LOCALIZATION OF THE NEURAL CALCIUM-BINDING PROTEIN VILIP (VISININ-LIKE PROTEIN) IN NEURONS OF THE CHICK VISUAL-SYSTEM AND CEREBELLUM

The visinin-like protein (VILIP) is a member of a recently discovered family of calcium sensors specifically expressed in neurons. Family me mbers contain four potential calcium-binding domains commonly referred to as ''EF-hand motifs''. VILIP interacts in a calcium-dependent mann er with the actin-based neuronal cytoskeleton and modulates the phosph orylation of G-protein-coupled receptors, i.e., rhodopsin, in vitro. H ere, we have used antisera against VILIP to study its distribution in the chick brain. Immunostaining of subsets of neurons is observed thro ughout the brain. Generally, the distribution of VILIP coincides well with the distribution of VILIP transcripts as detected previously by i n situ hybridization. The most intense expression is detected in the v isual system and the cerebellum. In the visual system, neurons of the nuclei of the ascending tecto-fugal pathway are stained, as are the pr etectal, isthmic, and oculomotor nuclei. VILIP immunoreactivity is fou nd in cell bodies, dendrites, and synaptic structures. Thus, VILIP app ears to be an excellent marker for the characterization of neurons of the visual pathway. In the cerebellum, VILIP immunoreactivity is detec ted in deep cerebellar nuclei and in a subset of granule cells, Golgi type II cells, basket cells, and stellate cells, whereas it is complet ely absent from Purkinje cells. Intense punctate staining in the molec ular layer suggests that VILIP is transported from deep cerebellar nuc lei and from granule cells to the glutamatergic climbing-fiber and par allel-fiber synapses, respectively, both of which terminate on Purkinj e-cell dendrites. The localization of VILIP in these presynaptic termi nals has been confirmed at the electron-microscopic level.