Nuclear and Cortical Regulation in Doublets of Paramecium: II. When and How do Two Cortical Domains Reorganize to One?

Abstract

Homopolar doublets with twofold rotational symmetry were generated in Paramecium tetraurelia and in P. undecaurelia by electrofusion or by arrested conjugation. These doublets underwent a complex cortical reorganization over time, which led to their reversion to singlets. This reorganization involved a reduction in number of ciliary rows, a progressive inactivation and loss of one oral meridian, and a reduction and eventual disappearance of one cortical surface (semicell) situated between the two oral meridians. The intermediate steps of this reorganization included some processes that resemble those previously described in regulating doublets of other ciliates, and others that are peculiar to members of the "P. aurelia" species-group and some of its close relatives. The former included a disappearance of one cortical landmark (a contractile vacuole meridian) and transient appearance of another (a third cytoproct) within the narrower semicell. The latter included a reorganization of the paratene zone and the associated invariant (non-duplicating) region to occupy the entire narrower semicell and a redistribution of zones of most active basal-body proliferation within the opposite, wider semicell. The final steps of reorganization involved anterior displacement, invagination, and resorption of one of the two oral apparatuses and eventual disappearance of the associated oral meridian. An oral meridian deprived of its oral apparatus, either by spontaneous resorption or microsurgical removal, could persist for some time in "incomplete doublets" before regulating to the singlet condition. The phylogenetically widespread events encountered in the regulation of doublets to singlets suggest that Paramecium shares some of the global regulatory properties that are likely to be ancestral in ciliates. The more specific events are probably associated with the complex cytoskeletal architecture of this organism and with the frequent occurrence of autogamy that was described in the preceding study (Prajer et al. 1999).

Genetic and Epigenetic Factors Affecting Meiosis Induction in Eukaryotes Revealed in Paramecium Research

“…2) (FAURÉ-FREMIET 1948;SONNEBORN 1963;KACZANOWSKA & DUBIELECKA 1983). The correlations between cortex and organelles in doublet cells during the regulation process were extensively examined by and IFTODE et al (2001). The changes of the main cortical and nuclear structures which can be observed in regulating populations are schematically presented in Fig.…”

“…In consequence, this leads to the gross asymmetries in the distribution of the macronuclear DNA to the two daughter doublets (BERGER & MORTON 1980). The homopolar doublets underwent a complex cortical reorganization over the time of regulation (for details see IFTODE et al 2001). The important event in this process is the increasing dominance of one oral region and final invagination and resorption of the other one (Figs 8 & 9), preceding the reversion to the singlet state.…”

Glucose, Sorbitol and Insulin as Exogenous Agents that Monitor the Interautogamous Interval (IAI) in Paramecium primaurelia

“…Paramecium, an eukaryotic, unicellular organism, with its whole genome sequenced (SPERLING et al 2002;ZAGULSKI et al 2004) and a genome database in the -process of creation, is an excellent model species for the study of mechanisms regulating the processes of development and morphogenesis on both physiological and genetic levels (IFTODE et al1989(IFTODE et al , 2001JERKA-DZIADOSZ et al 1992;KACZANOWSKA et al 1996;KRZYWICKA et al 2001;PRAJER et al 1997RUIZ et al 2000). It is also exemplary for the elucidation of factors affecting growth and clonal life (HAGA 1991;KOOECIUSZKO & PRAJER 1989MIWA 1984;PRAJER 1994;PRAJER & KOOECIUSZKO 1994).…”