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Ciliates are a rich source of molecules synthesized to socialize, compete ecologically, and interact with prey and predators. Their isolation from laboratory cultures is often straightforward, permitting the study of their mechanisms of action and their assessment for applied research. This review focuses on three classes of these bioactive molecules: (i) water‐borne, cysteine‐rich proteins that are used as signaling pheromones in self/nonself recognition phenomena; (ii) cell membrane‐associated lipophilic terpenoids that are used in interspecies competitions for habitat colonization; (iii) cortical granule‐associated molecules of various chemical nature that primarily serve offence/defense functions. [ABSTRACT FROM AUTHOR]

In Euplotes raikovi, we have determined the full‐length sequences of a family of macronuclear genes that are the transcriptionally active versions of codominant alleles inherited at the mating‐type (mat) locus of the micronuclear genome, and encode cell type‐distinctive signaling pheromones. These genes include a 225–231‐bp coding region flanked by a conserved 544‐bp 5′‐leader region and a more variable 3′‐trailer region. Two transcription initiation start sites and two polyadenylation sites associated with nonconventional signals cooperate with a splicing phenomenon of a 326‐bp intron residing in the 5′‐leader region in the generation of multiple transcripts from the same gene. In two of them, the synthesis of functional products depends on the reassignment to a sense codon, or readthrough of a strictly conserved leaky UAG stop codon. That this reassignment may take place is suggested by the position this codon occupies in the transcripts, close to the transcript extremity and far from the poly(A) tail. In such a case, one product is a 69‐amino acid protein in search of function and the second product is a 126‐amino acid protein that represents a membrane‐bound pheromone isoform candidate to function as a cell type‐specific binding site (receptor) of the soluble pheromones. [ABSTRACT FROM AUTHOR]

The high-multiple mating system of Euplotes crassus is known to be controlled by multiple alleles segregating at a single locus and manifesting relationships of hierarchical dominance, so that heterozygous cells would produce a single mating-type substance (pheromone). In strain L-2D, now known to be homozygous at the mating-type locus, we previously identified two pheromones (E c-α and E c-1) characterized by significant variations in their amino acid sequences and structure of their macronuclear coding genes. In this study, pheromones and macronuclear coding genes have been analyzed in strain POR-73 characterized by a heterozygous genotype and strong mating compatibility with L-2D strain. It was found that POR-73 cells contain three distinct pheromone coding genes and, accordingly, secrete three distinct pheromones. One pheromone revealed structural identity in amino acid sequence and macronuclear coding gene to the E c-α pheromone of L-2D cells. The other two pheromones were shown to be new and were designated E c-2 and E c-3 to denote their structural homology with the E c-1 pheromone of L-2D cells. We interpreted these results as evidence of a phenomenon of gene duplication at the E. crassus mating-type locus, and lack of hierarchical dominance in the expression of the macronuclear pheromone genes in cells with heterozygous genotypes. [ABSTRACT FROM AUTHOR]

Nuclear (18S and ITS) and mitochondrial (16S) ribosomal RNA gene sequences were determined from genetically distinct wild-type strains of Antarctic (nine strains), Fuegian (four strains), Greenland (nine strains) and Svalbard (three strains) populations of the marine ciliate, Euplotes nobilii, and analysed for their nucleotide polymorphisms. A close genetic homogeneity was found within and between the Antarctic and Fuegian populations, while more significant levels of genetic differentiation were detected within and between the two Arctic populations, as well as between these populations and the Antarctic/Fuegian ones. The phylogeographical pattern that was derived from these data indicates that gene flow is not limited among Arctic populations; it equally connects the Arctic and Antarctic populations either directly, or through the Fuegian population. This indication reinforces previous evidence from laboratory assays of mating interactions between some of the strains analysed in this work that Southern and Northern polar populations of E. nobilii belong to a unique, panmictic population that substantially share the same gene pool. [ABSTRACT FROM AUTHOR]

Ciliates comprise species synthesizing water-diffusible mating type factors or pheromones and species synthesizing insoluble, cell membrane-bound pheromones. Euplotes crassus has traditionally been placed in the latter group. In contrast with this notion, we found that E. crassus is a constitutive pheromone-secreting ciliate, like other Euplotes species. From cell-free filtrate preparations of the E. crassus strain L-2D, we isolated two distinct pheromones, designated as E c-α and E c-1, and determined their complete amino acid sequences by combined chemical and genetic approaches. The E c-α pheromone sequence extends for 56 amino acid residues with six cysteines and shows a molecular mass of 6,183 Da, while the E c-1 pheromone sequence extends for 45 amino acid residues with 10 cysteines and shows a molecular mass of 4,840 Da. Marked structural differences distinguish the full-length E c-α and E c-1 coding sequences, which have been cloned and characterized from the transcriptionally active macronuclear genome. They were taken as clear indication that the E c-α and E c-1 pheromones are specified by genes that are not allelic, but likely derived from a duplicated genetic locus of the transcriptionally silent micronuclear genome. [ABSTRACT FROM AUTHOR]

Unique opportunities are provided by phylogenetically closely related organisms thriving in stably cold, or temperate milieus to study adaptive modifications of structurally homologous molecules. These modifications are of keen interest in basic science as well as in biotechnology. This review highlights structural and functional specificities that differentiate two homologous families of psychrophilic and mesophilic water-borne proteins (designated as pheromones) that signal mitotic growth and sexual mating in two marine species of the protozoan ciliate Euplotes, i.e., E. nobilii, which is distributed in Antarctic and Arctic waters, and E. raikovi, which inhabits temperate waters. The two protein families show strict conservation of a common three-helix bundle in a compact core of the molecular structure, which provides long-lasting integrity and biological activity to these molecules in their natural environment. In the psychrophilic pheromone family, cold-adaptation appears to have been achieved by superimposing an integrated complex of structural modifications on this conserved scaffold. Functionally most relevant appear to be extensions of polypeptide segments devoid of regular secondary structures, a specific distribution of polar and hydrophobic amino acids, the presence of solvent-exposed clusters of negatively charged amino acid side chains, and a unique role of aromatic residues in anchoring the molecular architecture. Due to these modifications, the psychrophilic pheromones are an example of an elegant combination of high stability of the three-dimensional structures with sufficient structural plasticity for efficient functioning at their physiologically low temperatures. © 2009 IUBMB IUBMB Life 61(8): 838–845, 2009 [ABSTRACT FROM AUTHOR]

Euplotes is diversified into dozens of widely distributed species that produce structurally homologous families of water-borne protein pheromones governing self-/nonself-recognition phenomena. Structures of pheromones and pheromone coding genes have so far been studied from species lying in different positions of the Euplotes phylogenetic tree. We have now cloned the coding genes and determined the NMR molecular structure of four pheromones isolated from Euplotes petzi, a polar species which is phylogenetically distant from previously studied species and forms the deepest branching clade in the tree. The E. petzi pheromone genes have significantly shorter sequences than in other congeners, lack introns, and encode products of only 32 amino acids. Likewise, the three-dimensional structure of the E. petzi pheromones is markedly simpler than the three-helix up-down-up architecture previously determined in another polar species, Euplotes nobilii, and in a temperate-water species, Euplotes raikovi. Although sharing the same up-down-up architecture, it includes only two short α-helices that find their topological counterparts with the second and third helices of the E. raikovi and E. nobilii pheromones. The overall picture that emerges is that the evolution of Euplotes pheromones involves progressive increases in the gene sequence length and in the complexity of the three-dimensional molecular structure. [ABSTRACT FROM AUTHOR]