Initiation and growth of microtubules from mitotic centers in lysed mammalian cells.

Metaphase PtK1 cells, lysed into polymerization-competent microtubule protein, maintain a spindle which will gain or lose birefringence depending on the concentration of disassembled tubulin subunits used in the lysis medium. Concentrations of tubulin subunits greater than the equilibrium monomer value promote a rate and extent of birefringence increase that is proportional to the subunit concentration. Increase in spindle birefringence can be correlated with an increase in tubule number, though the relationship is not strictly linear. Increase in spindle tubule number is due to an vivo-like initiation of tubules at the mitotic centers, as well as tubulin addition onto pre-existing spindle fragments. Colcemid-treated prometaphase cells lysed into polymerization-competent tubulin develop large asters in the region of the centrioles and short tubules at kinetochores, making it unlikely that all microtubule formation in lysed cell preparations is dependent on tubulin addition to short tubule fragments. Asters can also form in colcemid-treated prometaphase cells lysed in tubulin that is incapable of spontaneous tubule initiation, suggesting that the centriolar region serves a tubule-initiator function in our lysed cell preparations. The ability of the centriole to initiate microtubule assembly is a time-dependent process-a ripening effect takes place between prophase and late prometaphase. Ripening is expressed by an increase in the number and length of tubules found associated with the centriolar region.

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Identification and characterization of microtubule proteins from myxamoebae of Physarum polycephalum

Biochemical Journal ◽

10.1042/bj1890305 ◽

1980 ◽

Vol 189 (2) ◽

pp. 305-312 ◽

Cited By ~ 13

Author(s):

A Roobol ◽

C I Pogson ◽

K Gull

Keyword(s):

Physarum Polycephalum ◽

Microtubule Assembly ◽

Alpha Tubulin ◽

Microtubule Associated Proteins ◽

Cell Extracts ◽

Microtubule Protein ◽

Associated Proteins ◽

Microtubule Formation

Cell extracts of myxamoebae of Physarum polycephalum have been prepared in such a way that they do not inhibit assembly of brain microtubule protein in vitro even at high extract-protein concentration. Co-polymers of these extracts and brain tubulin have been purified to constant stoichiometry and amoebal components identified by radiolabelling. Amoebal tubulin has been identified as having an alpha-subunit, mol.wt. 54 000, which co-migrates with brain alpha-tubulin and a beta-subunit, mol.wt. 50 000, which co-migrates with Tetrahymena ciliary beta-tubulin. Non-tubulin amoebal proteins that co-purify with tubulin during co-polymer formation have been shown to be essential for microtubule formation in the absence of glycerol and appear to be rather more effective than brain microtubule-associated proteins in stimulating assembly. The mitotic inhibitor griseofulvin (7-chloro-2′,4,6-trimethoxy-6′-methylspiro[benzofuran-2(3H),1′-cyclohex-2′-ene] −3,4′-dione), which binds to brain microtubule-associated proteins and inhibits brain microtubule assembly in vitro, affected co-polymer microtubule protein in a similar way, but to a slightly greater extent.

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Application of GPS in Combination with Repeated Gravimetry for Monitoring Time-Dependent Process

10.3997/2214-4609-pdb.324.629 ◽

1993 ◽

Author(s):

E. Grotem

Keyword(s):

Time Dependent ◽

Time Dependent Process ◽

Monitoring Time ◽

Dependent Process

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Sleep is for rest, waking consciousness is for learning and memory – of any kind

Behavioral and Brain Sciences ◽

10.1017/s0140525x05440029 ◽

2005 ◽

Vol 28 (1) ◽

pp. 86-87 ◽

Cited By ~ 3

Author(s):

Robert P. Vertes

Keyword(s):

Learning And Memory ◽

Time Dependent ◽

Slow Time ◽

Substantial Evidence ◽

Unique Role ◽

Memory Processing ◽

Time Dependent Process ◽

Dependent Process ◽

Procedural Tasks ◽

Task Acquisition

Although considerable attention has been paid to the possible involvement of sleep in memory processing, there is no substantial evidence for it. Walker describes a phenomenon of consolidation-based enhancement (CBE), whereby performance on select procedural tasks improves with overnight sleep; that is, without additional practice on the tasks. CBE, however, appears restricted to a few tasks, and even with these tasks CBE is not confined to sleep but also occurs during wakefulness. Sleep serves no unique role in this process. At best, CBE is a slow, time-dependent process of consolidation that begins with task acquisition in waking and can under some circumstances extend to sleep.

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