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 members contain four potential calcium-binding domains commonly referred to as "EF-hand motifs". VILIP interacts in a calcium-dependent manner with the actin-based neuronal cytoskeleton and modulates the phosphorylation of G-protein-coupled receptors, i.e., rhodopsin, in vitro. Here, we have used antisera against VILIP to study its distribution in the chick brain. Immunostaining of subsets of neurons is observed throughout the brain. Generally, the distribution of VILIP coincides well with the distribution of VILIP transcripts as detected previously by in situ hybridization. The most intense expression is detected in the visual system and the cerebellum. In the visual system, neurons of the nuclei of the ascending tecto-fugal pathway are stained, as are the pretectal, isthmic, and oculomotor nuclei. VILIP immunoreactivity is found in cell bodies, dendrites, and synaptic structures. Thus, VILIP appears to be an excellent marker for the characterization of neurons of the visual pathway. In the cerebellum, VILIP immunoreactivity is detected in deep cerebellar nuclei and in a subset of granule cells, Golgi type II cells, basket cells, and stellate cells, whereas it is completely absent from Purkinje cells. Intense punctate staining in the molecular layer suggests that VILIP is transported from deep cerebellar nuclei and from granule cells to the glutamatergic climbing-fiber and parallel-fiber synapses, respectively, both of which terminate on Purkinje-cell dendrites. The localization of VILIP in these presynaptic terminals has been confirmed at the electron-microscopic level.