Recent advances in molecular technology have revolutionized research on all aspects of the biology of organisms, including ciliates, and created unprecedented opportunities for pursuing a more integrative approach to investigations of biodiversity. However, this goal is complicated by large gaps and inconsistencies that still exist in the foundation of basic information about biodiversity of ciliates. The present paper reviews issues relating to the taxonomy of ciliates and presents specific recommendations for best practice in the observation and documentation of their biodiversity. This effort stems from a workshop that explored ways to implement six Grand Challenges proposed by the International Research Coordination Network for Biodiversity of Ciliates (IRCN‐BC). As part of its commitment to strengthening the knowledge base that supports research on biodiversity of ciliates, the IRCN‐BC proposes to populate The Ciliate Guide, an online database, with biodiversity‐related data and metadata to create a resource that will facilitate accurate taxonomic identifications and promote sharing of data.

The crystal structure of the pheromone Er-I from the unicellular eukaryotic organism Euplotes raikovi was determined at 1.6 A resolution and refined to a crystallographic R factor of 19.9%. In the tightly packed crystal, two extensive intermolecular helix-helix interactions arrange the Er-i molecules into layers. Since the putative receptor of the pheromone is a membrane-bound protein, whose extracellular C-terminal domain is identical in amino acid sequence to the soluble pheromone, the interactions found in the crystal may mimic the pheromone-receptor interactions as they occur on a cell surface. Based on this, we propose a model for the interaction between soluble pheromone molecules and their receptors. In this model, strong pheromone-receptor binding emerges as a consequence of the cooperative utilization of several weak interactions. The model offers an explanation for the results of binding studies and may also explain the adhesion between cells that occurs during mating.Pheromones from the ciliated protozoan Euplotes raikovi are proteins of 37-40 amino acids that function both as growth factors and as signaling molecules in cellular adhesion during mating (1-3). Over a dozen different cell types of E. raikovi have been identified based on their ability to form mating pairs (1). In the presence of only one cell type, the homologous secreted Er (Er-x = E. raikovi pheromone of type x) molecules stimulate growth of the cells by binding to cell-surface receptors in an autocrine fashion. In the presence of two different cell types or just one cell type to which heterologous pheromone has been added, Er molecules also stimulate cell adhesion between mating pair partners presumably by binding to the same cell-surface receptors (2, 3) in a paracrine manner. The putative receptors of the pheromones are membranebound proteins whose extracellular C-terminal domain is identical in amino acid sequence to the soluble pheromones (4). They arise by alternate splicing of the transcripts of the same gene that carries the information for the soluble pheromone (4).Different cell types can also be distinguished by the amino acid sequence of their pheromones. Sequences from nine different cell types have been determined (5-8), yielding seven unique sequences with pairwise sequence identities ranging from about 25% to 95%. Only seven residues are conserved among all sequences; these are the N-terminal aspartic acid and six cysteines that are involved in formation of three disulfide bridges (9).The NMR structures of three of the pheromones (Er-1, Er-2, and Er-10) have been determined and compared to each other (10-13). They revealed the three-helical bundle fold of the proteins and the orientations for about two-thirds of the side chains. The crystal structure reported here offers a detailed picture of the monomer and reveals two types of interactions between molecules that provide the basis for a model for receptor recognition, cell adhesion, and signaling. (14) is 1.53 A3/Da and the solvent content of the crystals is ...

Most organisms oppose many environmental stresses by rapidly enhancing synthesis of the highly conserved Hsp70 family of heat-shock proteins. Two ciliates which are endemic in Antarctic coastal seawater, Euplotes focardii and E. nobilii, and behave as psychrophile and psychrotroph micro-organisms, respectively, revealed a divergence in the capacity to respond to thermal stress with an activation of the transcription of their hsp70 genes. In both species, these genes were shown to be represented by thousands of copies in the cell's somatic functional nucleus (macronucleus). However, while a strong transcriptional activity of hsp70 genes was induced in E. nobilii cells transferred from 4 to 20 degrees C, a much smaller increase was revealed in heat-shocked cells of E. focardii. These findings suggest a closer adaptation to the stably cold Antarctic waters in the genetic response of E. focardii to thermal stress.

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.

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