Developmental regulation of CPG15 expression in Xenopus

Mechanisms controlling dendritic arbor formation affect the establishment o f neuronal circuits. Candidate plasticity gene 15 (CPG15) is a glycosylphos phatidyl inositol (GPI)-linked activity-induced protein that has been shown to function as an intercellular signaling molecule that can promote the mo rphological and physiological development of the Xenopus retinotectal syste m. A thorough understanding of CPG15 function requires knowledge of the spa tiotemporal expression of the endogenous protein. We therefore cloned Xenop us cpg15 and used RNA in situ hybridization and immunohistochemistry to det ermine the pattern of CPG15 expression. cpg15 mRNA and CPG15 protein are fi rst detectable in the developing spinal cord and become widespread as devel opment proceeds. CPG15 is expressed in sensory regions of the brain, includ ing the visual, auditory, and olfactory systems. Within the retina, CPG15 i s only expressed in retinal ganglion cells. CPG15 protein is concentrated i n axon tracts, including retinal axons. These data support a model in which CPG15 expressed in retinal ganglion cells is trafficked to retinal axone, where it modulates postsynaptic dendritic arbor elaboration, and synaptic m aturation. (C) 2001 Wiley-Liss, Inc.