The temporal and spatial expression patterns of mouse membrane palmitoylated protein 4 (Mpp4) gene was investigated. Mpp4 was expressed in postnatal but not embryonic retina by microarray analysis. Real-time quantitative RT-PCR analysis showed that, in addition to retina, Mpp4 was expressed at much lower levels in brain, heart, liver, and spleen tissues. In situ hybridization revealed that Mpp4 was exclusively localized in the photoreceptor cells. It was also detected in pineal gland but not other regions of the brain. Immunofluorescence labeling on eye sections of wild-type mice and transgenic mice with cone-specific GFP expression demonstrated that Mpp4 protein was localized at rod but not at cone photoreceptor synaptic terminals. The high level and cell-type specific expression of mouse Mpp4 gene makes it a good candidate for the targeting and assembly of specific molecules, such as calcium channels, at rod synaptic terminals. (C) 2003 Elsevier Science (USA). All rights reserved.