Contractile Vacuole Complex—Its Expanding Protein Inventory - International Review of Cell and Molecular Biology - page 385

(FCH-Bin-amphiphysin-Rvs) protein, is known from the CVC of
Dictyostelium ( Heath and Insall, 2008 ; see Section 4.2 ). Generally, BAR pro-
teins serve for the formation of tubular extensions from planar membranes
( Mim and Unger, 2012; Wu et al., 2010 ). Since these proteins are not
known to cause tubule branching, as occurring in the CVC, possible mech-
anisms are discussed in Section 7 . Prerequisite to all this transformation are
mechanosensitive Ca 2 þ channels of the type described in Section 3.2 , as they
are required for sensing the pressure in the CV and for initiating contents
release and organelle collapse. They may also generate a Ca 2 þ signal for
membrane restructuring. All this remains to be analyzed in detail.
SNAREs may also be involved, for example, as trans-complexes, in
keeping spongiome tubules in dense packing independent of fusion pro-
cesses. They may also initiate reversible fusion processes within the
spongiome as occurring between the smooth and the decorated spongiome
under hyperosmotic conditions ( Ishida et al., 1996 ). Thus, de-/
reconnection of parts of the spongiome might be a regulation principle in
response to changing physiological requirements.
4.2. CVC components known specifically from Dictyostelium
At this point, we recognize that many more molecular details are known
from Dictyostelium (which is not true of all aspects).
4.2.1 Dajumin and MEGAPs
Dajumin has been defined as a standard marker for the CV in Dictyostelium
( Gabriel et al., 1999 ) as it does not dissociate from the CV membrane
( Du et al., 2008 ), in contrast to some of the proteins listed in Table 9.2 .
Its function remains to be established, and it looks as if no similar protein
has been reported from other systems. In Dictyostelium , proteins of the
MEGAP (mental retardation GTPase-activating protein) group, type
F-BAR, associate with the forming tubules of the CVC whose formation
they drive ( Heath and Insall, 2008 ). Their inactivation in Dictyostelium delays
pumping activity of the CV. For more details, see Section 4.1 .
4.2.2 Cell adhesion molecule and Rh50 protein
The Dictyostelium CV is reported to contain a Ca 2 þ -sensitive cell-adhesion
molelcule, Dd DAD-1 ( Sriskanthadevan et al., 2009 ). This molecule is syn-
thesized on free ribosomes and transported to the CV for insertion into the
plasma membrane. There it may be transported by previous release in