PROGRESS IN PROTOZOOLOGY
PROGRESS IN PROTOZOOLOGY PROGRESS IN PROTOZOOLOGY
268 H. PLATTNER ET AL» cy topharynx V/ cytoskeletal elements (microtubules & microfi laments) MEMBRANE FUSIONS IN PARAMECIUM parasomal sacs trichocyst ghosts Mil/ coated vesicles {(&. disk-shaped vesicles smooth vesicles *Golgi apparatus ^ primary lysosomes ^ secondary lysosomes (& digesting vacuole) ^OUTPUT trichocys Ls , ' a 11/ cy toproct —\ cy toproct My osmoregulatory system (contractile vacuolo & associated elements) Fig. 1. Survey of membrane fusions in a ciliated protist (Paramecium). There are many sites of in- and output of materials which all require membrane fusions and frequently the interaction with cytoskeletal elements. Some of the sites serving material in- and output are involved in membrane recycling. (The frame in the middle gives only a rough outline of intracellular membrane interactions; for moore details see R. D. Al 1 e n, these proceedings (Part I)). Osmoregulatory systems appear to be quite independent, with regular membrane fusions at their outlet on the cell membrane Of course, one has to analyze in due time to what extent a certain model allows for conclusions of more general validity (see below). Exocytotic System in Ciliates It was noted independently by different authors using the freezefracture technique that potential exocytotic fusion sites in Tetrahymena (Satir et al. 1972, 1973, Wunderlich and Speth 1972) and Paramecium (J a n i s c h 1972, B a c h m a n n et al. 1972) display highly ordered arrays of membrane-integrated particles (MIP). Tetrahymena contains a ~ 50 nm large "rosette" of ~ 10 MIP within the cell membrane precisely at the sites where mucocysts are discharged. In Paramecium the emphasis was first on the occurrence of a~ 300 nm large double "ring" of MIP which surrounds the potential fusion site, but "rosettes" are also present right in the center of each "ring" (P 1 a 11 n e r et al. 1973, B ei sso n et al. 1976). http://rcin.org.pl
MEMBRANE FUSIONS IN PROTOZOA 269 It is difficult to derive a time sequence or — even more — any possible functional implications of static snap shots one gets from membranes by cryofixation and freeze-fracturing. This holds even more if any such attempt is done after previous chemical pretreatments (aldehyde fixation, antifreeze impregnation). In retrospect it appears, as summarized by Plattner (1981), that much of the controversies (see below) between different groups, working with protozoa, and also other groups, working with metazoan systems, came from such preparative difficulties. Both Tetrahymena and Paramecium display "rosettes" already in the resting stage, i.e., without triggering. After exocytosis triggering by a Ca 2+ -ionophore, "rosettes" are no longer present, whereas the "rings" persist and collapse (Plattner 1974). This indicates that only "rosette" but not "ring" structures are directly involved in exocytosis performance; the "rings" merely delineate the potential fusion zones without participating in the fusion process. Even stronger evidence for this comes from freeze-fracture work with mutant strains of Paramecium tetraurelia (Beisson et al. 1976). A brief survey is given in Figs. 2 and 3. Some mutations make no (tl) or grossly defective {ftA, tam 38) trichocysts which cannot be attached to the cell membrane. Other mutations (nd) allow the attachment but not the subsequent exocytotic discharge. Beisson et al. (1976) established that the discharge capacity is coupled with the presence of "rosettes". This has later been extended to further mutations (Beisson et al. 1980, Lefort-Tran et al. 1981). synthesis — packing transport attachment trigger } membrane fusion ) discharge membrane resealing membrane detachment trichless tam 8. tam 38, ftb A nd 9 (27 °C) 7S, K 401, kin 241 ( nd 6, nd 7 (all temperatures) I nd 9 {18 °C) = 'permissive' non-permissive Fig. 2. Sequence of events leading to exocytotic membrane fusion (left) and genetic dsturbances at different levels in various mutant strains of Paramecium tetraurelia. 7S is the wild type strain (K401, kin 241 are non-exocytotic mutations); for nd 9 see text. From Plattner et al. (1980) http://rcin.org.pl
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268 H. PLATTNER ET AL»<br />
cy topharynx<br />
V/<br />
cytoskeletal<br />
elements (microtubules<br />
&<br />
microfi laments)<br />
MEMBRANE FUSIONS <strong>IN</strong> PARAMECIUM<br />
parasomal<br />
sacs<br />
trichocyst<br />
ghosts<br />
Mil/<br />
coated vesicles<br />
{(&. disk-shaped vesicles<br />
smooth vesicles<br />
*Golgi apparatus ^<br />
primary lysosomes ^<br />
secondary lysosomes<br />
(& digesting vacuole)<br />
^OUTPUT<br />
trichocys<br />
Ls ,<br />
' a 11/<br />
cy toproct<br />
—\<br />
cy toproct<br />
My<br />
osmoregulatory<br />
system (contractile<br />
vacuolo & associated<br />
elements)<br />
Fig. 1. Survey of membrane fusions in a ciliated protist (Paramecium). There are<br />
many sites of in- and output of materials which all require membrane fusions<br />
and frequently the interaction with cytoskeletal elements. Some of the sites serving<br />
material in- and output are involved in membrane recycling. (The frame in<br />
the middle gives only a rough outline of intracellular membrane interactions; for<br />
moore details see R. D. Al 1 e n, these proceedings (Part I)). Osmoregulatory systems<br />
appear to be quite independent, with regular membrane fusions at their outlet on<br />
the cell membrane<br />
Of course, one has to analyze in due time to what extent a certain model<br />
allows for conclusions of more general validity (see below).<br />
Exocytotic System in Ciliates<br />
It was noted independently by different authors using the freezefracture<br />
technique that potential exocytotic fusion sites in Tetrahymena<br />
(Satir et al. 1972, 1973, Wunderlich and Speth 1972) and<br />
Paramecium (J a n i s c h 1972, B a c h m a n n et al. 1972) display highly<br />
ordered arrays of membrane-integrated particles (MIP). Tetrahymena<br />
contains a ~ 50 nm large "rosette" of ~ 10 MIP within the cell membrane<br />
precisely at the sites where mucocysts are discharged. In Paramecium<br />
the emphasis was first on the occurrence of a~ 300 nm large double<br />
"ring" of MIP which surrounds the potential fusion site, but "rosettes"<br />
are also present right in the center of each "ring" (P 1 a 11 n e r et al.<br />
1973, B ei sso n et al. 1976).<br />
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