Biology Reference
In-Depth Information
Fig. 21.5 Model of actin
expansion driving MTOC
polarization. a Actin first
accumulates at the synapse in
a small patch in the area of
the future cSMAC.
Microtubules may be linked
to actin through IQGAP or
CIP4. b During maturation of
the synapse, actin is cleared
from the cSMAC area and
widens out in the form of a
ring. Microtubules anchored
to actin would be put under
tension, drawing the MTOC
up to the synapse
21.3 Alternative Mechanisms for MTOC Translocation
Although there are a number of lines of evidence that dynein anchored at the
synapse is responsible for MTOC translocation, alternative or supplemental
mechanisms have been proposed. Several studies have implicated an actin or
actomyosin-based movement. One proposed mechanism is based on observations
that actin is initially polymerized in the region of the cSMAC but it is then cleared
out of the cSMAC as the patch of actin takes the form of an expanding ring
(Stinchcombe et al.
2006
). A similar observation is seen in the studies by Bunnel
and colleagues who followed actin polymerization at the surface where Jurkat cells
contact anti-TcR-coated coverslips. They saw that actin polymerization begins in
the center of the contact zone and then widens out as an expanding ring (Bunnell
et al.
2001
). One could envision that if microtubule plus ends were tied to actin,
then tension would develop on microtubules as the ring expanded (Fig.
21.5
).
