Dynamic organization of developing Purkinje cells revealed by transgene expression.

The cerebellum has many properties that make it a useful model for investigating neural development. Purkinje cells, the major output neurons of the cerebellar cortex, have drawn special attention because of the availability of biochemical markers and mutants that affect their development. The spatial expression of L7, a protein specific for Purkinje cells, and L7 beta Gal, a gene expressed in transgenic mice that was constructed from the L7 promoter and the marker beta-galactosidase, delineated bands of Purkinje cells that increased in number during early postnatal development. Expression of the transgene in adult reeler mutant mice, which show inverted cortical lamination, and in primary culture showed that the initial expression of L7 is intrinsic to Purkinje cells and does not depend on extracellular signals. This may reflect an underlying developmental map in cerebellum.