Microtubule-independent

Goncyy No. If this were the case, you would expect the side of the embryo to assume posterior character in the rare cases where sperm entry is lateral. Goldstein Hird (1996) showed this not to be the case. Instead, what they observed is that the male pronucleus and associated centrosomes move along the cell cortex towards the nearest pole, which then becomes the posterior of the embryo. This movement does not require cytoplasmic dynein function (P. Gonczy, unpublished observations) and may also be microtubule-independent. 

Summary Microtubule-Independent Control of Microfibril Orientation... 

P.A. Conrad, E.J. Uittenbogaard, Y. S. Ying, R.G.W. Anderson, and G.S. Bloom, Caveolin cycles between plasma membrane caveolae and the Golgi complex by microtubule-dependent and microtubule-independent steps, J. CeU. Biol., 1995, 131, 1421-1433. 

Centrins are calmodulin-like proteins that have an important function in the organization and duplication of microtubules. Like CaM, centrin is also comprized of two structurally independent globular domains connected by a flexible tether, and each domain is... 

Thus far, microtubules and actin filaments and their associated proteins have been discussed to advantage as independent cytoskeletal components. In actual fact, all of the components of the cytoskeleton (including intermediate filaments) are precisely integrated with one another (Langford, 1995), as well as with various cytoplasmic organelles, the nuclear membrane, the plasma membrane, and the extracellular matrix. In its totality the cytoskeleton subserves many coordinated and regulated functions in the cell ... 

Kalab P, Kubiak JZ, Verlhac MH, Colledge WH, Maro B 1996 Activation of p90Kk during meiotic maturation and first mitosis in mouse oocytes and eggs MAP kinase-independent and dependent activation. Development 122 1957—1964 Kubiak JZ, Weber M, dePennart H, Winston N, Maro B 1993 The metaphase II arrest in mouse oocytes is controlled through microtubule-dependent destruction of cyclin B in the presence of CSF. EMBO J 12 3773-3778... 

It would be interesting to learn whether 4,5-dihydro-5 a-hydroxy-4 a-methoxy-6a,12a-dehydro-a-toxicarol interferes with the enzymatic activity of topoisomerase. Note that taxol, a successful chemotherapeutic agent that hampers the normal microtubule machinery, has been suggested to involve additional cytotoxic pathways including p53-independent apoptosis of tumor cells and inhibition of topoisomerase II (42). 

Donato R. 1988. Calcium-independent, pH-regulated effects of S-100 proteins on assembly-disassembly of brain microtubule protein in vitro. J Biol Chem 263(1) 106—110. 

Walker, R., Pryer, N., and Salmon, E. (1991). Dilution of individual microtubules observed in real time in vitro Evidence that cap size is small and independent of elongation rate./. Cell Biol. 114, 73-81. 

We conclude that dynamic instability is a means of creating an endless stream of cell types with only one common structure and with the choice of a few anchoring molecules. But this is possible only because there is no necessary relationship between the common structure of the cytoskeleton and the cellular structures that the cytoskeleton is working on. The anchoring molecules (or accessory proteins) are true adaptors that perform two independent recognition processes microtubules on one side and different cellular structures on the other side. The resulting correspondence is based therefore on arbitrary rules, on true natural conventions that we can refer to as the cytoskeleton codes. 

Cash AD, Aliev G, Siedltik SL, Nunomura A, Fujioka H, Zhu X, Raina AK, Vinters HV, Tabaton M, Johnson AB, Paula-Barbosa M, Avila J, Jones PK, Castellani RJ, Smith MA, Perry G (2003) Microtubule reduction in Alzheimer s disease and aging is independent of tau filament formation. Am J Pathol 162 1623-1627... 

Kinesins are motor proteins that move along microtubules. We have seen that myosin moves along actin filaments by a process in which actin is released in each cycle a myosin head group acting independently dissociates from actin after every power stroke. In contrast, when a kinesin molecule moves along a microtubule, the two head groups of the kinesin molecule operate in tandem — one binds, and then the next one does. A kinesin molecule may take many steps before... 

Kinesin hydrolyzes ATP at a rate of approximately 80 molecules per second. Thus, given the step size of 80 A per molecule of ATP, kinesin moves along a microtubule at a speed of 6400 A per second. This rate is considerably slower than the maximum rate for myosin, which moves relative to actin at 80,000 A per second. Recall, however, that myosin movement depends on the independent action of hundreds of different head domains working along the same actin filament, whereas the movement of kinesin is driven by the processive action of kinesin head groups working in pairs. Muscle myosin evolved to maximize the speed of the motion, whereas kinesin functions to achieve steady, but slower, transport in one direction along a filament. 

Kidder, G. M., Rains, J. and McKeon J. (1987). Gap junction assembly in the preimplantation mouse conceptus is independent of microtubules, microfilaments, cell flattening and cytokines. Proc. Natl. Acad. Sci. USA 84, 3718-3722. 

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