The centriolar complex isolated from starfish spermatozoa

Centrioles from spermatozoa of the starfish, Asterina pectinifera, were isolated and partially purified by solubilization of chromatin followed by sucrose density-gradient centrifugation. The ultrastructure of the isolated centriolar complex was investigated in whole mount preparations by electron microscopy. The complex unit was composed of a pair of centrioles and a pericentriolar structure, which associated with the distal end of the distal centriole by 9 spoke-like satellites extending radially to a marginal ring. Each satellite bifurcated at a dense node forming 2 fan-like shapes with a periodic striated pattern. The tubular structure of the centrioles easily disintegrated, leaving the pericentriolar structure or axonemal microtubules intact. The distal centriole in a spermatozoon served as an initiating site for flagellar microtubule assembly; that is, a number of "9 + 2' axonemal tubules were observed adhering just beneath the distal end of the basal body. In experiments in vitro, polymerization of microtubule proteins purified from porcine brain was initiated by the structure at the ends of both proximal and distal centrioles, but not from the satellites or the marginal ring. Also, few if any microtubules were formed from the sides of each centriole, even in the presence of a high concentration of exogenous tubulin. On the other hand, centrioles of spermatozoa, when they were in mature ooplasm, could initiate the formation of sperm asters by microtubules. Therefore, centrioles in spermatozoa seem to be able to initiate microtubules in a 2 ways. A possible explanation of the difference between the 2 types of microtubule organization in vivo, i.e. in the sperm cell itself and in the ooplasm, it discussed.

Polarity of microtubules nucleated by centrosomes and chromosomes of Chinese hamster ovary cells in vitro

The structural and growth polarities of centrosomal and chromosomal microtubules were studied by analyzing the kinetics of growth of these microtubules and those initiated by flagellar seeds. By comparing rates of elongation of centrosomal and flagellar-seeded microtubules, we determined whether the centrosomal microtubules were free to grow at their plus ends only, minus ends ony, or at both ends. Our results show that centrosomal microtubules elongate at a rate corresponding to the addition of subunits at the plus end only. The depolymerization rate was also equivalent to that for the plus end only. Chromosomal microtubule elongation was similar to the centrosome-initiated growth. Since the data do not support the hypothesis that both ends of these spindle microtubules are able to interact with monomer in solution, then growth must occur only distal or only proximal to the organizing centers, implying tha the opposite ends in unavailable for exchange of subunits. Experiments with flagellar-seeded microtubules serving as internal controls indicated that the inactivity of the minus end could not be accounted for by a diffusible inhibitor, suggesting a structural explanation. Since there is no apparent way in which the distal ends may be capped, whereas the proximal ends are embedded in the pericentriolar cloud, we conclude that centrosomal microtubules are oriented with their plus ends distal to the site of nucleation. A similar analysis for chromosomal microtubules suggests that they too must be oriented with their plus ends distal to the site of initiation.

Renal vein fibrin degradation products (FDP's) in glomerulonephritis

In order to determine the role of intrarenal vascular coagulation (IVC) in chronic glomerulonephritis, coagulant parameters in renal blood (RVB), urine FDP's and renal histology were examined in 70 patients with chronic glomerulonephritis (CGN). RVB was obtained by Seldinger's technique. A correlation was obtained between an increase of fibrinogen, FDP and soluble fibrin monomer complexes (SFMC) in RVB and the degree of intraglomerular fibrin deposition shown on immunofluorescence. An increase of FDP's, SFMC and a slight decrease of fibrinolytic activity in RVB were observed in patients with CGN with decreased renal function or with the nephrotic syndrome. Daily excretion of FDP in the urine and the extent of intraglomerular fibrin deposition were greater in nephrotics than in non-nephrotics. We conclude that measurement of coagulation parameters in RVB is a reliable and sensitive method of assessing IVC, and that IVC plays an important role in aggravation of chronic glomerulonephritis, particularly when the nephrotic syndrome is present.

Ultraviolet flow dichroism of brain microtubule

Ultraviolet flow dichroism of brain microtubule was measured. Large positive dichroisms were observed at 255 nm, 285 nm and 292 nm. The dichroism at about 255 nm is due to bound GDP or GTP. The dichroism at 285 nm is due to tyrosine and tryptophan residues, and that at 292 nm is due to the tryptophan residues of the protein. These results show that the electronic transition moments of nucleotides and aromatic groups are both nearly parallel to the polymer axis.

In vitro polymerization of flagellar and ciliary outer fiber tubulin into microtubules

About 10--20% of the total protein in the outer fiber fraction was solubilized by sonication in a solution containing 5 mM MES, 0.5 mM MgSO4, 1.0 mM EGTA, 1.0 mM GTP, and 0 or 50 mM KC1 at pH 6.7. The sonicated extract was shown by analytical centrifugation to consist largely of a 6 S component (tubulin dimer), having a molecular weight of 103,000, as determined by gel filtration, and possessing a colchicine-binding activity of 0.8 mole per tubulin dimer. The tubulin fraction failed to polymerize into microtubules by itself. Addition of a small amount of the ciliary outer fiber fragments or reconstituted short brain microtubules, however, induced polymerization, as demonstrated by viscosity of flow birefringence changes as well as light or electron microscopic observations. The growth of heterogeneous microtubules upon mixing outer fiber tubulin with DEAE-dextran-decorated brain microtubules was observed by electron microscopy. Microtubules were reconstituted from outer fiber tubulin without addition of any nuclei fraction when a concentrated tubulin fraction was warmed at 35degree. A few doublet-like microtubules or pairs of parallel singlet microtubules that were closely aligned longitudinally could be observed among many singlet microtubules. Unlike other fiber microtubules, the reconstituted polymers were depolymerized by exposure to Ca2+ ions, high or low ionic strength, colchicine, low temperature or SH reagents. No microtubules were assembled under these conditions.

Light-microscopic observations of individual microtubules reconstituted from brain tubulin

The course of polymerization of individual brain microtubules could be observed with a light microscope employing dark-field illumination. Statistical analysis of the increase in microtubule length during the polymerization was in accordance with the time course of viscosity change of the tubulin solution. After a plateau level in viscosity was attained, there was no significant change in histograms showing length distribution. These observations were confirmed with fixed and stained microtubules, using a phase-contrast microscope. Observations with dark-field illumination revealed that reconstituted microtubules depolymerized and disappeared immediately upon exposure to buffer containing CaCl2 or sulphydryl reagents such as p-chloromercuriphenyl sulphonic acid (PCMPS) and p-chloromercuribenzoic acid (PCMB). They were also cold-labile. The growth of heterogeneous microtubules which were assembled by mixing purified tubulin dimers with ciliary outer fibres could also be followed with these optical systems.

Electrophoretic separation of tubulin alpha and beta subunits after S-sulfonation

The modification of tubulin cystine and cystine residues to S-sulfocysteines caused a distinct separation of the alpha and beta subunits in a continuous sodium dodecyl sulfate polyacrylamide gel system. The well-separated subunit bands permitted investigation of the phosphorylation of alpha and beta tubulin subunits. The incubation of tubulin fraction with [gamma-32P]ATP demonstrated that both subunits were phosphorylated in vitro. The incorporation of 32-PO4 into sea urchin eggs, however, failed to cause phosphorylation of tubulin in vivo.