Expression of Rho GTPases Rho-A and Rac1 in the adult and developing gerbil cerebellum.

Rho GTPases proteins are essential for cytoskeletal reorganization and play important roles in the development of neuronal dendrites and axons. Several studies have implicated two members of the Rho GTPase family Rho-A and Rac1 activities in the neuronal polarization and the formation of axons and dendrites. In order to correlate cellular expressions of Rho-A and Rac1 with neuronal polarity (axons versus dendrite formation) in the central nervous system, the cerebellum and immunochemical techniques have been chosen. In the adult cerebellar cortex differential pattern of distribution between Rho-A and Rac1 was observed. While Rac1 expression was restricted to Purkinje cell (somata, dendrites and axons), Rho-A was ubiquitously distributed within the cerebellar cortex. Rac1 was localized in the Purkinje cell dendritic arborization (largest and tiny dendrites) and in their axons. This pattern of distribution was also observed during the postnatal development and followed the dendritic morphogenesis of Purkinje cell. Rho-A was highly expressed in the adult Purkinje cells somata, in cells of the granular layer, in glia within the white matter and in axons. Intense staining was observed in Bergmann glia cell bodies and processes. In the developing cerebellum, Rho-A was highly present in cells of the external and internal granule layers and in the Purkinje cell layer. Bergmann glia cell bodies and processes had the most intense staining during the development. The present study reveals a high expression of Rac1 and Rho-A during Purkinje cell neurites outgrowth period which occurred after birth in the cerebellum. In addition Rho-A is highly expressed in granule cell progenitor cells present in the external granular layer and therefore may play an important role in granule cell progenitor migration.