News and Publications

Cerebellar Development in the Mouse: Genetics, Cell Biology, and Gene Expression

C.F. 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 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 and a regular architecture and wiring pattern. The cerebellum undergoes extensive development postnatally in rodents, providing an accessible experimental setting for studying neuronal migration, differentiation, and synaptogenesis. In addition, these processes are perturbed in a number of mutant mouse strains.

GENETIC AND GENOMIC APPROACHES

In collaboration with the Genomics Institute of the Novartis Research Foundation, San Diego, California, we using a genetic screen to detect new mouse mutants with abnormal cerebellar development. We are also 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 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 that occur in vivo. Using this culture system, we can characterize the roles of specific signal transduction pathways in the interaction of granule and Purkinje cells. Preliminary data indicated that BDNF/TrkB signaling regulates the number and morphology of spines on Purkinje cells and that DCC/netrin signaling regulates the outgrowth of dendrites. We will use the same in vitro system to test other signaling systems identified in the genetic and genomic approaches described. We are also developing methods for efficient gene transfer into Purkinje and granule cells in vitro.

The combination of these approaches gives us new and exciting ways to identify the signal transduction pathways important for the survival, development, and synaptogenesis of neurons in the CNS.

PUBLICATIONS

Dupuy, A.J., Clark, K., Carlson, C.M., Fritz, S., Davidson, A.E., Markley, K.M., Finley, K., Fletcher, C.F., Ekker, S.C., Hackett, P.B., Horn, S., Largaespada, D.A. Mammalian germ-line transgenesis by transposition. Proc. Natl. Acad. Sci. U. S. A. 99:4495, 2002.

Matesic, L.E., Yip, R., Reuss, A.E., Swing, D.A., O'Sullivan, T.N., Fletcher, C.F., Copeland, N.G., Jenkins, N.A. Mutations in Mlph, encoding a novel member of the Rab effector family, cause the melanosome transport defects observed in leaden mice. Proc. Natl. Acad. Sci. U. S. A. 98:10238, 2001.