droplets, LDs), accumulate in many cell types inresponse to stress, and it is now clear that LDs function not only as lipid stores but also as dynamic regulators of the stress response. However, whether these LDs are always protective or can also be deleterious to the cell is unknown. Here, we investigated the consequences of LD accumulation on retinal cell homeostasis under physiological and stress conditions in Drosophila and in mice. In wild-type Drosophila, we show that dFatp is required and sufficient forexpansion of LD size in retinal pigment cells (RPCs) and that LDs in RPCs are required for photoreceptor survival during aging. Similarly, in mice, LD accumulation induced by RPC-specific expression of human FATP1 was non-toxic andpromoted mitochondrial energy metabolism in RPCs and non-autonomously in photoreceptor cells. In contrast, the inhibition of LD accumulation by dFatp knockdown suppressed neurodegeneration in Aats-metFB Drosophila mutants, which carry elevated levels of reactive oxygen species (ROS). This suggests that abnormal turnover of LD may be toxic for photoreceptors cells of the retina under oxidative stress. Collectively, these findings indicate that FATP-mediated LD formation in RPCs promotes RPC and neuronal homeostasis under physiological conditions but could be deleterious for the photoreceptors under pathological conditions.

Promoting the clearance of neurotoxic proteins in neurodegenerative disorders of ageing.

Author(s) : Boland B, Yu W, Corti O, Mollereau B, Henriques A, Bezard E, Pastores G, Rubinsztein D, Nixon R, Duchen M, Mallucci G, Kroemer G, Levine B, Eskelinen E, Mochel F, Spedding M, Louis C, Martin O, Millan M,
Journal : Nat Rev Drug Discov
Neurodegenerative disorders of ageing (NDAs) such as Alzheimer disease, Parkinson disease, frontotemporal dementia, Huntington disease and amyotrophic lateral sclerosis represent a major socio-economic challenge in view of their high prevalence yet poor treatment. They are often called 'proteinopathies' owing to the presence of misfolded and aggregated proteins that lose their physiological roles and acquire neurotoxic properties. One reason underlying the accumulation and spread of oligomeric forms of neurotoxic proteins is insufficient clearance by the autophagic-lysosomal network. Several other clearance pathways are also compromised in NDAs: chaperone-mediated autophagy, the ubiquitin-proteasome system, extracellular clearance by proteases and extrusion into the circulation via the blood-brain barrier and glymphatic system. This article focuses on emerging mechanisms for promoting the clearance of neurotoxic proteins, a strategy that may curtail the onset and slow the progression of NDAs.

SINCERITIES: inferring gene regulatory networks from time-stamped single cell transcriptional expression profiles

Author(s) : Papili Gao N, Ud-Dean S, Gandrillon O, Gunawan R,
Journal : Bioinformatics

Strengths and Weaknesses of the Current Strategies to Map and Characterize R-Loops.

Author(s) : Vanoosthuyse V,
Journal : Noncoding RNA
R-loops are evolutionarily conserved three-stranded structures that result from the formation of stable DNA:RNA hybrids in the genome. R-loops have attracted increasing interest in recent years as potent regulators of gene expression and genome stability. In particular, their strong association with severe replication stress makes them potential oncogenic structures. Despite their importance, the rules that govern their formation and their dynamics are still controversial andan in-depth description of their direct impact on chromatin organization and DNAtransactions is still lacking. To better understand the diversity of R-loop functions, reliable, accurate, and quantitative mapping techniques, as well as functional assays are required. Here, I review the different approaches that arecurrently used to do so and to highlight their individual strengths and weaknesses. In particular, I review the advantages and disadvantages of using the S9.6 antibody to map R-loops in vivo in an attempt to propose guidelines for best practices.

Structural model of the full-length Ser/Thr protein kinase StkP from S. pneumoniae and its recognition of peptidoglycan fragments.

Author(s) : Righino B, Galisson F, Pirolli D, Vitale S, Rety S, Gouet P, De Rosa M,
Journal : J Biomol Struct Dyn
The unique eukaryotic-like Ser/Thr protein kinases of Streptococcus pneumoniae, StkP, plays a primary role in the cell division process. It is composed of an intracellular kinase domain, a transmembrane helix and four extracellular PASTA subunits. PASTA domains were shown to interact with cell wall fragments but the key questions related to the molecular mechanism governing ligand recognition remain unclear. To address this issue, the full-length structural model of StkP was generated by combining small-angle X-ray scattering data with the results ofcomputer simulations. Docking and molecular dynamics studies on the generated three-dimensional model structure reveal the possibility of peptidoglycan fragment binding at the hinge regions between PASTA subunits with a preference for a bent hinge between PASTA3 and PASTA4.

TADs are 3D structural units of higher-order chromosome organization in Drosophila.

Author(s) : Szabo Q, Jost D, Chang J, Cattoni D, Papadopoulos G, Bonev B, Sexton T, Gurgo J, Jacquier C, Nollmann M, Bantignies F, Cavalli G,
Journal : Sci Adv
Deciphering the rules of genome folding in the cell nucleus is essential to understand its functions. Recent chromosome conformation capture (Hi-C) studies have revealed that the genome is partitioned into topologically associating domains (TADs), which demarcate functional epigenetic domains defined by combinations of specific chromatin marks. However, whether TADs are true physical units in each cell nucleus or whether they reflect statistical frequencies of measured interactions within cell populations is unclear. Using a combination ofHi-C, three-dimensional (3D) fluorescent in situ hybridization, super-resolutionmicroscopy, and polymer modeling, we provide an integrative view of chromatin folding in Drosophila. We observed that repressed TADs form a succession of discrete nanocompartments, interspersed by less condensed active regions. Single-cell analysis revealed a consistent TAD-based physical compartmentalization of the chromatin fiber, with some degree of heterogeneity in intra-TAD conformations and in cis and trans inter-TAD contact events. These results indicate that TADs are fundamental 3D genome units that engage in dynamic higher-order inter-TAD connections. This domain-based architecture is likely to play a major role in regulatory transactions during DNA-dependent processes.

The Ectodysplasin receptor EDAR acts as a tumor suppressor in melanoma by conditionally inducing cell death.

Author(s) : Vial J, Royet A, Cassier P, Tortereau A, Dinvaut S, Maillet D, Gratadou-Hupon L, Creveaux M, Sadier A, Tondeur G, Leon S, Depaepe L, Pantalacci S, de la Fouchardiere A, Micheau O, Dalle S, Laudet V, Mehlen P, Castets M,
Journal : Cell Death Differ
Ectodysplasin receptor EDAR is seen as a typical Tumor Necrosis Factor receptor (TNFR) family member known to interact with its ligand Eda-A1, and signaling mainly through the nuclear factor-kappaB (NF-kappaB) and c-jun N-terminal kinases pathways. Mutations in genes that encode proteins involved in EDAR transduction cascade cause anhidrotic ectodermal dysplasia. Here, we report an unexpected pro-apoptotic activity of EDAR when unbound to its ligand Eda-A1, which is independent of NF-kappaB pathway. Contrarily to other death receptors, EDAR doesrecruit caspase-8 to trigger apoptosis but solely upon ligand withdrawal, thereby behaving as the so-called dependence receptors. We propose that pro-apoptotic activity of unbound EDAR confers it a tumor suppressive activity. Along this line, we identified loss-of-pro-apoptotic function mutations in EDAR gene in human melanoma. Moreover, we show that the invalidation of EDAR in mice promotesmelanoma progression in a B-Raf mutant background. Together, these data support the view that EDAR constrains melanoma progression by acting as a dependence receptor.

The hpRNA/RNAi Pathway Is Essential to Resolve Intragenomic Conflict in the Drosophila Male Germline.

Author(s) : Lin C, Hu F, Dubruille R, Vedanayagam J, Wen J, Smibert P, Loppin B, Lai E,
Journal : Dev Cell
Intragenomic conflicts are fueled by rapidly evolving selfish genetic elements, which induce selective pressures to innovate opposing repressive mechanisms. This is patently manifest in sex-ratio (SR) meiotic drive systems, in which distorterand suppressor factors bias and restore equal transmission of X and Y sperm. Here, we reveal that multiple SR suppressors in Drosophila simulans (Nmy and Tmy) encode related hairpin RNAs (hpRNAs), which generate endo-siRNAs that repress the paralogous distorters Dox and MDox. All components in this drive network are recently evolved and largely testis restricted. To connect SR hpRNA function to the RNAi pathway, we generated D. simulans null mutants of Dcr-2 and AGO2. Strikingly, these core RNAi knockouts massively derepress Dox and MDox and are in fact completely male sterile and exhibit highly defective spermatogenesis. Altogether, our data reveal how the adaptive capacity of hpRNAs is critically deployed to restrict selfish gonadal genetic systems that can exterminate a species.

The lysosomal membrane protein LAMP2A promotes autophagic flux and prevents SNCA-induced Parkinson disease-like symptoms in the Drosophila brain.

Author(s) : Issa A, Sun J, Petitgas C, Mesquita A, Dulac A, Robin M, Mollereau B, Jenny A, Cherif-Zahar B, Birman S,
Journal : Autophagy
The autophagy-lysosome pathway plays a fundamental role in the clearance of aggregated proteins and protection against cellular stress and neurodegenerativeconditions. Alterations in autophagy processes, including macroautophagy and chaperone-mediated autophagy (CMA), have been described in Parkinson disease (PD). CMA is a selective autophagic process that depends on LAMP2A (lysosomal-associated membrane protein 2A), a mammal and bird-specific membrane glycoprotein that translocates cytosolic proteins containing a KFERQ-like peptide motif across the lysosomal membrane. Drosophila reportedly lack CMA and use endosomal microautophagy (eMI) as an alternative selective autophagic process. Here we report that neuronal expression of human LAMP2A protected Drosophila against starvation and oxidative stress, and delayed locomotor decline in aging flies without extending their lifespan. LAMP2A also prevented the progressive locomotor and oxidative defects induced by neuronal expression of PD-associated human SNCA (synuclein alpha) with alanine-to-proline mutation at position 30 (SNCA(A30P)). Using KFERQ-tagged fluorescent biosensors, we observed that LAMP2Aexpression stimulated selective autophagy in the adult brain and not in the larval fat body, but did not increase this process under starvation conditions. Noteworthy, we found that neurally expressed LAMP2A markedly upregulated levels of Drosophila Atg5, a key macroautophagy initiation protein, and that it increased the density of Atg8a/LC3-positive puncta, which reflects the formationof autophagosomes. Furthermore, LAMP2A efficiently prevented accumulation of theautophagy defect marker Ref(2)P/p62 in the adult brain under acute oxidative stress. These results indicate that LAMP2A can potentiate autophagic flux in theDrosophila brain, leading to enhanced stress resistance and neuroprotection. ABBREVIATIONS: Act5C: actin 5C; a.E.: after eclosion; Atg5: autophagy-related 5;Atg8a/LC3: autophagy-related 8a; CMA: chaperone-mediated autophagy; DHE: dihydroethidium; elav: embryonic lethal abnormal vision; eMI: endosomal microautophagy; ESCRT: endosomal sorting complexes required for transport; GABARAP: GABA typeA receptor-associated protein; Hsc70-4: heat shock protein cognate 4; HSPA8/Hsc70: heat shock protein family A (Hsp70) member 8; LAMP2: lysosomal associated membrane protein 2; MDA: malondialdehyde; PA-mCherry: photoactivable mCherry; PBS: phosphate-buffered saline; PCR: polymerase chain reaction; PD: Parkinson disease; Ref(2)P/p62: refractory to sigma P; ROS: reactive oxygen species; RpL32/rp49: ribosomal protein L32; RT-PCR: reverse transcription polymerase chain reaction; SING: startle-induced negative geotaxis; SNCA/alpha-synuclein: synuclein alpha; SQSTM1/p62: sequestosome 1; TBS: Tris-buffered saline; UAS: upstream activating sequence.

The RNA helicase DDX17 controls the transcriptional activity of REST and the expression of proneural microRNAs in neuronal differentiation.

Author(s) : Lambert M, Terrone S, Giraud G, Benoit-Pilven C, Cluet D, Combaret V, Mortreux F, Auboeuf D, Bourgeois C,
Journal : Nucleic Acids Res
The Repressor Element 1-silencing transcription factor (REST) represses a numberof neuronal genes in non-neuronal cells or in undifferentiated neural progenitors. Here, we report that the DEAD box RNA helicase DDX17 controls important REST-related processes that are critical during the early phases of neuronal differentiation. First, DDX17 associates with REST, promotes its binding to the promoter of a subset of REST-targeted genes and co-regulates REST transcriptional repression activity. During neuronal differentiation, we observed a downregulation of DDX17 along with that of the REST complex that contributes to the activation of neuronal genes. Second, DDX17 and its paralog DDX5 regulate the expression of several proneural microRNAs that are known to target the REST complex during neurogenesis, including miR-26a/b that are also direct regulatorsof DDX17 expression. In this context, we propose a new mechanism by which RNA helicases can control the biogenesis of intronic miRNAs. We show that the processing of the miR-26a2 precursor is dependent on RNA helicases, owing to an intronic regulatory region that negatively impacts on both miRNA processing and splicing of its host intron. Our work places DDX17 in the heart of a pathway involving REST and miRNAs that allows neuronal gene repression.