Patterned Arrays of Intramembranous Particles in the Bristle Cilia of Three Different Species of Euplotes1

Freeze-fractured cells of three marine species of Euplctes (E. crassus, E. raikovi, and E. rariseta) show bristle cilia with patterned arrays of intramembranous particles. Such arrays are essentially of three types, in different positions along the bristle shaft. One array is located near the bristle base and shows a plate-like shape. It appears in a close spatial correspondence with the lasiosome network, which is a structure consisting of interconnected electron-dense bodies lying in between the peripheral axonemal doublets and the bristle membrane. The second type of array, apparently typical of only E. raikovi, consists of eight to ten longitudinal rows of particles that occupy most of the intermediate portion of the bristle. The third type of array appears differently shaped in different species and occurs at the bristle apex.     

Competition Among Homologous Polypeptide Pheromones of the Ciliate Euplotes raikovi for Binding to Each Other's Cell Receptors

ABSTRACT. Purified preparations of the polypeptide pheromones Er-1 and Er-2 were obtained from type I and II cells of Euplotes raikovi , respectively, radiolabeled, and used to study their ability to compete with each other in binding to the same type I and II cells and to type × cells secreting Er-10, another pheromone homologous to Er-1 and Er-2. It was shown that: 1) These radiolabeled pheromone preparations bind, with similar but not identical affinities, to cells from which they originate as well as to cells of the other types. 2) Every pheromone binding reaction can be completely inhibited by another homologous pheromone added in excess to cells. These results are discussed in relation to phenomena, common in ciliates, of instability of (homotypic) mating pairs formed between genotypically identical cells suspended with a foreign (nonself) pheromone.     

Relationships between Cell Cycle and Conjugation in 3 Hypotrichs*

SYNOPSIS. Relationships between the cell cycle and the beginning of conjugation were analyzed for 3 hypotrichs: Diophrys scutum, Oxytricha bifaria, and Euplotes crassus. The first 2 species enter conjugation with micronuclei in G₁; the latter species with a micronucleus in G₂. The 1st micronuclear division of conjugating E. crassus is mitotic. Thus meiotic DNA replication occurs when the cells of each species have already entered the mating process. Cells from asynchronous populations start conjugation with their macronuclei primarily in G₁ or more rarely at the beginning of the S stage in a percentage significantly different from that expected on the basis of random mating among all cells in the population. Also, macronuclear replication, when already begun, was blocked in cells undergoing conjugation. Therefore only the G₁ or the very early S stages of the cell cycle are compatible with conjugation in the 3 analyzed species.     

Multiconjugant Complexes of Euplotes Crassus: an Instance of Coordination of Nuclear Events*,†

SYNOPSIS In the ciliate Euplotes crussus, doublet cells of 3 complementary mating types were mixed and multiconjugant complexes obtained. The cells were not uniform in the G, stage at the time of mixing. Despite asynchrony, the nuclear events of conjugation started and progressed coordinately in all the members of each complex, leading to a synchronous exchange of pronuclei. An adjustment of the cellular timing takes place before the nuclei of multiconjugants begin dividing. This adjustment probably occurs through specific ciliary contact during preconjugant interaction.     

Identification of the Tubulin Gene Family and Sequence Determination of One β-Tubulin Gene in a Cold-Poikilotherm Protozoan, the Antarctic Ciliate Euplotes focardii

ABSTRACT. Four different tubulin genes were identified in the somatic nucleus (macronucleus) of Euplotes focardii , a strictly coldadapted, Antarctic ciliate: one of 1,800 bp for α-tubulin and three of 2,150, 1,900, and 1,600 bp, respectively, for β -tubulin. Preliminarily analysed for restriction fragment length polymorphisms, these genes showed remarkable differences in organisation from tubulin genes of other ciliates which live in temperate areas and were analysed in parallel with E. focardii. The complete coding sequence of the 1,600 bp β -tubulin gene was then determined and shown to contain unique structural features of potential importance for E. focardii microtubule organization and activity. Of eight unique substitutions detected, seven were concentrated in the large amino terminal domain of the molecule that directly interacts with the carboxy terminal region of α-tubulin for heterodimer formation. Sequence analysis of the cloned gene revealed, in addition, a potential new exception in the use of the genetic code by ciliates. A TAG codon was aligned in correspondence with Trp-21 which is strictly conserved in every tubulin sequence so far determined.     

Life Cycle of Autogamous Strains of Euplotes minuta*

SYNOPSIS. The life cycles of 5 autogamous strains of Euplotes minuta are reported. Interautogamic intervals (measured as number of fissions) are quite variable among clones belonging to the same strain, while their variability is much reduced (15 fissions) among sublines of the same clone. By selecting the clone with the shortest immature period to start successive autogamous generations, it has been found that all clones undergo autogamy almost synchronously and have a very short period of immaturity at the 5th autogamous generation. Both conjugation and autogamy, however, are consistently followed by immature periods in all autogamous strains examined. Mating capacity as well as competence for autogamy are reached almost simultaneously in all clones of the strains studied with the exception of about 1/3 of the A-31 clones in which autogamy occurs significantly earlier than conjugation. The results are discussed from the genetic point of view and in relation to the sexual mechanisms operating in nature within different populations of the species.     

The Species Problem in a Ciliate with a High Multiple Mating Type System, Euplotes crassus

ABSTRACT. One hundred twenty non-autogamous wild-type strains of Euplotes crassus , collected over seven years, mainly from the Mediterranean coasts, were investigated for their mating interactions. The strains were mixed pair-wise and data from mating reactions were evaluated and organized by means of a specially constructed computer program. The program identified 38 strains with distinctive mating patterns which could be clustered in nine clumps, all of which were connected either directly or indirectly. Thus, all these strains appeared to be components of the same gene pool, even though direct genetic exchange between strains was not possible in every combination. Subsequently, the 38 strains were subjected to cytometric analysis and scored for zymic variations resulting from electrophoretic patterns of five enzyme systems (acid phosphatases, amylases, malic dehydrogenase, malic enzyme, and tetrazolium oxidases) of proved diagnostic value in the identification of Euplotes species. No significant discontinuities correlated with mating patterns was apparent from these analyses. It was concluded that the E. crassus strains analyzed are not properly divided in sibling species and it was consistently suggested to avoid a genetic partitioning of ciliate species endowed with high multiple mating type systems, in which the sets of wild strains brought under investigation with difficulty represent the natural dimensions of the species.     

An Integrated Study of the Species Problem in the Euplotes crassus-minuta-vannus Group1

ABSTRACT. In an attempt to solve the ambiguity in the taxonomy of the Euplotes crassus, minuta, and vannus group, 19 strains were tested for mating interactions, electrophoresed for isozymic variations, and analyzed by multivariate morphometrics of the conventional diagnostic traits. The overall results supported the validity of the three named species. Inter-specific mating occurred only in a few crassus x vannus strain combinations and was usually inviable. Isozymic variations, in particular of amylases, malic enzyme, and malic dehydrogenase, were very restricted within conspecific strains and were great between non-conspecifics. The species ascertainment of the strains was possible on the basis of clustering and principal component analyses of morphological measures.     

Chemical Signaling in Ciliates

ABSTRACT. For long, our knowledge of the biology of ciliate pheromones has long relied solely upon the study of the two structurally unrelated "gamones" identified in culture filtrates of a Blepharisma species. However, the characterization of a number of polypeptide pheromones secreted by Euplotes raikovi and E. octocarinatus has now established that structural relationships of homology usually link these molecules, which is consistent with the genetic basis of the mating type systems evolved by these species. In this context, our growing appreciation of the conserved and variable elements of the pheromone architecture should foster progress in the understanding of pheromone-receptor interactions and thus, provide important clues into pheromone mechanisms of action.