ULTIMATE COMPUTING - Quantum Consciousness Studies

Models of Cytoskeletal Computing 171
8.2.10 Dynamic MT Probing/Kirschner and Mitchison
Figure 8.5: Robert Jarosch has proposed that actin filaments wind around
microtubules and contract, causing MT to rotate and oscillate around their long
axis. With permission from Robert Jarosch (1986).
Strong evidence supports the concept of dynamic instability in microtubule
assembly (Chapter 5). Many MT exist in either growing or shrinking phases and
MT stabilized at merely one end by centriole based microtubule organizing
centers (MTOC) tend to predominate. Selective retention of MTOC based MT
establishes cell polarity important in extension of axons and dendrites, elongation
of cells in embryological development, and formation of lamellipodia and
filopodia in locomotory cells. All are examples of the “Indian rope trick” in which
cells somehow choose their direction of growth, and then grow in that direction.
A cue presented at the cell periphery can lead to rearrangements of cell symmetry
and polarity. Kirschner and Mitchison (1986) ask: “how can a peripheral clue lead
to reorganization deep within a cell” One possibility is that a signal is relayed to
the microtubule organizing center leading to a change in its structure, orientation,
and directed nucleation of microtubules. This would be consistent with a primary
role for information integration and decision making within the MTOC. A simpler
“non-hierarchical” idea is that a signal at the periphery affects distribution
directly. Since the whole cytoskeletal array is very dynamic, it would only be