Cône de croissance

Image d'un cône de croissance marqué montrant des microtubules (vert) et des fibres d'actine (rouge)

Un cône de croissance est une extension dynamique, riche en actine, d'un neurite en développement cherchant un organe cible. Il se situe à l'extrémité distale d'un prolongement axonal ou dendritique neuroblastique en croissance « s'étendant sur des distances considérables suivant souvent des chemins complexes pour atteindre leurs organes cibles (muscles, glandes, récepteurs sensitifs, ou encore synapses avec d'autres neurones) situés en dehors du système nerveux central »[1].

Structure et fonctions

Cellules de crêtes neurales en culture in vitro en train de migrer grâce à leurs lamellipodes.

Il s'agit d'une structure cellulaire transitoire et mobile, qui a pour fonction d'explorer l'environnement extracellulaire et de répondre au guidage axonal assuré par différentes molécules[2].

Les protéines de guidage indiquent au cône de croissance sa voie de migration[3] en modifiant la vitesse ou la direction de sa croissance par une biosynthèse des protéines adaptée[4]. Il existe 2 catégories de molécules sécrétées par les cellules cibles :

  • Les protéines chimioattractives qui attirent à distance le cône de croissance.
  • Les protéines chimiorépulsives qui repoussent à distance le cône de croissance.

Les différentes molécules de guidage sont :

Les protéines d'adhésion cellulaire sont aussi impliquées dans ce processus[5].

Les protéines Wnt[6] et les sonic hedgehog[7] seraient aussi concernées.

L'extrémité du cône de croissance est composée de feuillets membranaires aplatis, les lamellipodes desquels partent les filopodes, de fins prolongements contenant des microfilaments d'actine et de myosine, qui s'allongent puis se rétractent rythmiquement[1],[8].

Dès que le cône de croissance atteint l'organe cible, son cytosquelette subit des modifications. Le cône forme alors une synapse et la croissance de l'axone s'arrête[9].

Notes et références

  1. ↑ a et b « Croissance axonale vers les cellules cibles: les cônes de croissance », Universités de Fribourg, Lausanne et Berne (Suisse).
  2. ↑ (en) Marc Tessier-Lavigne, Corey S. Goodman, « The Molecular Biology of Axon Guidance », Science, vol. 274, no 5290,‎ , p. 1123-1133 (DOI 10.1126/science.274.5290.1123, résumé).
  3. ↑ (en) Harris, W.A., Holt, C.E., and Bonhoeffer, F., « Retinal axons with and without their somata, growing to and arborizing in the tectum of Xenopus embryos: a time-lapse video study of single fibres in vivo », Development, vol. 101,‎ , p. 123–133 (lire en ligne [PDF]).
  4. ↑ (en) Yoo, S; van Niekerk EA, Merianda TT, Twiss JL., « Dynamics of axonal mRNA transport and implications for peripheral nerve regeneration », Experimental Neurology, vol. 1, no 223,‎ , p. 19-27 (DOI 10.1016/j.expneurol.2009.08.011, lire en ligne).
  5. ↑ S. Mark Williams (trad. de l'anglais par Jean-Marie Coquery), Sylvius : atlas du système nerveux central humain, Paris, De Boeck, , 727 p. (ISBN 2-7445-0161-1, lire en ligne).
  6. ↑ D. C. Lie, S. A. Colamarino, H. J. Song, L. Desire, H. Mira, A. Consiglio, E. S. Lein, S. Jessberger, H. Lansford, A. R. Dearie and F. H. Gage (2005) "Wnt signalling regulates adult hippocampal neurogenesis" in Nature Volume 437, pages 1370-1375.
  7. ↑ Echelard Y, Epstein DJ, St-Jacques B, Shen L, Mohler J, McMahon JA, McMahon AP, « Sonic hedgehog, a member of a family of putative signaling molecules, is implicated in the regulation of CNS polarity », Cell, vol. 75, no 7,‎ décember 1993, p. 1417–30 (PMID 7916661, DOI 10.1016/0092-8674(93)90627-3)
  8. ↑ [PDF]Cramer, Louise P. Molecular Mechanism of Actin-Dependent retrograde Flow in Lamellipodia of Motile Cells. Frontiers in Bioscience, 2, d260-270,
  9. ↑ Dale Purves (trad. de l'anglais par Jean-marie Coquery), Neurosciences, Bruxelles, De Boeck Supérieur, , 3e éd., 840 p. (ISBN 2-8041-4797-5 et 9782804147976, lire en ligne).

Voir aussi

Articles connexes

Liens externes


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Développement du système nerveux
Général
Anatomie
Gènes et voies de signalisation
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