Yann Gibert

Bio: Yann Gibert is an academic researcher from University of Mississippi Medical Center. The author has contributed to research in topics: Zebrafish & Biology. The author has an hindex of 22, co-authored 70 publications receiving 1445 citations. Previous affiliations of Yann Gibert include University of Konstanz & Beth Israel Deaconess Medical Center.

Estrogen-related receptor γ is an in vivo receptor of bisphenol A

Abstract: Bisphenol A (BPA) is an endocrine disruptor that displays estrogenic activity. Several reports suggest that BPA may have estrogen receptor-independent effects. In zebrafish, 50 muM BPA exposure induces otic vesicle abnormalities, including otolith aggregation. The purpose of this study was to test if BPA action was mediated in vivo during zebrafish development by the orphan nuclear estrogen related receptor (ERR) gamma. Combining pharmacological and functional approaches, we demonstrate that the zebrafish ERRgamma mediates BPA-induced malformations in otoliths. Using different bisphenol derivatives, we show that different compounds can induce a similar otolith phenotype than BPA and that the binding affinity of these derivatives to the zebrafish ERRgamma correlates with their ability to induce otolith malformations. Morpholino knockdown of ERRgamma function suppresses the BPA effect on otoliths whereas overexpression of ERRgamma led to a BPA-like otolith phenotype. Moreover, a subphenotypical dose of BPA (1 muM) combined with ERRgamma overexpression led to a full-dose (50 muM) BPA otolith phenotype. We therefore conclude that ERRgamma mediates the otic vesicle phenotype generated by BPA. Our results suggest that the range of pathways perturbed by this compound and its potential harmful effect are larger than expected.-Tohme, M., Prud'homme, S. M., Boulahtouf, A., Samarut, E., Brunet, F., Bernard, L., Bourguet, W., Gibert, Y., Balaguer, P., Laudet, V. Estrogen-related receptor gamma is an in vivo receptor of bisphenol A.

Induction and prepatterning of the zebrafish pectoral fin bud requires axial retinoic acid signaling

Abstract: Vertebrate forelimbs arise as bilateral appendages from the lateral plate mesoderm (LPM). Mutants in aldh1a2 (raldh2), an embryonically expressed gene encoding a retinoic acid (RA)-synthesizing enzyme, have been used to show that limb development and patterning of the limb bud are crucially dependent on RA signaling. However, the timing and cellular origin of RA signaling in these processes have remained poorly resolved. We have used genetics and chemical modulators of RA signaling to resolve these issues in the zebrafish. By rescuing pectoral fin induction in the aldh1a2/neckless mutant with exogenous RA and by blocking RA signaling in wild-type embryos, we find that RA acts as a permissive signal that is required during the six- to eight-somite stages for pectoral fin induction. Cell-transplantation experiments show that RA production is not only crucially required from flanking somites, but is sufficient to permit fin bud initiation when the trunk mesoderm is genetically ablated. Under the latter condition, intermediate mesoderm alone cannot induce the pectoral fin field in the LPM. We further show that induction of the fin field is directly followed by a continued requirement for somite-derived RA signaling to establish a prepattern of anteroposterior fates in the condensing fin mesenchyme. This process is mediated by the maintained expression of the transcription factor hand2, through which the fin field is continuously posteriorized, and lasts up to several hours prior to limb-budding. Thus, RA signaling from flanking somites plays a dual early role in the condensing limb bud mesenchyme.

The Phytoestrogen Genistein Affects Zebrafish Development through Two Different Pathways

Abstract: BACKGROUND Endocrine disrupting chemicals are widely distributed in the environment and derive from many different human activities or can also be natural products synthesized by plants or microorganisms. The phytoestrogen, genistein (4', 5, 7-trihydroxy-isoflavone), is a naturally occurring compound found in soy products. Genistein has been the subject of numerous studies because of its known estrogenic activity. METHODOLOGY/PRINCIPAL FINDINGS We report that genistein exposure of zebrafish embryos induces apoptosis, mainly in the hindbrain and the anterior spinal cord. Timing experiments demonstrate that apoptosis is induced during a precise developmental window. Since adding ICI 182,780, an ER antagonist, does not rescue the genistein-induced apoptosis and since there is no synergistic effect between genistein and estradiol, we conclude that this apoptotic effect elicited by genistein is estrogen-receptors independent. However, we show in vitro, that genistein binds and activates the three zebrafish estrogen receptors ERalpha, ERbeta-A and ERbeta-B. Furthermore using transgenic ERE-Luciferase fish we show that genistein is able to activate the estrogen pathway in vivo during larval stages. Finally we show that genistein is able to induce ectopic expression of the aromatase-B gene in an ER-dependent manner in the anterior brain in pattern highly similar to the one resulting from estrogen treatment at low concentration. CONCLUSION/SIGNIFICANCE TAKEN TOGETHER THESE RESULTS INDICATE THAT GENISTEIN ACTS THROUGH AT LEAST TWO DIFFERENT PATHWAYS IN ZEBRAFISH EMBRYOS: (i) it induces apoptosis in an ER-independent manner and (ii) it regulates aromatase-B expression in the brain in an ER-dependent manner. Our results thus highlight the multiplicity of possible actions of phytoestrogens, such as genistein. This suggests that the use of standardized endpoints to study the effect of a given compound, even when this compound has well known targets, may carry the risk of overlooking interesting effects of this compound.

Syndromes of the Head and Neck

Abstract: British authors are the natural heirs to Charles Dickens and Graham Greene.) Nevertheless there are advantages to British readers in a British book especially, for instance, in the chapter on social paediatrics and occasionally as regards therapeutics. The new Forfar and Arneil is, like its predecessors, a good book. There are many new authors and much of it has been completely rewritten. Each chapter has a long list of references, many of them to further reading in books and important 'landmark' papers rather than to very recent original work, and that seems appropriate for a textbook of this nature. It is up to date, including references to topics such as oesophageal pH monitoring in gastrooesophageal reflux, the value of steroids in bacterial meningitis, a full account of the peroxisomal disorders, the significance of dystrophin in muscular dystrophy, the importance of vitamin A in reducing mortality in third world countries, and the use of sumatriptan in migraine and of vigabatrin and lamotrigine in epilepsy. Surprisingly, neither in this nor in Nelson's textbook could I find any reference to Angelman's syndrome. Some topics chosen at random such as Prader-Willi syndrome or haemolytic uraemic syndrome were discussed more fully in the British textbook. There is a surprising omission, however, and that is the chapter on disorders ofear, nose, and throat. Adenoids, glue ear or secretory otitis media, tonsillitis, and tonsillectomy have all been dropped from the index and deafness is dealt with in the chapter on neurology. If you look up 'tonsils' you will be referred to any entry which reads: 'Tonsils: size, presence of infection, exudate, pitting, peritonsillar swelling?'. The index entry 'ear, nose and throat problems' refers to a brief account of such problems in children with cleft palate. It is one of those crazy facts of modern life that the American book costs £60, the British £125. Who will read this new edition? I shall, and I suppose many other consultant paediatricians will also use it as a standard reference book. Undergraduate students will need a more compact text for their basic reading but should use it to look up specific topics, and doctors studying for the MRCP in paediatrics should make a systematic assault on it to provide them with a personal database to be supplemented by journals and monographs. As a textbook of British paediatrics it has no competition and it remains an excellent work of reference which must be available in all paediatric departments in Britain, but the absence of the chapter on ear, nose, and throat disorders must surely be an error and there is clearly a marketing problem for British publishers faced with American competition. If we want British textbooks, and I would not like to think that the time will be forced upon us when we shall have no choice, then it looks as if we must be prepared to pay for the privilege. DOUG ADDY Consultant paediatrician

Genetic compensation induced by deleterious mutations but not gene knockdowns

Abstract: Cells sense their environment and adapt to it by fine-tuning their transcriptome. Wired into this network of gene expression control are mechanisms to compensate for gene dosage. The increasing use of reverse genetics in zebrafish, and other model systems, has revealed profound differences between the phenotypes caused by genetic mutations and those caused by gene knockdowns at many loci, an observation previously reported in mouse and Arabidopsis. To identify the reasons underlying the phenotypic differences between mutants and knockdowns, we generated mutations in zebrafish egfl7, an endothelial extracellular matrix gene of therapeutic interest, as well as in vegfaa. Here we show that egfl7 mutants do not show any obvious phenotypes while animals injected with egfl7 morpholino (morphants) exhibit severe vascular defects. We further observe that egfl7 mutants are less sensitive than their wild-type siblings to Egfl7 knockdown, arguing against residual protein function in the mutants or significant off-target effects of the morpholinos when used at a moderate dose. Comparing egfl7 mutant and morphant proteomes and transcriptomes, we identify a set of proteins and genes that are upregulated in mutants but not in morphants. Among them are extracellular matrix genes that can rescue egfl7 morphants, indicating that they could be compensating for the loss of Egfl7 function in the phenotypically wild-type egfl7 mutants. Moreover, egfl7 CRISPR interference, which obstructs transcript elongation and causes severe vascular defects, does not cause the upregulation of these genes. Similarly, vegfaa mutants but not morphants show an upregulation of vegfab. Taken together, these data reveal the activation of a compensatory network to buffer against deleterious mutations, which was not observed after translational or transcriptional knockdown.