Our results unravelled that, during embryonic development, the corpus callosum (CC) is populated in addition to astroglia by numerous glutamatergic and GABAergic guidepost neurons that are essential for the correct midline crossing of callosal axons. Based on these data, we aim to study in details the dynamic aspects of these processes by confocal time-lapse video microscopy, as well as, the cellular and molecular aspects of the guidance mechanisms involved in the establishment of this axonal pathway. First, we will have a look at the origin and the identity of the CC guidepost neurons using in vitro and in vivo cell fate mapping experiments. To determine the molecular basis of the guidance mechanisms we will study in details the expression profile of CC neurons for guidance cues. To this hand, an extensive screen for genes of interest will be perform using a very sensitive RT-PCR technique, microarray chips, as well as, in situ hybridization. The contribution of candidate genes to callosal axon guidance will be test by combining in vitro and in vivo analysis. Finally, we will investigate the potential implication of these transient neurons in agenesis of the CC which occurs in numerous human congenital syndromes.

• Lebrand, C., Cases, O., Aldebrecht, C., Doye, A., Alvarez, C., El Mestikawy, S., Seif, I. and Gaspar, P. Transient uptake and storage of serotonin in developing thalamic neurons. Neuron, 1996, 17, 823-835.

• Lebrand, C., Cases. O., Wehrlé, R,  Cases, O.,  Blakely, R.D., Edouards,.R.H. and Gaspar, P. Transient developmental expression of monoamine transporters in the rodent forebrain. Journal of  Comparative Neurology, 1998, 4, 506-24.

• Cases, O., Lebrand, C., Giros, B., Vitalis, T., Price, D.J., Gaspar, P., and Seif, I. Plasma membrane transporters of serotonin, dopamine, and norepinephrine mediate serotonin accumulation in atypical locations in the developing brain of monoamine oxidase A knock-outs. Journal of Neuroscience, 1998, 18, 6914-27.

• Upton, A.L., Salichon, N., Lebrand, C., Seif, I. and Gaspar, P. Excess of serotonin (5-HT) alters the segregation of ispilateral and contralateral retinal projections in monoamine oxidase A knock-out mice:possible role of 5-HT uptake in retinal ganglion cells during development. Journal of  Neuroscience, 1999, 19, 7007-24.

• Lebrand, C., Michela C., Goodson H., Cosson P., Cavalli V., Mayran N., Faure J., and Gruenberg, J. Late endosome motility depends on lipids via the small GTPase Rab7. EMBO Journal, 2002, 21, 1289-1300.

• Lebrand C., Dent E.W., Strasser G, Lanier L.M., Krause M, T. M. Svitkina, G. G. Borisy, and Gertler F.B. Critical role of Ena/VASP proteins for filopodia formation in neurons and in function downstream of Netrin-1. Neuron, 2004, 42, 37–49.

·         Lebrand C, Gaspar P., and Hornung J-P. Transitory uptake of serotonin in the developing sensory pathways of the common marmoset. Journal of Comparative Neurology,  2006, 499(4):677-89.

• Dwivedy A., Gertler  F., Miller J., Holt C, and Lebrand C. Ena/VASP function in Retinal Axons is required for Terminal Arborization but not Pathway Navigation. Development, 2007, 134(11):2137-46.

• Niquille M., Garel S., Mann F., Hornung J-P._, Otsmane B., Chevalley S., Parras C.,  Guillemot F., Gaspar P., Yanagawa Y., and Lebrand C. Transient neuronal populations are required to guide callosal axons: A role for semaphorin3C. Accepted in PLoS Biology.

Cell and organotypic culture,
in vitro electroporation technics,
Histology,
Confocal imaging
Time-laps imaging