Electrophoretic analysis of basal body (centriole) proteins

Heat shock causes protein aggregation and reduced protein solubility at the centrosome and other cytoplasmic locations

Heat shock markedly inhibited centrosome staining by antisera raised against the two centrosome-specific proteins, pericentrin and gamma tubulin. The inhibition of anti-pericentrin binding was measured by fluorescence imaging. Heat had the greatest effect on intact cells, followed in sensitivity by centrosomes attached to their companion nucleus, with purified centrosomes being least sensitive. The centrosomal content of pericentrin was measured by immunoprecipitation followed by western blotting. Heat caused the amount of pericentrin in the centrosomal fraction to increase, suggesting that pericentrin did not leave the centrosome during heat shock. Furthermore, the pericentrin of the centrosomal fraction became less soluble after heat shock, and could only be solubilized by the most denaturing condition of boiling in 0.1% SDS. Immunoelectron microscopy revealed a heat-induced increase in the electron-dense material comprising the pericentriolar material (PCM), consistent with protein aggregation. Lastly, in heated cells immunoelectron microscopy demonstrated an increase in the binding of heat shock protein 70 (HSP70) to numerous locations throughout the cytoplasm. These data suggest that heat shock reduces the solubility of centrosomal and other cytoplasmic proteins, most likely through protein aggregation.

Characteristics of basal body cartwheel reassembly

Cartwheel complexes reassembled in a fraction derived by treating isolated oral apparatuses from Tetrahymena with 1.0 M KCl for 12 h. Approximately 40% of the KCl-soluble protein reassembled into cartwheel complexes. The reassembly reaction was protein-concentration dependent, and reassembled cartwheels were stable at 3 degrees C. Sucrose gradient centrifugation resolved 3 high molecular mass protein complexes from the KCl-soluble fraction. Each of the 3 complexes has a different mass, but each contains the same 5 polypeptides, 2 of which are probably tubulins. When these complexes were removed from the KCl-soluble fraction by high speed centrifugation, cartwheel reassembly did not occur. The 5 polypeptides in the high molecular mass complexes were among several other polypeptides resolved from reassembled cartwheels by 2-dimensional gel electrophoresis. The high molecular mass complexes are probably essential for cartwheel formation. The electrophoretic data also show that several polypeptides in the KCL-soluble fraction do not appear to be incorporated into cartwheels. These polypeptides are probably non-essential for cartwheel formation.

Cytoskeletal architecture and immunocytochemical localization of fodrin in the terminal web of the ciliated epithelial cell

In order to understand the cytoskeletal architecture at the terminal web of the ciliated cell, we examined chicken tracheal epithelium by quick-freeze deep-etch (QFDE) electron microscopy combined with immunocytochemistry of fodrin. At the terminal web, the cilia ended into the basal bodies and then to the rootlets. The rootlets were composed of several filaments and globular structures attached regularly to them. Decoration with myosin subfragment 1 (S1) revealed that some actin filaments ran parallel to the apical plasma membrane between the basal bodies, and other population traveled perpendicularly or obliquely, i.e., along the rootlets. Some actin filaments were connected to the surface of the basal bodies and the basal feet. Among the basal bodies and the rootlets there existed three kinds of fine crossbridges, which were not decorated with S1. In the deeper part of the terminal web, intermediate filaments were observed between the rootlets and were sometimes crosslinked with the rootlets. Immunocytochemistry combined with the QFDE method revealed that fodrin was a component of fine crossbridges associated with the basal bodies. We concluded that an extensive crosslinker system among the basal bodies and the rootlets along with networks of actin and intermediate filaments formed a structural basis for the effective beating of cilia.

A novel mitotic spindle pole component that originates from the cytoplasm during prophase

Several unique aspects of mitotic spindle formation have been revealed by investigation of an autoantibody present in the serum of a patient with the CREST (calcinosis, Raynaud's phenomenon, esophageal dysmotility, schlerodacytyly, and telangiectasias) syndrome. This antibody was previously shown to label at the spindle poles of metaphase and anaphase cells and to be absent from interphase cells. We show here that the serum stained discrete cytoplasmic foci in early prophase cells and only later localized to the spindle poles. The cytoplasmic distribution of the antigen was also seen in nocodazole-arrested cells and prophase cells in populations treated with taxol. In normal and taxol-treated cells, the microtubules appeared to emanate from the cytoplasmic foci and polar stain, and in cells released from nocodazole block, microtubules regrew from antigen-containing centers. This characteristic distribution suggests that the antigen is part of a microtubule organizing center. Thus, we propose that a prophase originating polar antigen functions in spindle pole organization as a coalescing microtubule organizing center that is present only during mitosis. Characterization of the serum showed reactions with multiple proteins at 115, 110, 50, 36, 30, and 28 kD. However, affinity-eluted antibody from the 115/110-kD bands was shown to specifically label the spindle pole and cytosolic foci in prophase cells.

Identification of centrosomal proteins in a human lymphoblastic cell line

Highly enriched preparations of centrosomes from human T-lymphoblasts KE 37 were analyzed for their protein content. The specific pattern of polypeptides was characterized by an abundant subset of high mol. wt proteins and a major group of proteins with mol. wt ranging from 50 to 65 kd. Several immunoreactive proteins were identified, using a rabbit serum spontaneously reacting with human centrosomes. They include a family of high mol. wt ranging from 180 to 250 kd, a 130-kd protein and a 60-65 kd doublet. These antigens have the following properties: they are localized within the pericentriolar material; their abundance, as judged by centrosome labelling, changes significantly during the cell cycle, the maximum being observed at the pole of the metaphasic spindle; in Taxol-treated cells where the centrosome is no longer acting as a nucleating center, they redistribute at one end of the microtubule arrays in both mitotic and interphasic cells, as expected for nucleating, or capping, proteins. All these properties are compatible with their involvement in microtubule nucleation.

The centriolar rim. The structure that maintains the configuration of centrioles and basal bodies in the absence of their microtubules

Preparations of centrioles from bovine spleen were incubated in solutions of NaCl, MgCl2, HCl, NaOH, EDTA and heparin. Their effects on the centrioles were studied by electron microscopy of ultrathin sections. It was found that the microtubules of centriolar cylinders gradually disintegrate at a higher than physiological ionic strength and at a pH value lower than 3.5 and higher than 8.5. After microtubule extraction, a closely apposed rim or sheath of dense centriolar matrix remains which has the same dimensions of length and width as the original centriole. Some other centriolar structures, including the pericentriolar satellites and certain structures in the cylinders (hub) are also preserved. The basal bodies of fish spermatozoa revealed similar structures, including the centriolar rim and hub, after microtubule extraction. Thus, the microtubule triplets are not involved in maintaining the structure of the centriolar cylinder; this role is rather carried out by amorphous material--the matrix, surrounding the microtubules.

A protein of 175,000 daltons associated with striated rootlets in ciliated epithelia, as revealed by a monoclonal antibody

Basal bodies from laying quail oviduct were semipurified and used as immunogen to produce monoclonal antibodies. On 38 clones obtained and among those staining the apical pole of the ciliated cell, CC-310 was chosen because it labeled the apical region with a punctuated aspect, suggesting a staining of basal bodies or of basal body-associated structures; the basal pole was also labeled. The ultrastructural localization performed by the immunogold technique showed that the labeling was mainly associated with the striated rootlets. The basal feet, the side of the basal bodies, and the basal poles of the demembranated cells were also decorated. The identification of the antigen performed by immunoblots of deciliated cortices revealed two proteins of 175,000 and 40,000, whereas immunoblots of basal bodies showed only the 175,000-mw protein. The possibility of these two proteins sharing the same epitope, located at both poles of the cell, is discussed. Immunofluorescence ascertained that CC-310 decorated the striated rootlets in ciliated epithelia from other species: mussel, frog, and human tissue. Finally, when tested on cultured cell lines, CC-310 labeled the centrosome and its associated rootlets on PtK2 during interphase. During mitosis the poles of the mitotic spindle were stained without any apparent rootlet-like structure.

Centriole size modifications during the cell cycle of the amoebae of the mxyomycete Physarum polycephalum

Anterior and posterior centrioles of Physarum amoebae are indistinguishable by their size during interphase but there is a correlation between the size of the two centrioles in the same amoeba. The interphase length of centrioles in diploid amoebae possessing only one pair of centrioles was 11% longer than in the case of the haploid strain. Treatment with taxol led to a 23 and 32% increase of the mean length in interphase and blocked mitosis, respectively. Conversely, during control mitosis the parental centrioles showed a 12% decrease of their mean length while the size of the daughter centrioles increased progressively. Neither nocodazole nor cold treatment induce a decrease of centriole length. The mean length of the cartwheel structure (internal proximal part) although constant during mitosis could be increased 24% in the presence of taxol. Similarly there was a correlation between the number of anterior satellites and the centriole length.

Isolation of newt lung ciliated cell models: characterization of motility and coordination thresholds

Demembranated ciliated cell models are useful for studying mechanisms responsible for the regulation of ciliary coordination and waveform. This paper describes procedures for isolating ciliated cells from the newt, Taricha granulosa, by trypsin dissociation, their subsequent demembranation by Triton X-100, and their reactivation with MgATP to produce highly motile, coordinated, ciliated cell models. Reactivation of cell models with a high degree of mechanochemical coupling depended on avoiding mechanical damage and maintaining optimal conditions during all stages of isolation and reactivation. Highly motile models were prepared from cells incubated in trypsin, treated briefly with EDTA, separated by gentle agitation, and concentrated by centrifugation at low gravitational forces. Optimal demembranation and reactivation conditions were similar to those described previously for isolated newt lung axonemes. Under these conditions, nearly 100% of the models were reactivated when provided with MgATP and 90-95% beat with coordinated waves. The ciliary tufts beat at frequencies within the range measured in living cells and their reactivated motility was stable for at least 30 min at constant MgATP. These highly coupled models were used to show (1) that development of coordination in the ciliary tuft occurs at a higher substrate concentration range (10-25 microM) than that required to initiate motility per se (2-10 microM; (2) that outer dynein arms may not contribute to beat frequency at substrate concentrations below 35 microM; and (3) that vanadate has effects both on beat frequency and coordination of the tufts.

The control of anthozoan cilia by the basal apparatus

The ciliary basal apparatus in the pharynx of the sea anemone, Calliactis parasitica (Couch), is composed of two centrioles, a single striated rootlet at least 20 microns long, and a basal foot, to the tip of which is attached a bundle of microtubules leading to the rootlet. When the basal apparatus is sectioned in the plane of the ciliary power-stroke, the distal centriole, with which the cilium base is continuous, is rarely found to be erect. The orientation of the distal centriole is determined by bending in the basal apparatus. Bending occurs only in the plane of the ciliary power-stroke towards the side from which the basal foot projects, and it is closely correlated with membrane buckling in the belt desmosome region of the cell apex. Associated with the belt desmosome, but not directly with the basal apparatus, are bundles of filaments. These filaments are of two size classes, 5-6 and 10 nm in diameter. A model is presented in which the 5-6 nm filaments form the basis of a contractile system which mediates membrane buckling in the region of the belt desmosome. This action effectively shortens the cell apex and thus forces the apparatus to bend. The precise reorientation of the distal centriole is a result of the mechanical properties of the basal apparatus.