Cellular dynamics of conjugation in the ciliate euplotes aediculatus. II. Cellular membranes

Abstract

The formation and subsequent dissolution of a common bridge of cytoplasm between conjugating ciliated protozoan cells provides an excellent opportunity to follow the dynamics of the cellular membrane systems involved in this process. In particular, separation of conjugant partners offers the chance to observe, at a fixed site on the cell surface, how the ciliate surface complex of plasma and alveolar membranes (collectively termed the "pellicle") is constructed. Consequently, cortical and cellular membranes of Euplotes aediculatus were studied by light and electron microscopy through the conjugation sequence. A conjugant fusion zone of shared cytoplasm elaborates between the partner cells within their respective oral fields (peristomes) to include microtubules, cytosol, and a concentrated endoplasmic reticulum (heavily stained by osmium impregnation techniques) that may also be continuous with cortical ER of each cell. Cortical membranes displacd by fusion are autolyzed in acid phosphatase-positive lysosomes in the fusion zone. As conjugants separate, expansion of the plasma membrane may occur through the fusion of vesicles with the plasma membrane, presumably at bare membrane, presumably at bare membrane patches near the fusion zone. The underlying cortical alveolar membranes and their plate-like contents are reconstructed beneath the plasma membrane, apparently by multiple fusions of dense-cored alveolar precursor vesicles (APVs). These precursor vesicles themselves appear to condense directly from the smooth ER present in the fusion zone. No Golgi apparatus was visible in the fusion zone cytoplasm, and no step of APV maturation that might involve the Golgi complex was noted.

Green fluorescent protein‐tagged sarco(endo)plasmic reticulum Ca2+‐ATPase overexpression in Paramecium cells: isoforms, subcellular localization, biogenesis of cortical calcium stores and functional aspects

“…In the ciliate Euplotes , EM morphological studies indicate that ASs after conjugation are reformed by fusion of some smooth tubules and vesicles whose structure is different from regular ER (Geyer and Kloetzel, 1987). This is compatible with our Fig.…”

Mating by conjugation in two species of the genus Aspidisca (Ciliata, Hypotrichida): an electron microscopic study

“…19) is in favor of this hypothesis. A similar process has been reported for the reconstruction of the cortex in the FZ regions of Euplotes aediculatus (Pierson, 1943) conjugants near separation (Geyer and Kloetzel 1987b). It has been suggested that new alveoli form by the fusion of numerous specialized membranous vesicles termed "alveolar precursor vesicles" (APVs).…”

“…At the end of the rotation process in a pair of Aspidisca species, the FZ is a structure in some way external to the cell body: probably for this reason the microtubular network becomes denser at the periphery of the FZ forming subcortical support. Sheets of basal microtubules as described in Euplotes vannus (Muller 1786) and E. aediculatus (see Nobili 1967;Geyer and Kloetzel 1987b) have not been observed. The involvement of the dorsal surface of the non-rotating partner (A), restricted only to the dorsal side of the FZ, is clearly evidenced by the presence of the 70 nm bodies outside the cell membrane.…”

Plateins: A Novel Family of Signal Peptide‐Containing Articulins in Euplotid Ciliates1

“…Ciliates typically possess a monolayer of flattened membranous cisternae (termed ‘cortical alveoli’), tightly abutted to one another, just beneath the plasma membrane. Euplotids differ from most ciliates in that they construct one of the main cytoskeletal elements of their cortexes within the cortical alveoli in the form of rigid ( intra ) alveolar plates (AP; see Geyer and Kloetzel 1987; Hausmann and Hiilsmann 1996; Hausmann and Kaiser 1979). This assemblage of alveolus‐AP units is integrated into a contiguous mosaic surface (Fig.…”