Maintenance of heterozygosity at the mt locus after autogamy in Euplotes minuta (Ciliata Hypotrichida).

The genetic consequences of autogamy have been analysed in the autogamous strain A-25 of E. minuta. During autogamy as well as during conjugation four pronuclei (two genetically identical pairs) are formed in each individual. In conjugating pairs, any two of the four pronuclei of the autogamous conjugant may participate in synkaryon formation. Consequently, an 8:13 segregation ratio of clonal and synclonal mating-type inheritance has been found to occur in the progeny obtained by crossing A-25 animals with non-autogamous animals. During autogamy, synkaryon formation appears to be brought about by a preferential karyogamy of genetically dissimilar nuclei more often than is expected on a random basis. Therefore, heterozygosity is usually maintained after autogamy in spite of the extreme inbreeding characteristics of this sexual process

Ciliate Mating Types and Pheromones

The story of our knowledge of ciliate mating types and their relevant signaling molecules, originally referred to as mating type substances/factors and today usually described as pheromones (to imply a more general function as chemicals used to communicate between individuals of the same species), is inextricably bound to our understanding about ciliate sexual activity. This activity is commonly manifested as conjugation, autogamy in ciliates, like parthenogenesis in animals, being an additional and much more sporadic alternative. Although conjugation has been described in a variety of organisms, ciliate conjugation is a unique phenomenon of cell-cell interaction and reversible union in mating pairs, that has nothing to do with phenomena of gamete-gamete interaction and irreversible union into a synkaryon. The two ciliates (designated as gamonts) which unite into a conjugal, or mating pair are de facto hermaphrodite, vegetatively reproducing cells which will generate two sexually complementary haploid gametic nuclei, one migratory (male) and one stationary (female), only as result of a meiotic process that involves their diploid micronuclei and is triggered by the cell mating union itself

Characterization and Expression of the Gene Encoding En-MAPK1, an Intestinal Cell Kinase (ICK)-like Kinase Activated by the Autocrine Pheromone-Signaling Loop in the Polar Ciliate, Euplotes nobilii

In the protozoan ciliate Euplotes, a transduction pathway resulting in a mitogenic cell growth response is activated by autocrine receptor binding of cell type-specific, water-borne signaling protein pheromones. In Euplotes raikovi, a marine species of temperate waters, this transduction pathway was previously shown to involve the phosphorylation of a nuclear protein kinase structurally similar to the intestinal-cell and male germ cell-associated kinases described in mammals. In E. nobilii, which is phylogenetically closely related to E. raikovi but inhabits Antarctic and Arctic waters, we have now characterized a gene encoding a structurally homologous kinase. The expression of this gene requires +1 translational frameshifting and a process of intron splicing for the production of the active protein, designated En-MAPK1, which contains amino acid substitutions of potential significance for cold-adaptation

Euplotes pheromones

Species of Euplotes secrete protein signals (pheromones) in relation with their mating-type mechanisms of self-nonself recognition. Significant numbers of these pheromones have been characterized to varied extents of structural complexity in E. raikovi, E. nobilii, and E. octocarinatus. In every case, they form species-specific families of structurally homologous, cysteine-rich proteins. In E. raikovi, these proteins have been shown to share a common architecture based on a three-helix bundle, that permits them to bind to cells in competition with one another and elicit varied, context-dependent responses

Structural characterization of a protein pheromone from a cold-adapted (Antarctic) single-cell eukaryote, the ciliate Euplotes nobilii

Free-living species of ciliated Protozoa control their vegetative (mitotic) proliferation and mating (sexual) processes by diffusible, cell type-specific protein signals (pheromones). One of these molecules, designated En-2, was isolated from a species, Euplotes nobilii, living in the stably cold marine waters of Antarctica, and its complete amino acid sequence of 60 residues was determined by automated Edman degradation of the whole protein and peptides generated by trypsin digestion. The proposed sequence is : DIEDFYTSETCPYKNDSQLA20- WDTCSGGTGNCGTVCCGQCF40SFPVSQSCAGMADSNDCPNA60. The En-2 structure appears to be characterized by an adaptive insertion of a glycine-rich motif potentially capable to confer more flexibility to a functionally critical region of the molecule

Structural characterization of En-1, a cold-adapted protein pheromone isolated from the Antarctic ciliate Euplotes nobilii.

The second of two diffusible cell signal proteins (pheromones) purified from a wild-type strain of the Antarctic ciliate, Euplotes nobilii, has been determined by automated Edman degradation of the whole molecule and peptides generated by its chymotryptic digestion. The proposed sequence of 52 amino acids of this new pheromone, designated En-1, is: NPEDWFTPDT10CAYGDSNTAW20TTCTTPGQTC30YTCCSSCFDV40VGEQACQMSA50QC. In common with the previously determined 60-amino-acid sequence of the other pheromone, En-2, it bears eight cysteines in conserved positions (presumably linked into four conserved intrachain disulfide bonds), and physicochemical features of potential significance for cold adaptation, such as a reduced hydrophobicity, an increased solvent accessibility, and an improved local backbone flexibility. However, En-1 diverges from En-2 for having evolved a threonine cluster in the place of a glycine cluster to apparently make more flexible a region that is likely functionally important

Purification and initial characterization of two pheromones from the marine Antartic cilate, Euplotes nobilii

Among a set of wild-type strains of Euplotes nobilii, every one derived asexually from one specimen isolated from Terra Nova Bay (Ross Sea, Antarctica), two were found to be representative of different mating types mutually capable of inducing each other to form mating pairs through pheromones constitutively secreted into the extracellular environment. Pheromones of strain AC-1 were purified to homogeneity and shown to be represented by two distinct proteins, that were denoted En-1 and En-2. En-1, secreted in amounts three-fold greater than En-2, was determined to have a molecular weight of 5617 and an asparagine at the N-terminus of its amino acid sequence, while En-2 has a molecular weight of 6290 and bears an asparctic acid at its N-terminus. The fact that En-1 and En-2 are coreleased by genetically identical cells of the same strain was taken to imply that they carry a heterozygotic combination of allelic pheromone genes and that these genes are regulated by relationships of co-dominance

Genetic relationships in bipolar species of the protist ciliate, Euplotes

Protists thrive in polar oceans, where they represent a major driving force for globally important biogeochemical cycles and a key food-web component. Their biogeography is frequently associated to bipolar patterns of distribution. Although conceptually well supported by apparently unrestricted migration rates, the experimental certification of these patterns copes with the protist paucity of morphological characters with taxonomic value and difficulties in applying conventional species concepts. We studied three marine species of the ciliate Euplotes, E. euryhalinus, E. nobilii, and E. petzi, for their bipolar distribution by comparing the SSU-rRNA gene sequences and mating interactions of Antarctic, Patagonian, and Arctic strains. Each species was analogously found not to carry significantly varied SSU-rRNA gene sequences, implying a common occurrence of trans-equatorial genetic mixing. However, mating analyses revealed significant inter-species differences. Scarce Antarctic x Arctic strain mating compatibility distinguished E. petzi from E. euryhalinus and E. nobilii, in which mating pairs between Antarctic and Arctic strains were successfully induced. Yet, E. nobilii was the only one of the two species to show cross-fertilizing and fertile mating pairs. Taking the biological concept of species as discriminatory, it was thus concluded that only E. nobilii warrants the definition of genuine bipolar species