Contractile Vacuole Complex—Its Expanding Protein Inventory - International Review of Cell and Molecular Biology - page 387

5. CYTOSKELETAL ELEMENTS, MOTOR PROTEINS,
ENDOCYTOTIC INPUT, AND CLATHRIN

Microtubules are dominant components of the CVC, whereas the
presence of actin is generally denied. This may be premature, as we shall dis-
cuss. Also under debate is the role of membrane input by endocytosis and
participation of clathrin.

5.1. Cytoskeletal components and motor proteins
Microtubules accompany the CVC from the pore to the end of radial canals
in Paramecium ( Allen, 2000; Schneider, 1960 ) as well as in Tetrahymena
( Frankel, 2000 ). In ciliates, the microtubule cytoskeleton of the CVC shapes
the organelle and its substructures. Their recognition by monoclonal anti-
bodies depends on the respective posttranslational modification ( Adoutte
et al., 1991 ) and only some of the commercial antibody types are successful
( Wassmer et al., 2006 ). In Dictyostelium , CVC-associated microtubules are
much less evident. Here, no CVC staining is seen with antibodies recogniz-
ing the mitotic apparatus ( Gabriel et al., 1999 ), but again a specific commer-
cial monoclonal antibody clearly reveals a microtubular system of the CVC
( Jung et al., 2009 ).
At the pore, g -tubulin is found in Tetrahymena ( Shang et al., 2002 ) and
Paramecium ( Klotz et al., 2003 ); it thus can serve for microtubule nucleation.
More specifically, in Tetrahymena, the pore is also reported to contain
glutamylated tubulin, that is, not only GLU- g -tubulin ( Shang et al.,
2002 ) but also GLU- a -tubulin ( Wloga et al., 2008 ). The relevance of this
modification for CVC biogenesis and function remains to be settled.
In Tetrahymena , tubulin along radial arms is acetylated ( Gaertig et al., 1995 )
as it is in Paramecium ( Callen et al., 1994 ). In Paramecium , microtubules
accompanying the CVC in full length also contain glutamylated tubulin
( Br ´ et al., 1994 ). This microtubular scaffold of the CVC mediates its char-
acteristic star-like shape in ciliates. It is unsettled whether in Paramecium such
modifications mediate insensitivity of the CVC to nocodazole ( Tani et al.,
2000 ), although this is a most efficient drug in these cells ( Pape et al.,
1991 ). The plus minus-directed motor, dynein, is associated with the

CVC microtubule system in Paramecium ( Fok et al., 2008 ). There may be
additional motor proteins at work to exert a pulling force to the radial arms
also in opposite directions, as known from the endoplasmic reticulum.

!