Centriolar satellites: Molecular characterization, ATP-dependent movement toward centrioles and possible involvement in ciliogenesis

We identified Xenopus pericentriolar material-1 (PCM-1), which had been rep orted to constitute pericentriolar material, cloned its cDNA, and generated a specific pAb against this molecule. Immunolabeling revealed that PCM-1 w as not a pericentriolar material protein, but a specific component of centr iolar satellites, morphologically characterized as electron-dense granules, similar to 70-100 nm in diameter, scattered around centrosomes. Using a GF P fusion protein with PCM-1, we found that PCM-l-containing centriolar sate llites moved along microtubules toward their minus ends, i.e., toward centr osomes, in live cells, as well as in vitro reconstituted asters. These find ings defined centriolar satellites at the molecular level, and explained th eir pericentriolar localization. Next, to understand the relationship betwe en centriolar satellites and centriolar replication, we examined the expres sion and subcellular localization of PCM-1 in ciliated epithelial cells dur ing ciliogenesis. When ciliogenesis was induced in mouse nasal respiratory epithelial cells, PCM-1 immunofluorescence was markedly elevated at the api cal cytoplasm. At the electron microscopic level, anti-PCM-1 pAb exclusivel y labeled fibrous granules, but not deuterosomes, both of which have been s uggested to play central roles in centriolar replication in ciliogenesis. T hese findings suggested that centriolar satellites and fibrous granules are identical novel nonmembranous organelles containing PCM-1, which may play some important role(s) in centriolar replication.