A 70 kDa microtubule-associated protein in NIL8 cells comigrates with the 70 kDa heat shock protein

When eukaryotic cells are exposed to environmental stress such as elevated temperature, the synthesis of heat shock proteins (HSP) is stimulated. We have raised a monoclonal antibody to a 70 kDa cytoskeleton-associated protein; this antibody also appears to recognize HSPs 68, 70 and 90, as well as an additional 40 kDa non-heat shock protein. We have used this monoclonal antibody to study the localization of the 70 kDa protein in the cytoskeletons of NIL8 hamster fibroblasts. By selective sequential solubilization of the components of NIL8 cells and analysis of the resulting cytoskeletal preparations by Western blot technique and indirect immunofluorescence, we have shown that the 70 kDa protein is associated with microtubules in mitotic and interphase cells and comigrates with HSP70 on 2-dimensional gel electrophoretigrams.     

Electron Microscopic Study of Trypanosoma cruzi Periplast in Tissue Cultures. I. Number and Arrangement of the Peripheral Microtubules in the Various Forms of the Parasite's Life Cycle*

SYNOPSIS. In an electron microscopic study, counts of peripheral microtubules were made in spheromastigotes and trypomastigotes in tissue cultures of embryonic heart muscle cells. In interphase spheromastigotes there were, at the level of the nucleus, ～ 114 microtubules; in dividing forms, there were ～ 222. In trypomastigotes, the number of microtubules varied according to the level of the section—there were fewer than 40 tubules in the pointed ends of an organism, while in the central segment the number of these elements ranged from 60 to 115. The highest number of microtubules was found in the region containing the Golgi complex. The distance between the microtubules was constant, equalling 44 nm, even at the pointed ends of a trypanosome. This suggests that the microtubules course parallel to one another. Cross sections and randomly arranged, variable length, longitudinal sections of the tubules were noted around the kinetosomes in dividing organisms.     

Apical Growth in Algae

Cytological and physiological aspects of apical growth in algae are reviewed. Data on morphology and ultrastructural organization of siphonous thalli are presented. Special attention is paid to the organization of microtubules and microfilaments and the role of the cytoskeleton in morphogenesis. A comparative study of apical growth in algae, fungi, and higher plants is presented.     

High cytotoxicity and membrane permeability of Et3Pb+ in mammalian and plant cells

Cells of mammalian origin as well as those of higher plants appear to be very sensitive to triethyllead ion (Et₃Pb⁺). Neuroblastoma cells kept in the presence of 1 μM Et₃Pb⁺ lost their viability within 6 h. Growth of suspension culture cells of soybean (G. max(L.)Merr.) was inhibited by 1 μM Et₃Pb⁺, and finally the cells died. Morphologically, Et₃Pb⁺ caused the complete breakdown of microtubular structures in neuroblastoma cells; thus microtubules appeared to be the main target for the toxin. While in a previous study the effect of Et₃Pb⁺ on microtubules has been well documented at concentrations of 50–200 μM ¹, the present study demonstrates that the formation of microtubules from pig brain tubulin is disturbed at concentrations of Et₃Pb⁺ as low as 0.5 to 1 μM . We conclude from these data that Et₃Pb⁺ freely permeates the plasma membranes of mammalian as well as plant cells.     

Fine structural aspects of silk secretion in a spider. II. Conduction in the pyriform glands

The excretory duct of pyriform glands in Araneus diadematus is connected to the secretory sac through an intermediary cell ring. Apices of these cells bear thick, long microvilli and cytoplasmic extensions containing microtubules in bundles, some of which are derived from normal basal bodies. These finger-like extensions lie between the cuticular intima and the secretory product; they are thought to protect the intima and to initiate moulding of the silk thread. Structural features of the duct cells suggest that the latter play a role in the control of the water content of the silk glue which is restricted to the last portion of the duct where numerous nerve endings are inserted between cells. It is evident that duct structure and chemical and physical characteristics of silk are correlated in all spider silk glands.     

Agarose embedding affects cell wall regeneration and microtubule organization in sunflower hypocotyl protoplasts

Sunflower hypocotyl protoplasts ( Helianthus annuus L. cv. Emil) divide symmetrically to form loosely associated microcolonies when cultured in liquid medium, whereas when embedded in agarose beads they divide asymmetrically to give rise to embryo-like structures. To understand the relationship between protoplast embedding and cell division patterns, we studied the deposition of β-linked glucan and the dynamics of microtubules during early phases of culture. After one day in culture, under both culture conditions, a small proportion of the protoplasts had already begun to rebuild a β-glucan cell wall and the process reached completion in all protoplasts after 10 days. Callose deposition was faster in agarose than in liquid medium but it concerned only 30–40% of the protoplasts and was not related to either division type. No marked differences were observed in cortical arrays of microtubules. However, in embedded protoplasts perinuclear microtubules formed a well-defined basket around the nucleus; these microtubules were never observed in liquid-cultured protoplasts. A narrow preprophase band was present only in dividing protoplasts cultured in liquid medium. The results suggest that asymmetric division could be related to the lack of a narrow preprophase band and that protoplast embedding enhances nucleation or stabilization of microtubules.     

Tubulin-colchicine complex (TC) inhibits microtubule depolymerization by a capping reaction exerted preferentially at the minus end

The effects of colchicine and tubulin-colchicine complex (TC) on microtubule depolymerization were studied using the axoneme-subunit system described previously [Bergen LG, Borisy GG; J Cell Biol 84:141-150, 1980]. This system allows the independent analysis of the polymerization kinetics at both the plus and minus ends of a microtubule. Depolymerization was induced by isothermal dilution with 10 volumes of an experimental solution containing colchicine, TC, or buffer alone. Colchicine alone (5-100 microM) blocked depolymerization at the minus end, whereas depolymerization at the plus end occurred at almost control rates. A similar effect was produced by TC (0.4:1-1:1 molar ratio to free tubulin). High molar ratios of TC to tubulin (10:1) blocked depolymerization at both plus and minus ends, and intermediate molar ratios of TC:T allowed depolymerization of the plus ends but at attenuated rates. The blockage was not readily reversible; TC-affected ends neither shortened upon dilution nor grew longer upon incubation with additional tubulin. We conclude that TC at suprastoichiometric ratios to tubulin inhibits microtubule depolymerization by a capping reaction and that this effect is exerted preferentially at the minus end.     

MYC Dysregulates Mitosis,Revealing Cancer Vulnerabilities

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