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A Vallesi

Publications and source records attributed to A Vallesi.

10 recordsLinked to original sources
PubMed2006

The cell type-specific signal proteins (pheromones) of protozoan ciliates.

In association with their mechanisms of self/non-self recognition (known as mating type systems), ciliates synthesize and constitutively secrete cell type-specific proteins into their extracellular medium. These proteins, designated as pheromones, have been isolated from species of Euplotes and shown to be members of families of structurally homologous molecules, all rich in intra-chain disulfide bonds and organized exclusively in helical conformation. Due to their similar architectures, they can interact with their membrane receptors in competition with one another and bind effectively to their cells of origin in autocrine fashion, or to other co-specific cells in paracrine fashion. In the former case, they promote the vegetative cell growth; in the latter, they induce cells to temporarily arrest their growth stage and shift to a mating (sexual) stage. These varied, context-dependent activities of ciliate pheromones imply an early evolution of basic properties of animal growth factors and cytokines in the unicellular eukaryotes.

Animals↗
PubMed2000

The autocrine mitogenic loop of the ciliate Euplotes raikovi: the pheromone membrane-bound forms are the cell binding sites and potential signaling receptors of soluble pheromones.

Homologous proteins, denoted pheromones, promote cell mitotic proliferation and mating pair formation in the ciliate Euplotes raikovi, according to whether they bind to cells in an autocrine- or paracrine-like manner. The primary transcripts of the genes encoding these proteins undergo alternate splicing, which generates at least two distinct mRNAs. One is specific for the soluble pheromone, the other for a pheromone isoform that remains anchored to the cell surface as a type II protein, whose extracellular C-terminal region is structurally equivalent to the secreted form. The 15-kDa membrane-bound isoform of pheromone Er-1, denoted Er-1mem and synthesized by the same E. raikovi cells that secrete Er-1, has been purified from cell membranes by affinity chromatography prepared with matrix-bound Er-1, and its extracellular and cytoplasmic regions have been expressed as recombinant proteins. Using the purified material and these recombinant proteins, it has been shown that Er-1mem has the property of binding pheromones competitively through its extracellular pheromone-like domain and associating reversibly and specifically with a guanine nucleotide-binding protein through its intracellular domain. It has been concluded that the membrane-bound pheromone isoforms of E. raikovi represent the cell effective pheromone binding sites and are functionally equipped for transducing the signal generated by this binding.

Amino Acid Sequence↗
PubMed1998

Structure-function relationships of pheromones of the ciliate Euplotes raikovi with mammalian growth factors: cross-reactivity between Er-1 and interleukin-2 systems.

Diffusible protein signals of the ciliate Euplotes raikovi, denoted as pheromones, have functionally been linked with prototypic growth factors of animal cells by the demonstration that they not only induce a temporary cell union in mating pairs, by acting in a paracrine-like fashion, but can also bind to cells in autocrine fashion and promote their vegetative (mitotic) proliferation. It is now shown that pheromone Er-1 is capable of binding to the alpha and beta chains of the multimeric IL-2 receptor on mammalian cells and that IL-2 can, in turn, bind to the putative cell receptor of this pheromone. Similarities in the IL-2 and Er-1 structures support these findings and raise controversial implications with regard to their evolutionary significance.

Amino Acid Sequence↗
PubMed1996

Ciliate pheromones.

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Amino Acid Sequence↗
PubMed1995

Autocrine mitogenic activity of pheromones produced by the protozoan ciliate Euplotes raikovi.

Diffusible polypeptide pheromones (formerly referred to as mating-type factors, sex factors or gamones), which distinguish otherwise morphologically identical vegetative cell (mating) types from one another, are produced by some species of ciliates. Their most striking effect can be observed by exposing cells of one type to a pheromone secreted by another co-specific cell type. In the presence of this 'non-self' signal, these cells interrupt their vegetative life to unite temporarily in mating pairs. Thus ciliate pheromones have traditionally been associated only with mating induction. However, the identification of autocrine pheromone receptors suggests a broader role, which is supported by the hypothesis that ciliates evolved their mating-type mechanism for pursuing self-recognition. We now report studies, in the cosmopolitan marine sand-dwelling protozoan ciliate Euplotes raikovi, demonstrating that these molecules promote the vegetative reproduction (mitogenic proliferation or growth) of the same cells from which they originate. As, understandably, such autocrine pheromone activity is primary to that of targeting and inducing a foreign cell to mate (paracrine functions), this finding provides an example of how the original function of a molecule can be obscured during evolution by the acquisition of a new one.

Amino Acid Sequence↗
PubMed1992

Primary structure of Euplotes raikovi pheromones: comparison of five sequences of pheromones from cells with variable mating interactions.

The amino acid sequences of five pheromones, Er-2, Er-3, Er-9, Er-11, and Er-20, secreted by cells of different mating types of the ciliated protozoa Euplotes raikovi, have been determined by automated Edman analyses of the whole proteins and germane fragments. In each case, the molecular mass was determined by plasma desorption or laser desorption mass spectrometry and was in excellent agreement with the calculated values. Where available, the determined sequences were also in accord with the corresponding segments of the precursor molecules predicted from relevant nucleic acid sequences. Of the five, two were found to be identical (Er-2 and Er-9) and one (Er-3) was identical to a pheromone previously sequenced (Er-1), even though mating pair formation was found to take place (although to a limited extent) when cells secreting those pheromones were combined in a mixture. Comparison of the five unique sequences suggested a closer relationship between Er-1 (Er-3) and Er-10 and between Er-11 and Er-20 (44% and 56% identity, respectively) than was generally observed among the other members. This pairing was also supported by hydrophobicity analyses. Interestingly, Er-20 cannot, as a rule, induce cell union in any of the other cell types, including cells secreting Er-11, despite the fact that Er-20 and Er-11 are the most similar of the five unique sequences. Thus sequence identity and secondary structure profiles are not a good indicator of biological relatedness as manifested in heterologous receptor interaction.

Amino Acid Sequence↗
PubMed1992

Developmental analysis of the cell recognition mechanism in the ciliate Euplotes raikovi.

Euplotes raikovi, like other ciliates, passes through a postconjugal immaturity, operatively identified by an apparent cell inability to form mating pairs under experimental conditions that are the same as those used for inducing mating at maturity. In cells homozygous for the gene mat-2, which controls the pheromone Er-2, Er-2 mRNA synthesis and mature Er-2 secretion were shown to start from the very beginning of the life cycle and continue throughout immaturity, although to extents estimated to be 5- to 10-fold lower than at maturity. In addition, experiments of 125I-Er-2 binding and crosslinking provided evidence that autocrine pheromone-binding sites, showing values of the dissociation constant of the order of 10(-9) M, are on the surface of immature cells. The number of these sites per cell was estimated to increase from less than 10(6) per cell of 5-7 fissions of age, to about 16 x 10(6) at maturity. These results were taken to suggest that a pheromone-receptor production is stimulated during immaturity by autocrine pheromone binding to cells and that this production might be essential for the development of a pheromone-receptor density high enough to transform the cell from "immature" to "adult," that is competent to respond as well to pheromones of conspecific, genetically different cells.

Animals↗
PubMedDate not supplied

Specific and common epitopes in mating pheromones of Euplotes raikovi revealed by monoclonal antibodies.

Polypeptide mating pheromones Er-1 and Er-2, purified from the supernatant of Euplotes raikovi cultures of mating type I and mating type II, respectively, were used to immunize mice and obtain monoclonal antibodies. Five hybridoma clones producing antibodies specific to the mating pheromones were selected. They were analyzed for immunospecificity by immunoperoxidase assay, immunoblotting, and for their efficacy in inhibition of mating pheromone activity. Monoclonal antibodies from two hybridoma clones recognized only the mating pheromone used as antigen: those from the other three clones reacted, to comparable extents, with both mating pheromones. On the basis of these results it was assumed that two immunogenic sites exist in Er-1 and Er-2, one specific and the other common to both mating pheromones.

Animals↗
PubMedDate not supplied

Chemical signaling in ciliates.

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.

Amino Acid Sequence↗