Biology Reference
In-Depth Information
hitherto hypothetical aspect to be scrutinized. As in other exocytotic pro-
cesses ( Pang and S¨dhof, 2010 ), any of these channels may provide Ca 2 þ
for the extrusion of vacuole contents at the pore.
The remarkable input of data from Tetrahymena is in part due to expres-
sion as GFP-fusion proteins which otherwise would have remained
undetected. Therefore, these components may be assumed to have a broader
distribution among CVCs, also in other species. This may also be the case
with SNAREs, CRCs, and Stomatins which so far have been identified
and localized to the pore only in Paramecium .
6.2. Biogenesis and epigenetically determined positioning
of CVC in Paramecium
New CVCs are formed anterior to each of the two CVC before cells
undergo cytokinesis, their positioning being under epigenetic control in
Tetrahymena ( Frankel, 2000; Nanney, 1966 ) and Paramecium ( Beisson,
2008; Klotz et al., 2003 ). It appeared to us most attractive to study the rel-
evance of specific CVC proteins for biogenesis by inducing de novo forma-
tion. We tried the method elaborated by Iwamoto et al. (2003) to induce
formation of supernumerary CVCs in sterile P. multimicronucleatum by expo-
sure to a hypertonic medium with increased [Ca 2 þ ] o . Unfortunately, this
method—although well reproducible under the same culture
conditions—proved unsuccessful with P. tetraurelia cultures which were
raised for gene silencing by feeding with transformed bacteria. These con-
tained specific nucleotide sequences encoding SNAREs ( Sch¨nemann et al.,
2013 ) and other CVC components to be silenced, with the aim to study the
relevance of specific components for biogenesis. For these practical reasons,
we have been restricted to register occasional effects on organelle biogenesis
under asynchronous conditions ( Table 9.3 ).
Silencing of different membrane components in Paramecium cultures rev-
ealed that the organelle-resident v- and t-SNAREs are important to a dif-
ferent extent ( Sch¨nemann et al., 2013 ). Silencing of some of them makes
the system particularly sensitive to increased [Ca 2 þ ] in the medium. The
organelle was also impaired after silencing the IP 3 R or of some SUs of
the organelle-resident H þ -ATPase ( Sch ¨ nemann et al., 2013 ). This might
be due to a remote effect as silencing of the IP 3 R also affects other functions;
this is concluded from the substantial reduction of the biogenesis of secretory
organelles (trichocysts) ( Ladenburger et al., 2006 ). For unknown reasons,
expression of a a2a3 chimera of the H þ -ATPase can cause swelling of the
CVC or formation of supernumerary organelles ( Wassmer et al., 2006 ).
Search WWH ::




Custom Search