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Landes T.,Toulouse 1 University Capitole | Leroy I.,Toulouse 1 University Capitole | Bertholet A.,Toulouse 1 University Capitole | Diot A.,Toulouse 1 University Capitole | And 11 more authors.
Seminars in Cell and Developmental Biology | Year: 2010

Mitochondrial morphology varies according to cell type and cellular context from an interconnected filamentous network to isolated dots. This morphological plasticity depends on mitochondrial dynamics, a balance between antagonistic forces of fission and fusion. DRP1 and FIS1 control mitochondrial outer membrane fission and Mitofusins its fusion. This review focuses on OPA1, one of the few known actors of inner membrane dynamics, whose mutations provoke an optic neuropathy. Since its first identification in 2000 the characterization of the functions of OPA1 has made rapid progress thus providing numerous clues to unravel the pathogenetic mechanisms of ADOA-1. © 2009 Elsevier Ltd.

SUMO protein with the areas marked with ubiquitin in green. Credit: CNIO Three years ago, the research team directed by Óscar Fernández-Capetillo, head of the Genomic Instability Group at the Spanish National Cancer Research Centre (CNIO), obtained, for the first time, a panoramic view of the proteins that intervene in one of the most important and delicate cellular processes: the copying of genetic material during cellular division. They observed that the parts of the genome where the DNA was copied were also very rich in the modification by some very particular proteins, SUMOylations, and poor in others, ubiquitinations, but they were unable to understand why. The continuation of the paper, published today in the Nature Structural & Molecular Biology journal, reveals how the balance between these chemical markers in these regions is, in fact, key for the division of genetic material. During this process, the USP7 protein travels with an entourage of molecules that form part of the replisome—a set of proteins involved in copying the DNA—and eliminates the ubiquitination marks of proteins in the complex, thus explaining the low concentration of ubiquitin in these areas. "USP7 acts as an traffic officer that regulates the marks or traffic signs near the replisome. Eliminating ubiquitin prevents the proteins at the replisome from being expelled, thus favouring their concentration and the DNA copying process," explains Fernández-Capetillo. As the team described in the previous paper, replisomes contain up to 50 different proteins that participate in the delicate process of copying genetic material. Some proteins open DNA's double helix, others twist it to favour copying, others stabilise it, etc. They all move together through the genome to ensure a complete copy. In order to understand the role of USP7 and its cutting action on ubiquitin marks during the DNA copying process, the researchers used advanced protein tools. "We knew that replisome proteins could present both modifications simultaneously [ubiquitinations and SUMOylations], but we did not know how they worked," explains Fernández-Capetillo. "We now know that USP7 eliminates the ubiquitin marks on proteins that are also SUMOylated in replication areas, which explains why there is a low concentration of ubiquitin and high levels of SUMO." This balance between SUMO and ubiquitin establishes a code that regulates the concentration of proteins in the replisome. "If a protein is SUMOylated, it becomes enriched in the replisome, but if it is also ubiquitinated, it is expelled. This is a code of signals or flags that regulates the concentration of factors in the DNA replication area," say the researchers. Apart from being of academic interest, these studies are relevant for chemotherapy. USP7 inhibitors are currently being studied as possible anti-cancer agents in pre-clinical tests. "The model that had been proposed is that the compounds increase p53 levels, resulting in the suicide of tumour cells. Our data indicate that USP7 is essential for genome replication in cells with or without p53." With these data, the authors of the paper warn that these molecules may not be specifically anti-tumour agents. "We believe they inhibit the cell division process regardless of whether the cells are cancerous or healthy and, therefore, their use for treating cancer in the future will have to be reconsidered." Explore further: Researchers 'capture' the replication of the human genome for the first time More information: Emilio Lecona et al. USP7 is a SUMO deubiquitinase essential for DNA replication, Nature Structural & Molecular Biology (2016). DOI: 10.1038/nsmb.3185

Millions of human cells are constantly dividing to repair tissue damage and ensure continuity. This is one of the most complex cellular processes, and in order for it to be successful, cells must produce a copy of their genetic material (DNA). Researchers from the Spanish National Cancer Research Centre (CNIO) have discovered the critical role of the POLD3 protein in this DNA replication process; without POLD3, cells do not divide, and even the embryonic development process may be curtailed.

In contrast to the cells in the rest of the body, sex cells hold half the number of chromosomes (they are haploid) as a result of this special kind of cell division. In meiosis, a precursor cell —primordial germ cell— produces four spermatozoids during spermatogenesis, while only one oocyte is formed during oogenesis (the other three cells die during the process). Mice deficient in RingoA, generated in Nebreda's Signalling and Cell Cycling Laboratory, are apparently healthy but both sexes are completely sterile. After three years of experiments, IRB Barcelona postdoctoral researchers Petra Mikolcevic and Michitaka Isoda describe the molecular imbalances that occur during meiosis as a result of the absence of this protein. This study sheds new light on a key process for all forms of life that engage in sexual reproduction. "We all start life through meiosis so understanding how this process works is intellectually interesting," says Nebreda. Although meiosis was first described in the late 19th century, "many questions remain unanswered," explains this scientist, holder of a European Research Council grant. "There are no good in vitro models available to study meiosis. It is difficult to extract spermatocytes and to perform studies in plates; they have to be studied in the testicles. And oocytes are even worse because ovules are formed in early stages of development and working with embryos is technically complex." The scientists have discovered that RingoA is a key activator of Cdk2, the protein kinase with which it forms a complex required for meiosis. In fact, the genetic mouse model deficient in Cdk2, which was reported 12 years ago by Mariano Barbacid's group at CNIO, is also viable but sterile and shows the exact same alterations in meiosis as those observed by the researchers at IRB Barcelona. "In biology, if two practically indistinguishable phenotypes are obtained, it is an indication that the proteins have the same function and that they may work together." What was not known until now was that RingoA is the key partner for Cdk2 in meiosis, as Cdk2 normally forms complexes with another family of proteins called cyclins. The study demonstrates that RingoA is active at telomeres—structures that protect the ends of chromosomes and where Cdk2 is also found.  During meiosis, telomeres allow chromosomes to attach to the nuclear membrane, thus allowing them to exchange DNA fragments. This recombination of chromosomes is an essential feature of meiosis. Without the RingoA-Cdk2 complex, the telomeres of the chromosomes do not tether to the membrane but rather float in the nucleus, leading to chaotic recombination. The breaks in DNA needed for fragment exchange are not repaired and thus meiosis is not completed. Consequently, sex cells are not formed. "It would not be unreasonable to consider the development of a male contraceptive based on RingoA-Cdk2 inhibitors," proposes Nebreda. In the same way that women produce oocytes during embryo development, men can produce spermatozoids throughout adulthood. "If the pharmaceutical industry wanted to invest in this field, we have the biochemical techniques set up for the identification of inhibitors." Explore further: Researchers identify first sex chromosome gene involved in meiosis and male infertility More information: Essential role of the Cdk2 activator RingoA in meiotic telomere tethering to the nuclear envelope. Nature Comms. (2016, 30 March): DOI: 10.1038/NCOMMS11084

News Article | August 18, 2016
Site: www.biosciencetechnology.com

Despite their especially compact structure that is difficult to access, telomeres transcribe information like the rest of the DNA. The RNAs resulting from this process are called TERRA and their function is essential in preserving these protective structures. This is the conclusion of a new study by the Telomere and Telomerase Group at the Spanish National Cancer Research Centre (CNIO), which has also located the part of the human genome where these molecules are "manufactured". This finding is consistent with the observations made two years ago by the same group, lead by Maria A. Blasco. On that occasion, they were working on mouse cells and they observed that the TERRA that protect the 20 chromosomes of this mammal originated exclusively in pair 18 and, to a lesser extent, in number 9. In the case of humans, the results now published in Nature Communications indicate that these RNAs are transcribed exclusively at one point. The researchers analysed 18 RNAs previously proposed as possible TERRA but only those arising from the long arm of chromosome 20 (20q) and at the short arm of chromosome X (Xp) showed TERRA features. To demonstrate that the RNAs transcribed at these two points were, indeed, TERRA, the authors genetically removed both loci using the CRISPR-CAS9 technology. They then noted that while the suppression of Xp had no significant consequences, the suppression of 20q had extremely negative effects on telomeres. "Identification of 20q as one of the major locus for human TERRA generation allows us to address the role of TERRA telomere biology," write the authors. After removing it in various cellular lines, they saw that there was a significant increase in DNA and telomere damage, as well as an increase in chromosome instability. This is the first time that the crucial role of TERRA in the preservation of telomeres has been demonstrated in any organism. "These results are striking because they clearly demonstrate that TERRA play an essential role in cell viability as well as in preserving telomeres; they are just as important to the functioning of telomeres as telomerase or shelterins, the proteins that protect the telomeres," explains Blasco. The discovery of the 20q region as the source of TERRA and the confirmation of the key role played by these RNAs in preserving telomeres opens the door to the study of certain syndromes in which alterations in this chromosomal region have been detected. Also, it offers a new path in the study of patients with telomeric disorders in which, however, no alterations in the genes normally involved -telomerase, shelterins- have been found.

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