Gilbert Brun - Academia.edu (original) (raw)

Papers by Gilbert Brun

Cell growth & differentiation : the molecular biology journal of the American Association for Cancer Research, 1998

Retinoblastoma (Rb) protein has been implicated in the control of cell proliferation and malignan... more Retinoblastoma (Rb) protein has been implicated in the control of cell proliferation and malignant transformation in different cell types. To analyze its role as a promoter of cell growth arrest during development, we have studied the temporal pattern of Rb expression and its association with E2F-1 during embryogenesis of the quail neuroretina. During development of this neural organ, most cells stop dividing and begin to differentiate at embryonic days E6 and E7, as indicated by the decline of cyclin-dependent kinase cdk2 and by an increased level of cdk5. At this stage, we observed a shift of hyperphosphorylated Rb protein to its hypophosphorylated form as well as a decrease of the total level of Rb. The Rb-related protein, p107, is also progressively down-regulated from the E7 stage onwards. P130 levels, on the other hand, actually increase. Moreover, cell cycle exit at E6-E7 is characterized by a sudden and transient rise of the E2F-1/RB complex followed by the appearance of the...

The EMBO Journal, 1995

The oncoprotein p60v-src encoded by the Rous sarcoma virus (RSV) genome is the prototype of non-r... more The oncoprotein p60v-src encoded by the Rous sarcoma virus (RSV) genome is the prototype of non-receptor tyrosine kinases. More than 50 targets of p60v src have been described to date. However, the precise mechanisms of RSV tranformation remain to be elucidated. Here, we present the study of a new v-srcactivated gene, NR-13, which encodes a protein identified as a new member of the Bcl-2 family. This protein is localized in the membrane with a pattern already observed with Bcl-2. In quail embryos, this gene is mainly expressed in neural and muscular tissues. Its expression is dramatically down-regulated after embryonic day 7 (E7) in the optic tectum. To evaluate a possible role for NR-13 in the control of apoptotic processes in this particular brain area, in situ hybridization and DNA ladder fractionation studies were performed to correlate NR-13 expression with typical situations of apoptosis during brain development. Our results support the idea that RSV could activate antiapoptotic functions of the host cell resulting in an increase of their lifespan, which could be particularly relevant to tumour formation.

Cell growth & differentiation : the molecular biology journal of the American Association for Cancer Research, 1996

It is a characteristic of the central nervous system of higher eukaryotes that neurons, after an ... more It is a characteristic of the central nervous system of higher eukaryotes that neurons, after an initial proliferation phase, remain postmitotic for their whole life span. In the developing quail neuroretina, most retinoblasts become postmitotic after 7-8 days of incubation. They also cease to express cdc2, which is presumably necessary to allow retinoblasts to definitively leave the cell cycle. The molecular mechanisms monitoring cdc2 expression during differentiation remain partly understood. To further study the control of cdc2 transcription in avian cells, we have cloned the quail cdc2 promoter. Two functional regulatory elements have been characterized. One of them contains an E2F-binding site. Human E2F-1 was found to transactivate the quail cdc2 promoter very efficiently in avian and human cells. Gel retardation experiments are presented, suggesting that E2F, in association with different partners, is a major regulatory of cdc2 transcription during the development of the neur...

Oncogene, Jan 3, 1996

Tumorigenesis can be induced either by activating cell proliferation or by inhibiting metabolic p... more Tumorigenesis can be induced either by activating cell proliferation or by inhibiting metabolic pathways regulating programmed cell death (apoptosis). There is evidence suggesting that p60(v-src) and other tyrosine kinases protect cells against apoptosis. This effect could contribute to cell transformation by the Rous sarcoma virus. Mechanism of cell death inhibition by p60(v-src) remains largely unknown. We have recently reported that in avian cells p60(v-src) activates the expression of nr-13, a bcl-2-related gene. In this paper, we demonstrate, using the bone marrow derived cell line Baf-3 as an experimental model, that the product of this avian gene (nr-13) is a potent anti-apoptotic factor. In addition, we report that, in quail neuroretinal cells, nr-13 expression is activated upon infection by the Rous sarcoma virus (RSV) but not by other oncogenic retroviruses like FSV or MH2, suggesting that nr-13 is a specific target of v-src. Activation of nr-13 expression may be a key ste...

Biology of the Cell, 1992

The International journal of developmental biology, 1997

After an initial proliferation phase, neurons of the central nervous system (CNS) of higher eukar... more After an initial proliferation phase, neurons of the central nervous system (CNS) of higher eukaryotes remain postmitotic during their entire lifespan. This requires that a very stringent control be exerted on the cell division apparatus, whose molecular mechanisms remain quite elusive. Here we have used quail neuroretina as a model to study the control of cell division in the developing CNS. In vertebrates, embryonic neuroretinal cells (NR cells) stop their proliferation at different times depending on the cell type. Most NR cells in the quail embryo become postmitotic between E7 and E8. To acquire a better understanding of the molecular events leading to quiescence in NR cells, we have analyzed the expression of cdc2 and of two activators of p34(cdc2): cyclin A and cyclin B2 in the developing neuroretina. We report that these three proteins are downregulated between E7 and E9, suggesting that a common mechanism could block their transcription in differentiating neurons. We also re...

Http Www Theses Fr, 2002

Le genome humain est constitue de 35000 genes soit seulement 2 a 3 fois plus que celui d'orga... more Le genome humain est constitue de 35000 genes soit seulement 2 a 3 fois plus que celui d'organismes modeles tels que le nematode et la mouche. Ce nombre de gene n'est pas compatible avec la perception de la complexite moleculaire que l'on se faisait de ces differents organismes. Il est apparu que cette complexite moleculaire n'etait pas generee uniquement par le nombre de gene mais aussi par des mecanismes de regulation de l'expression des genes tels que l'usage de differents promoteurs et le processus d'epissage alternatif. Dans le laboratoire, nous avons etudie la regulation de l'expression du gene Otx2. Ce gene code pour un facteur de transcription a homeodomaine dont le role est crucial pour la formation du cerveau. En effet, les souris deficientes pour ce gene ne developpent pas de structures anterieures du cerveau et meurent in utero. L'analyse moleculaire du gene Otx2 a permis de montrer que sa structure est plus complexe que celle qui etait decrite dans la litterature. En effet, nos resultats ont revele l'existence de trois sites d'initiation de la transcription et l'epissage alternatif d'un petit exon de 24 nucleotides dans la sequence codante. Le gene Otx2 est donc transcrit en 6 ARNm responsables de la synthese de deux types de proteine Otx2 distinctes de 8 acides amines dans la region N-terminale. L'etude des patrons d'expression de ces ARNm montre que les domaines d'expression sont identiques a ceux decrits dans la litterature. Cependant, cette analyse montre qu'au cours du developpement embryonnaire, tous les ARNm du gene Otx2 sont exprimes dans les memes regions du cerveau alors qu'au stade adulte, seul un des trois sites d'initiation de la transcription semble etre utilise pour exprimer le gene Otx2. L'ensemble de nos resultats ainsi que ceux de la litterature nous permettent d'entrevoir les differents mecanismes potentiels de la regulation de l'expression du gene Otx2 et de proposer des hypotheses concernant les fonctions des proteines Otx2 dans le cerveau des mammiferes.

Proceedings of the National Academy of Sciences, 1971

Polyribonucleotides will act as efficient templates for the DNA polymerases found in the virions ... more Polyribonucleotides will act as efficient templates for the DNA polymerases found in the virions of avian myeloblastosis virus and mouse leukemia virus if a short complementary oligodeoxyribonucleotide primer is added. Synthesis of the complementary polydeoxyribonucleotide continues until an amount of polymer equal to the amount of initial template has been produced. The two viruses show slightly different specificities toward the four homoribopolymers. Polydeoxyribonucleotides are generally much poorer templates than the homologous polyribonucleotides, in most cases yielding no detectable synthesis. The DNA polymerase of RNA tumor viruses, therefore, have the same requirements for activity as do other DNA polymerases, except that they prefer polyribonucleotides over polydeoxyribonucleotides as templates.

Journal of Neurochemistry, 2003

The mouse Otx2 gene is essential throughout head and brain development, from anterior-posterior p... more The mouse Otx2 gene is essential throughout head and brain development, from anterior-posterior polarity determination and neuroectoderm induction to post-natal sensory organ maturation. These numerous activities must rely on a very finely tuned regulation of expression. In order to understand the molecular control of the Otx2 gene, we set out to isolate its promoter. During this quest, we identified three remote transcription start sites, two defining two new upstream exons and one mapping within the previously reported first exon. The three transcripts differed in their 5¢ non-coding region but encoded the same protein. The transcription start nucleotides of each mRNA species have been mapped by RNase protection assays and by an RNA circularization technique. We have demonstrated that they are all used and linked to functional promoters. In addition to leader versatility, we also detected alternative splicing within the coding sequence that gives rise to a new protein endowed with an 8 amino-acid insertion upstream of the homeodomain. Combined analysis of the relative abundance of Otx2 mRNA isoforms in representative tissues and in situ hybridization studies revealed distinct spatial and temporal, although partially overlapping, expression patterns of the mRNA isoforms. These findings provide new clues to a better understanding of the relationships between Otx2 gene architecture and its complex regulatory requirements.

Journal of Biological Chemistry, 1999

Proliferation and differentiation of progenitor stem cells are mainly controlled by diffusible an... more Proliferation and differentiation of progenitor stem cells are mainly controlled by diffusible and adhesion molecules. Stem cell factor (SCF), an essential regulator of spermatogenesis produced by Sertoli cells, utilize both modes of cell to cell communication. Indeed, SCF exists in soluble (SCFs) and membrane-bound (SCFm) forms, which are required for a complete spermatogenesis, and are generated by alternative splicing of optional exon 6, encoding sites of proteolysis. We show that in the mouse testis, the alternative splicing of SCF is developmentally regulated. SCFs predominates in fetal and neonatal gonads and is then replaced by SCFm in the prepubertal and adult gonads. By sequencing SCF exon 6, we show that the flanking intronic sequences perfectly follow the gt-at rule, suggesting that the basal splicing machinery might not be responsible by itself for exon 6 skipping. Moreover, freshly isolated Sertoli cells mainly express SCFm, but a switch to SCFs occurs after 48 h of culture. We found that this change can be prevented by acidification of the culture medium at pH 6.3 or by addition of lactate. The sustained synthesis of SCFm at low pH was no longer observed in the presence of cycloheximide, suggesting that SCF exon 6 skipping requires de novo protein synthesis. Accordingly, UV cross-linking experiments show that nuclear Sertoli cell protein(s) bind in a sequence-specific manner to exon 6. Together, our data allow the proposal of an integrated mechanism in which the synthesis of lactate by Sertoli cells is used in the same time as an energetic substrate for germ cells and as a promoter of their survival/proliferation through the production of SCFm.

European Journal of Biochemistry, 1974

... The high efficiency of hybrid structures rAn - dTn, dAn * run and rIn * dCn in which RNA acts... more ... The high efficiency of hybrid structures rAn - dTn, dAn * run and rIn * dCn in which RNA acts as initiator and DNA as template suggests an essential role of this enzyme in DNA replication. The enzyme does not catalyze RNA-directed DNA synthesis. ...

Nucleic Acids Research, 1997

Contrary to the membrane-anchored leukemia inhibitory factor receptor (LIFR), the mouse soluble L... more Contrary to the membrane-anchored leukemia inhibitory factor receptor (LIFR), the mouse soluble LIFR is an inhibitor of LIF action, possibly through a ligand titration effect. Two mRNA species encoding the soluble LIFR have been identified. Since the 3′-untranslated end of the shorter form was shown to contain a B2 element, we have examined the possibility that this SINE may be responsible for LIFR mRNA truncation. Transient expression assays, using B2-derived or intron-derived sequences independently or in conjunction, show that the B2 element has fortuitously unmasked a cryptic pre-mRNA 3′ processing activity of silent intron sequences. The corresponding locus of the rat genome has been isolated and was shown to be devoid of any retroposon, which may explain why no soluble LIFR has yet been identified in any other species and further indicates that the B2 insertion event in the mouse LIFR gene has occurred recently during evolution. And yet, a tight tissue-specific regulation of alternative synthesis of soluble and membrane-bound LIFR mRNA has already emerged in mice. These results provide striking evidence for the rapid influence of retroposition on genome expression.

EMBO reports, 2006

To identify the independent spatial and temporal activities of the essential developmental gene O... more To identify the independent spatial and temporal activities of the essential developmental gene Otx2, the germline mutation of which is lethal at embryonic day 8.5, we floxed one allele and substituted the other with an inducible CreER recombinase gene. This makes 'trans' self-knockout possible at any developmental stage. The transient action of tamoxifen pulses allows time-course mutation. We demonstrate efficient temporal knockout and demarcate spatio-temporal windows in which Otx2 controls the head, brain structures and body development.

Reproduction Nutrition Développement

Chez le poulet le virus de l'érythroblastose aviaire (AEV) transforme 'in vitro&dquo; des cellule... more Chez le poulet le virus de l'érythroblastose aviaire (AEV) transforme 'in vitro&dquo; des cellules du tissu conjonctif (CEF), et des précurseurs des cellules érythrocytiques. Il induit chez l'animal des fibrosarcomes et des érythroleucémies. Deux oncogénes viraux, v-erbB et v-erbA, sont responsables de l'activité néoplasique du virus. Le premier oncogéne a été transduit à partir du gène de poulet codant pour le récepteur de l' EGF et au TGFa. Le second correspond à un récepteur tronqué de l'hormone L-Trüodolhyronine (LT3R). Lors de la transduction du géne cellulaire c-erbA, codant pour le LT3R, par le virus, il y a eu délétion de la partie 3' de celui-ci, rendant le produit de v-erbA incapable de fixer l'hormone LT3. Afin d'étudier le rôle spécifique de v-erbA lors de la transformation des précureurs érythrocytiques par AEV, nous avons construit un vecteur rétrovirale, XJ12, associant v-erba au gène de sélection Neo R. L' inlection'in vitro&dquo; de moelle osseuse de

Eur J Biochem, 1977

The level of DNA polymerase gamma as compared to DNA polymerases alpha and beta has been determin... more The level of DNA polymerase gamma as compared to DNA polymerases alpha and beta has been determined in chick embryo by means of specific tests: the amount of gamma-polymerase in the 12-day-old chick embryo reaches about 15% of the total polymerase activity. This enzyme is mainly localized in nuclei and mitochondria, where it represents the prevailing if not the unique DNA polymerase activity. The mitochondrial DNA polymerase gamma is likely to be associated with the internal membrane or the matrix of this organelle since it is not removed by digitonin treatment. The gamma-polymerases have been purified from chick embryo nuclei and mitochondria 500-700 times by means of DEAE-cellulose, phosphocellulose and hydroxyapatite chromatographies. The purified mitochondrial DNA polymerase gamma is closely related to the homologous enzyme purified from the nuclei of the same cells. So far, they cannot be distinguished on the basis of their sedimentation, catalytical properties and response to inhibitors or denaturating agents. The purified gamma enzymes are distinct from the chick embryo DNA polymerases alpha and beta and are not inhibited by antibodies prepared against the latter enzymes. The nuclear and mitochondrial gamma-polymerases do not respond to the oncogenic RNA virus DNA polymerase assay with natural mRNAs.

The level of DNA polymerase y as compared to DNA polymerases a and fl has been determined in chic... more The level of DNA polymerase y as compared to DNA polymerases a and fl has been determined in chick embryo by means of specific tests: the amount of y-polymerase in the 12-day-old chick embryo reaches about 15 %, of the total polymerase activity. This enzyme is mainly localized in nuclei and mitochondria, where it represents the prevailing if not the unique DNA polymerase activity. The mitochondrial DNA polymerase y is likely to be associated with the internal membrane or the matrix of this organelle since it is not removed by digitonin treatment. The y-polymerases have been purified from chick embryo nuclei and mitochondria 500-700 times by means of DEAE-cellulose, phosphocellulose and hydroxyapatite chromatographies. The purified mitochondrial DNA polymerase y is closely related to the homologous enzyme purified from the nuclei of the same cells. So far, they cannot be distinguished on the basis of their sedimentation, catalytical properties and response to inhibitors or denaturating agents. The purified y enzymes are distinct from the chick embryo DNA polymerases a and p and are not inhibited by antibodies prepared against the latter enzymes. The nuclear and mitochondrial y-polymerases do not respond to the oncogenic RNA virus DNA polymerase assay with natural mRNAs.

Journal of cell science, 1997

The molecular events orchestrating neuronal degeneration and regeneration remain poorly understoo... more The molecular events orchestrating neuronal degeneration and regeneration remain poorly understood. Attempts at identifying genes specifically expressed during these processes, have constantly led to the (re)isolation of the clusterin/ApoJ gene, whose expression is highly reactive to injury in a wide variety of tissues. To get insight into the function of clusterin in neuron loss, we have assessed in detail the clusterin gene expression in an experimental model of neurodegeneration, using the peripheral olfactory system of adult mouse. The sensory neurons of olfactory nasal mucosa can be massively induced to degenerate in vivo, by surgical removal of their only synaptic target: the olfactory bulb. We have previously shown that this neuron loss results from a near-synchronized induction of apoptosis genetic programs. We present here evidence that clusterin gene expression is tightly correlated to the onset of neuronal apoptoses in lesioned olfactory mucosae. The simultaneous preparat...

Comptes rendus de l'Académie des sciences. Série III, Sciences de la vie, 1993

Transforming growth factor beta 1 (TGF-beta 1) inhibits growth of primary cultures of chick embry... more Transforming growth factor beta 1 (TGF-beta 1) inhibits growth of primary cultures of chick embryo fibroblasts by affecting G1 and strongly increasing the generation time. This inhibition is reversed by the nuclear oncogenes v-jun, v-fos, v-myc, but not v-erbA and v-ets. It is also reversed by v-myb from either avian myeloblastosis virus or avian E26 retrovirus. Taken together, these results strongly suggest that independent, functional interferences may take place between the TGF-beta 1-induced growth inhibitory pathway and the oncogen-driven stimulatory pathway(s) at the level of the AP-1, Myc, and Myb transcription factors.

Cellular & molecular biology research, 1993

The PUR element has originally been defined in human, as a purine-rich motif present in a DNA rep... more The PUR element has originally been defined in human, as a purine-rich motif present in a DNA replication initiation zone, whose purine strand is capable of binding a single strand-specific factor termed Pur, present in HeLa cell nuclear extracts. We have identified a related DNA element, in the 5' region of the quail clusterin gene, for its positive influence on the transcription of this gene. In the present work, we show that this element does correspond to a novel cis-element of transcription, still active when placed in an heterologous promoter. We also present a series of evidences showing that the avian PUR-specific binding factors are closely related to those previously identified in human. The human Pur alpha protein is capable of binding the quail clusterin PUR element as well as the human c-myc gene-derived PUR element. UV-crosslinking and Southwestern analyses reveal that the Pur factors present in HeLa and avian cells are closely related. The physical interactions wi...

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