PCM1

Abstract: We identified Xenopus pericentriolar material-1 (PCM-1), which had been reported to constitute pericentriolar material, cloned its cDNA, and generated a specific pAb against this molecule. Immunolabeling revealed that PCM-1 was not a pericentriolar material protein, but a specific component of centriolar satellites, morphologically characterized as electron-dense granules, ∼70–100 nm in diameter, scattered around centrosomes. Using a GFP fusion protein with PCM-1, we found that PCM-1–containing centriolar satellites moved along microtubules toward their minus ends, i.e., toward centrosomes, in live cells, as well as in vitro reconstituted asters. These findings defined centriolar satellites at the molecular level, and explained their pericentriolar localization. Next, to understand the relationship between centriolar satellites and centriolar replication, we examined the expression and subcellular localization of PCM-1 in ciliated epithelial cells during ciliogenesis. When ciliogenesis was induced in mouse nasal respiratory epithelial cells, PCM-1 immunofluorescence was markedly elevated at the apical cytoplasm. At the electron microscopic level, anti–PCM-1 pAb exclusively labeled fibrous granules, but not deuterosomes, both of which have been suggested to play central roles in centriolar replication in ciliogenesis. These 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.

Abstract: We report the identification and primary sequence of PCM-1, a 228-kD centrosomal protein that exhibits a distinct cell cycle-dependent association with the centrosome complex. Immunofluorescence microscopy using antibodies against recombinant PCM-1 demonstrated that PCM-1 is tightly associated with the centrosome complex through G1, S, and a portion of G2. However, late in G2, as cells prepare for mitosis, PCM-1 dissociates from the centrosome and then remains dispersed throughout the cell during mitosis before re-associating with the centrosomes in the G1 phase progeny cells. These results demonstrate that the pericentriolar material is a dynamic substance whose composition can fluctuate during the cell cycle.

Abstract: Context A role for the centrosome has been suggested in the pathology of major mental illnesses, especially schizophrenia (SZ). Objectives To show that pericentriolar material 1 protein (PCM1) forms a complex at the centrosome with disrupted-in-schizophrenia 1 (DISC1) and Bardet-Biedl syndrome 4 protein (BBS4), which provides a crucial pathway for cortical development associated with the pathology of SZ. To identify mutations in the PCM1 gene in an SZ population. Design Interaction of DISC1, PCM1, and BBS proteins was assessed by immunofluorescent staining and coimmunoprecipitation. Effects of PCM1, DISC1, and BBS on centrosomal functions and corticogenesis in vivo were tested by RNA interference. The PCM1 gene was examined by sequencing 39 exons and flanking splice sites. Setting Probands and controls were from the collection of one of us (A.E.P.). Patients Thirty-two probands with SZ from families that had excess allele sharing among affected individuals at 8p22 and 219 white controls. Main Outcome Measures Protein interaction and recruitment at the centrosome in cells; neuronal migration in the cerebral cortex; and variant discovery in PCM1 in patients with SZ. Results PCM1 forms a complex with DISC1 and BBS4 through discrete binding domains in each protein. DISC1 and BBS4 are required for targeting PCM1 and other cargo proteins, such as ninein, to the centrosome in a synergistic manner. In the developing cerebral cortex, suppression of PCM1 leads to neuronal migration defects, which are phenocopied by the suppression of either DISC1 or BBS4 and are exacerbated by the concomitant suppression of both. Furthermore, a nonsense mutation that segregates with SZ spectrum psychosis was found in 1 family. Conclusions Our data further support for the role of centrosomal proteins in cortical development and suggest that perturbation of centrosomal function contributes to the development of mental diseases, including SZ.

Abstract: Defects in centrosome and cilium function are associated with phenotypically related syndromes called ciliopathies. Centriolar satellites are centrosome-associated structures, defined by the protein PCM1, that are implicated in centrosomal protein trafficking. We identify Cep72 as a PCM1-interacting protein required for recruitment of the ciliopathy-associated protein Cep290 to centriolar satellites. Loss of centriolar satellites by depletion of PCM1 causes relocalization of Cep72 and Cep290 from satellites to the centrosome, suggesting that their association with centriolar satellites normally restricts their centrosomal localization. We identify interactions between PCM1, Cep72, and Cep290 and find that disruption of centriolar satellites by overexpression of Cep72 results in specific aggregation of these proteins and the BBSome component BBS4. During ciliogenesis, BBS4 relocalizes from centriolar satellites to the primary cilium. This relocalization occurs normally in the absence of centriolar satellites (PCM1 depletion) but is impaired by depletion of Cep290 or Cep72, resulting in defective ciliary recruitment of the BBSome subunit BBS8. We propose that Cep290 and Cep72 in centriolar satellites regulate the ciliary localization of BBS4, which in turn affects assembly and recruitment of the BBSome. Finally, we show that loss of centriolar satellites in zebrafish leads to phenotypes consistent with cilium dysfunction and analogous to those observed in human ciliopathies.