RETROSPECTIVE CLONAL ANALYSIS OF THE CEREBELLUM USING GENETIC LAACZ LACZ MOUSE MOSAICS/

Analysis of lacZ neuronal clones in the mouse cerebellum demonstrates genealogical independence of the primary and secondary germinal epithe lia (PGE and SGE) from early development. PGE precursors and their neu ronal descendants are organised into two polyclonal groups of similar sizes that exhibit parasagittal patterning and generally respect the m idline. The relationship between these two groups cannot be traced bac k in time to less than 80 independent cells, which were probably recru ited following a period of non-coherent growth that distributes unrela ted cells into distinct territories of the neural tube. A lateromedial clonal organisation is observed in the mature cerebellum, suggesting the existence of many small parasagittal domains of clonal restriction and/or of cell dispersion in the rostrocaudal but not in the mediolat eral dimension. The organisation is orthogonal with respect to the cel lular organisation in the neural tube as is the genetic organisation. Cellular and genetic patterning of the cerebellum therefore share simi larities. A possible hypothesis is that distinct cell behaviours creat e the different clonal domains observed in this study and that the cel lular and genetic organisation of the cerebellum are coordinated.