Neuronal Circuit Development

Team Publications

Year of publication 2016

Laura Fontenas, Flavia De Santis, Vincenzo Di Donato, Cindy Degerny, Béatrice Chambraud, Filippo Del Bene, Marcel Tawk (2016 Dec 1)

Neuronal Ndrg4 Is Essential for Nodes of Ranvier Organization in Zebrafish.

PLoS genetics : e1006459 : DOI : 10.1371/journal.pgen.1006459 Learn more
Summary

Axon ensheathment by specialized glial cells is an important process for fast propagation of action potentials. The rapid electrical conduction along myelinated axons is mainly due to its saltatory nature characterized by the accumulation of ion channels at the nodes of Ranvier. However, how these ion channels are transported and anchored along axons is not fully understood. We have identified N-myc downstream-regulated gene 4, ndrg4, as a novel factor that regulates sodium channel clustering in zebrafish. Analysis of chimeric larvae indicates that ndrg4 functions autonomously within neurons for sodium channel clustering at the nodes. Molecular analysis of ndrg4 mutants shows that expression of snap25 and nsf are sharply decreased, revealing a role of ndrg4 in controlling vesicle exocytosis. This uncovers a previously unknown function of ndrg4 in regulating vesicle docking and nodes of Ranvier organization, at least through its ability to finely tune the expression of the t-SNARE/NSF machinery.

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F De Santis, V Di Donato, F Del Bene (2016 Jul 23)

Clonal analysis of gene loss of function and tissue-specific gene deletion in zebrafish via CRISPR/Cas9 technology.

Methods in cell biology : 171-88 : DOI : 10.1016/bs.mcb.2016.03.006 Learn more
Summary

In the last few years the development of CRISPR/Cas 9-mediated genome editing techniques has allowed the efficient generation of loss-of-function alleles in several model organisms including zebrafish. However, these methods are mainly devoted to target-specific genomic loci leading to the creation of constitutive knock-out models. On the contrary, the analysis of gene function via tissue- or cell-specific mutagenesis remains challenging in zebrafish. To circumvent this limitation, we present here a simple and versatile protocol to achieve tissue-specific gene disruption based on the Cas9 expression under the control of the Gal4/upstream activating sequence binary system. In our method, we couple Cas9 with green fluorescent protein or Cre reporter gene expression. This strategy allows us to induce somatic mutations in genetically labeled cell clones or single cells, and to follow them in vivo via reporter gene expression. Importantly, because none of the tools that we present here are restricted to zebrafish, similar approaches are readily applicable in virtually any organism where transgenesis and DNA injection are feasible.

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Carole Gauron, Francesca Meda, Edmond Dupont, Shahad Albadri, Nicole Quenech'Du, Eliane Ipendey, Michel Volovitch, Filippo Del Bene, Alain Joliot, Christine Rampon, Sophie Vriz (2016 May 10)

Hydrogen peroxide (H2O2) controls axon pathfinding during zebrafish development.

Developmental biology : 133-41 : DOI : 10.1016/j.ydbio.2016.05.004 Learn more
Summary

It is now becoming evident that hydrogen peroxide (H2O2), which is constantly produced by nearly all cells, contributes to bona fide physiological processes. However, little is known regarding the distribution and functions of H2O2 during embryonic development. To address this question, we used a dedicated genetic sensor and revealed a highly dynamic spatio-temporal pattern of H2O2 levels during zebrafish morphogenesis. The highest H2O2 levels are observed during somitogenesis and organogenesis, and these levels gradually decrease in the mature tissues. Biochemical and pharmacological approaches revealed that H2O2 distribution is mainly controlled by its enzymatic degradation. Here we show that H2O2 is enriched in different regions of the developing brain and demonstrate that it participates to axonal guidance. Retinal ganglion cell axonal projections are impaired upon H2O2 depletion and this defect is rescued by H2O2 or ectopic activation of the Hedgehog pathway. We further show that ex vivo, H2O2 directly modifies Hedgehog secretion. We propose that physiological levels of H2O2 regulate RGCs axonal growth through the modulation of Hedgehog pathway.

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Urs Lucas Böhm, Andrew Prendergast, Lydia Djenoune, Sophie Nunes Figueiredo, Johanna Gomez, Caleb Stokes, Sonya Kaiser, Maximilliano Suster, Koichi Kawakami, Marine Charpentier, Jean-Paul Concordet, Jean-Paul Rio, Filippo Del Bene, Claire Wyart (2016 Mar 8)

CSF-contacting neurons regulate locomotion by relaying mechanical stimuli to spinal circuits.

Nature communications : 10866 : DOI : 10.1038/ncomms10866 Learn more
Summary

Throughout vertebrates, cerebrospinal fluid-contacting neurons (CSF-cNs) are ciliated cells surrounding the central canal in the ventral spinal cord. Their contribution to modulate locomotion remains undetermined. Recently, we have shown CSF-cNs modulate locomotion by directly projecting onto the locomotor central pattern generators (CPGs), but the sensory modality these cells convey to spinal circuits and their relevance to innate locomotion remain elusive. Here, we demonstrate in vivo that CSF-cNs form an intraspinal mechanosensory organ that detects spinal bending. By performing calcium imaging in moving animals, we show that CSF-cNs respond to both passive and active bending of the spinal cord. In mutants for the channel Pkd2l1, CSF-cNs lose their response to bending and animals show a selective reduction of tail beat frequency, confirming the central role of this feedback loop for optimizing locomotion. Altogether, our study reveals that CSF-cNs constitute a mechanosensory organ operating during locomotion to modulate spinal CPGs.

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