Cellular dynamics of conjugation in the ciliate euplotes aediculatus. I. Cytoskeletal elements

Abstract

The fate and possible roles of the cytoskeleton in the process of conjugation in the hyptrich ciliate Euplotes aediculatus were investigated. Following the coalescence of the plasma membranes of the conjugant cells, a fusion zone or bridge of cytoplasm contributed by both partners is constructed. The sub-alveolar microtubule layers of the vegetative cell cortex remain in place to define the fusion zone boundaries after cell union. The initial fusion zone consists primarily of featureless ground cytoplasm; soon the ground plasm becomes crowded with microtubules and anastomosing smooth endoplasmic reticulum, which become displaced only late in conjugation as the migratory pronuclei are exchanged between partners. Fusion zone microtubules, functioning in some undetermined way, may be involved in the nuclear migration. Resorption of the posterior portion of each partner's buccal apparatus results in the degradation of the component cilia within acid phosphatase-positive autophagic bodies. Silver staining for light microscopy shows that the late fusion zone contracts forward from the posterior border, then constricts to separate the conjugants. In some separating pairs remnants of a microfilamentous assembly are seen at the posterior edge of the fusion zone; the full extent of this system may be masked by partial degradation due to osmium tetroxide fixation. Treatment of conjugants for 6 hours with cytochalasin B prevents separation, possibly through inhibition of the actin-like microfilament assembly in the fusion zone. The observations and experiments favor a model of cell separation following conjugation in which the fusion zone is resorbed by motile or contractile processes occurring within or around the fusion bridge itself.

Identification and Properties of Plateins, Major Proteins in the Cortical Alveolar Plates of Euplotes1

“…Euplotes offers a number of advantages as a model cell type to improve understanding of morphogenic mechanisms. We have published [12,131 results of an investigation about this phenomenon, and have proposed a model concerning some aspects ofnew cell surface assembly. This model is based primarily on ultrastructural evidence, and requires further data that could be provided by application of molecular probes specific for selected cortical components.…”

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

“…Considering that our observations on mating behavior and morphogenesis have been repeated for two different species, it seems reasonable to regard the phenomena reported in the present paper as general for the species of the genus Aspidisca. Although the general conjugation pattern is very similar to that reported for different species of the genus Euplotes, the most widely studied Hypotrichida as regards conjugation (Diller 1975;Kloetzel 1975;Geyer and Kloetzel 1987a), singular characteristics have been found.…”

“…Interestingly, beside their behavior, the contribution of the two partners to the "tube" formation also differs: the majority of both the pellicle and the cytoplasm are supplied by the rotating mate (B). The presence, within the FZ cytoplasm of microtubules, whose function may be to provide the structural stability and the maintenance of the FZ bridge as a discrete entity, has been reported in E. aediculatus (see Geyer and Kloetzel 1987a). 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.…”

Structure and Protein Composition of a Basal‐Body Scaffold (“Cage”) in the Hypotrich Ciliate Euplotes

“…This ciliate has been widely used in studies of cytoskeletal morphogenesis (Fleury ,b; Fleury et al. ; Foissner ; Geyer and Kloetzel ; Ruffolo ; Wise ), and some of the proteins making up structural elements of its cortex have been described (Kloetzel ; Kloetzel et al. ,b; Williams ; Williams et al.…”

“…The present study was undertaken in an effort to better understand the structural basis for kinetosome clustering in the hypotrich Euplotes. This ciliate has been widely used in studies of cytoskeletal morphogenesis (Fleury 1991a,b;Fleury et al 1998;Foissner 1978;Geyer and Kloetzel 1987;Ruffolo 1976;Wise 1965), and some of the proteins making up structural elements of its cortex have been described (Kloetzel 1991;Kloetzel et al 2003a,b;Williams 1991;Williams et al 1989). The results presented here characterize more fully the structure of another key element of the Euplotes cortex, the scaffold or cage units common to polykinetids, both cirri and membranelles.…”