News and Publications

Cerebellar Development in Mice: Genetics, Cell Biology, and Gene Expression

C. Fletcher, M.E. Morrison, J.H. Wong

Our research goal is to understand the cell-cell interactions that lead to neuronal differentiation and synaptogenesis. We focus on the interrelated processes of the development of afferent fibers, dendrites, and spines in target neurons of the CNS. The cerebellum is an attractive model system because it has a limited number of cell types, many cell type--specific markers, and a regular architecture and wiring pattern. The cerebellum undergoes extensive development postnatally in rodents, providing a readily accessible experimental setting for studying neuronal migration, differentiation, and synaptogenesis. In addition, these processes are perturbed in a number of mutant mouse strains. We are using the tools of genetics, genomics, and cell biology to identify signal transduction pathways important for CNS neuronal survival, development, and synaptogenesis.

GENETIC APPROACHES

In collaboration with the Genomics Institute of the Novartis Research Foundation, La Jolla, California, we are using a genetic screen to detect new mouse mutants with abnormal cerebellar development.To date, 5 such deviants have been detected. Of these, the mutation in 1 strain is already mapped; that in a second strain is being mapped; and for the other 3 strains, probands are being made in preparation for mapping.

GENOMIC APPROACHES

We are using gene chips to obtain expression profiles of genes in the developing cerebellum. We are characterizing gene expression in the developing cerebellum in normal mice and are comparing the results with gene expression in strains of ataxic mice with mutations in known genes. In this way, we hope to gain insight into the signaling pathways necessary for normal cerebellar development and to identify targets for intervention in cerebellar ataxia.

CELL BIOLOGY APPROACHES

We are using primary neuron cultures to explore the cell-cell interactions necessary for the development of granule and Purkinje cells. Purified Purkinje cells survive and produce axons but no mature dendrites. Adding back the cerebellar granule cells, which form synapses with the Purkinje cells, triggers the development of dendrites and spines on the Purkinje cells, recapitulating the steps of differentiation seen in vivo. This culture system allows us to characterize the roles of specific signal transduction pathways in the interaction of granule and Purkinje cells. Preliminary results indicate that BDNF/TrkB signaling regulates the number and morphology of spines on Purkinje cells. We will use the same in vitro system to test other signaling systems identified by using the genetic and genomic approaches described.

PUBLICATIONS
Fletcher, C.F., Tottene, A., Lennon, V.A., Wilson, S.M., Dubel, S.J., Paylor, R., Hosford, D.A., Tessarollo, L., McEnery, M.W., Pietrobon, D., Copeland, N.G., Jenkins, N.A. Dystonia and cerebellar atrophy in Cacna1a null mice lacking P/Q channel activity. FASEB J. 15:1288, 2001.

Kawai, J., Shinagawa, A., Shibata, K., et al. The RIKEN Genome Exploration Research Group Phase II Team and the FANTOM Consortium. Functional annotation of a full-length mouse cDNA collection. Nature 409:685, 2001.

Nadeau, J.H., Balling, R., Barsh, G., Beier, D., Brown, S.D.M., Bucan, M., Camper, S., Carlson, G., Copeland, N., Eppig, J., Fletcher, C.F., Frankel, W.N., Ganten, D., Goldowitz, D., Goodnow, C., Guenet, J.L., Hicks, G., Hrabe de Angelis, M., Jackson, I., Jacob, H., Jenkins, N., Johnson, D., Justice, M., Kay, S., Kingsley, D., Lehrach, H., Magnuson, T., Meisler, M., Poustka, A., Rinchik, G., Rossant, J., Russell, L.B., Schimenti, J., Shiroishi, T., Skarnes, B., Soriano, P., Stanford, B., Takahashi, J., Wurst, W., Zimmer, A. Sequence interpretation: Functional annotation of mouse genome sequences. Science 291:1251, 2001.

Sharp, A.H., Fletcher, C.F., Sundarraj, S., Yunker, A.R., Dubel, S.J., Copeland, N.G., Jenkins, N.A., Copeland, T.D., McEnery, M.W. Convergent and coupled defects in voltage-dependent calcium channel subunit expression and distribution are revealed in hippocampi of ataxic and epileptic mice. J. Neurosci., in press.

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