Mutations Affecting the Trichocysts in Paramecium aurelia. I. Morphology and Description of the Mutants*

Abstract

SYNOPSIS Six types of genic mutants have been isolated. Their phenotypes range from animals with no trichocysts (trichless), to animals with morphologically abnormal trichocysts (football, stubby, pointless, screwy‐cigar), to animals which are incapable of extruding otherwise normal looking trichocysts (nondischarge). The football mutant possesses football‐shaped trichocysts, which, unlike wild‐type trichocysts, do not attach at the cortex. The stubby mutant possesses shorter trichocysts which have a very highly variable morphology. The screwy‐cigar animals have thinner and usually longer trichocysts than those found in wild‐type cells. The trichocysts of the pointless mutant have all the components of the wild‐type organelles but not in their proper relationship. Electron microscopic studies of the mutants have demonstrated that although the morphology of the various mutant trichocysts may differ, their ultrastructure and early developmental stages are comparable to those of trichocysts found in wild type. The mutations are usually pleiotropic, affecting other systems besides trichocysts. The existence of these mutants, particularly trichless, poses some interesting questions regarding the function of trichocysts, and also gives insight into the development of trichocysts.

Novel Types of Ca2+ Release Channels Participate in the Secretory Cycle of Paramecium Cells

“…Cells were counted daily, and division rates were determined by calculating the number of cell fissions per day. Capability of trichocyst exocytosis was mimicked by adding an excess of saturated picric acid (79). The pumping cycles of contractile vacuoles were determined by measuring the time between contractions of the central vacuoles of cells contained in a microdrop overlaid with paraffin oil.…”

Veratridine-Mediated Ca 2+ Dynamics and Exocytosis in Paramecium Cells

“…Wild-type cells (strain 7S), a trichocyst-free strain "trichless" (tl) [39], and a "pawn" mutant (d4-500r) devoid of ciliary voltage dependent Ca channels [20,44] but with normal secretory capacity were all grown at 25°C, the nondischarge mutant nd9 [3,4,30,40] To chelate [Ca 2+ ] o to ∼30 nM, i.e., slightly below resting levels (50-100 nM), we added 4.5 mM EGTA to the extracellular medium, as in ref. [26].…”

“…Their trichocyst contents can decondense in vitro, but since nd9-28°C cells cannot form an exocytotic fusion pore, Ca 2+ must artifically obtain access to trichocyst contents to provoke their ("internal") decondensation [40]. The tl cells form no trichocysts [39], so they display empty trichocyst docking sites [40].…”

An exocytotic mutant of Paramecium caudatum: membrane fusion without secretory contents release

“…The question then arose whether tnd 1 trichocysts contain a regular set of 'trichynins' (see Introduction and Discussion). As in P tetraurelia, these occur as a cluster of bands in SDS-PAGE the majority of which can be converted from higher apparent molecular weight (MW) to about half MW of -15-20 kDa under reducing conditions [36][37][38][39][40]49]. Figure 11 shows such typical 'trichynin' bands Oabeled by an asterisk) in trichocysts isolated from wt and tnd 1 cells.…”

“…In P. tetraurelia, elucidation of secretory mechanisms has been facilitated by the availability of many mutants, ranging from trichocyst-free strain tl [39] to nondischarge (nd) strains which cannot perform exocytotic membrane fusion though their trichocysts are docked at the cell membrane [40][41][42][43][44], just as in wildtype (wt) cells [11]. Some nd-mutants, tndl and tnd2, have also been described in P. caudatum [45,46].…”