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to the cell membrane over a relatively large area, with a very narrow cyto-
plasmic seam in between (
Allen, 2000
). Some chemically still undefined
material is seen in between (
McKanna, 1973
). As mentioned, microtubules
emanate from the pore and extend to the tip of radial arms, whereas alveolar
sacs are approaching only at a distance.
In
Dictyostelium
, the exocytotic process depends on Rab8 (
Essid et al.,
2012
) and on
Dd
secA (
Essid et al., 2012; Sriskanthadevan et al., 2009
), a
homolog of Munc18 which in mammalian cells interacts with SNAREs
(
Meijer et al., 2012; Zilly et al., 2006
). By implication, SNAREs will par-
ticipate as will exocyst proteins—a postulate derived from work with
Chlamydomonas
(
Komsic-Buchmann et al., 2012
). These components can
be assumed to form part of the kiss-and-run fusion/fission machinery at
the pore. From CV docking until discharge, a sequential attachment and
detachment of a variety of additional proteins has been proposed, including
Disgorgin, Drainin, and LvsA (
Essid et al., 2012
). MyoJ (a type V myosin) is
also mandatory for CV docking in
Dictyostelium
(
Jung et al., 2009
).
In ciliates, a variety of components have been localized to the pore, yet all
only at the LM level (
Table 9.1
). In
Tetrahymena
, these include adaptor pro-
tein AP-2 (
Elde et al., 2005
), calmodulin (
Numata and Gonda, 2001; Suzuki
et al., 1982
), centrin4 (
Stemm-Wolf et al., 2005
), a NIMA (never in mitosis
A) kinase-related protein kinase (
Wloga et al., 2006
),
g
-tubulin (
Shang et al.,
2002
), and acetylated tubulin (
Gaertig et al., 1995
). Remarkably, in mam-
malian neurons, NIMA family kinases are relevant for microtubule organi-
zation (
Chang et al., 2009
).
In
Paramecium
, pore-associated proteins include calmodulin (
Fok et al.,
2008
), the SNARE-chaperone NSF (
Kissmehl et al., 2002
), SNAREs type
Syb2 (
Schilde et al., 2006
), Syx2 (
Kissmehl et al., 2007
), Syb9, and Syx15
(
Sch¨nemann et al., 2013
); the latter two, however, also occur over the rest
of the CVC (except the decorated spongiome;
Sch¨nemann et al., 2013
). In
addition, CRCs types
Pt
CRC-VI-2 and
Pt
CRC-VI-3 are observed here
(
Ladenburger and Plattner, 2011
); however,
Pt
CRC-VI-2 is also present
on ill-defined cortical vesicles outside the CVC and
Pt
CRC-VI-3 at the
terminal cisternae (considered as early endosomes;
Allen et al., 1992
).
Stomatins of type 1 and 4 are also localized to the CVC pore in
Paramecium
(
Reuter et al., 2013
). This is interesting as Stomatin is the only member of
the stomatin-prohibitin-flotillin/reggie-HflC/K family currently known
from protozoa and since Stomatin is associated predominantly, if not exclu-
sively, with mechanosensitive Ca
2
þ
-influx channels (
Lapatsina et al., 2012
).
Therefore, the pore may have a sensor for the filling state of the CV—a
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