186,605 research outputs found
Self/nonself discrimination in ciliated Protozoa: the molecular basis. REPORT of the VIIIth meeting of the Italian Association for Developmental and Comparative Immunobiology (IADCI), Napoli.
No full textAs also a recent review in Cell on the "Quality
Control in Self/Nonself Discrimination" points out
(Boehm T. Cell 125: 845-858, 2006), comparative
studies of the mechanisms that avoid self-mating in
more ancient eukaryotes are thought to be of key
relevance for shedding light on the control of
specificity in self/nonself discrimination, as well as
on the evolutionary emergence of the antigen
receptors in the adaptive immune system. These
studies, however, traditionally drive most attention
on the self-incompatibility of plants, self-sterility and
allo-recognition of tunicates, mating types of fungi.
Scarce or no reference at all is made to ciliates.
Nevertheless, the ciliate highly multiple mating-type
systems are providing insightful information not only
on the molecular basis of self/nonself recognition in
more ancient organisms, but also on the central
question of how new receptor/ligand pairs are
generated in complex recognition systems.
This information essentially derives from: (i) NMR and crystallographic analyses (mostly carried
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out in collaboration with the Kurt Wuthrich’s laboratory at the ETH in Zurich) of the three-dimensional structures of a set of water-born protein signals (pheromones) produced by Euplotes species (Luporini et al. Curr. Pharm. Des. 12: 3015-3024, 2006), and (ii) the determination of the splicing mechanism by which the same cell controls its own specific diffusible signal and the (autocrine) binding receptor of this signal (Vallesi et al. Eukaryot. Cell 4: 1221-1227, 2005)
Variabilità elettroforetica nel gruppo di specie marine Euplotes crassus-minuta-vannus (CILIOPHORA, HYPOTRICHIDA).
No full textThe pheromone genes of the self/non-self recognition mechanism of the ciliate Euplotes crassus generate multiple transcripts by an alternative splicing of ‘matryoshka’ introns
No full textIn ciliates, cell-type distinctive protein pheromones control a self/non-self recognition mechanism responsible for the cell switching between the vegetative and sexual stages of the life cycle. These signaling molecules are encoded by genes (pheromone genes) that in the cell somatic nucleus (macronucleus) represent the transcriptionally active versions of transcriptionally silent genes allelic at the same genetic locus mat of the cell germinal nucleus (micronucleus). In the course of evolution, in Euplotes, the native single multiallelic mat locus underwent duplication among species which, such as E. crassus, form the latest branching clade of the phylogenetic tree. Because of this duplication, E. crassus expresses two distinct families of pheromone genes instead of a single family, as is the case in species of earlier branching clades.
We analyzed the structure and expression of a number of E. crassus pheromone genes representative of the two families. Like their orthologs of other Euplotes species, these genes show 5’-leader regions that are much more extended than the coding regions, lack canonical regulatory sequences for gene transcription, and synthesize multiple transcripts (in addition to the pheromone-specific one) through the activity of two distinct transcription start sites and a mechanism of alternative intron splicing. These E. crassus introns have been found to be unique with respect to introns of all the other Euplotes pheromone genes. They can be distinguished between ‘matryoshka’ introns, residing one inside the other like Russian Dolls, and ‘non-matryoshka’ introns. While the former possess canonical GTA/TAG splicing sites, the latter possess CTA/TAC splicing sites complementary to the canonical GTA/TAG splicing sites. This strongly suggests that both the DNA strands of the E. crassus pheromone genes can be used as template for transcription. We are currently attempting to verify this hypothesis and assign a function to the products of the multiple E. crassus pheromone gene transcripts
The often overlooked coming out of ciliates: biological and experimental benefits from accepting genetically identical conspecifics as sexual partners
No full textCiliates usually manifest sex in the form of conjugation, a unique phenomenon in which cells temporarily unite two by two in mating pairs to perform a mutual exchange of gamete-nuclei derived from meiotic products of their germinal micronucleus. The native view of conjugation as a spontaneous manifestation associated with environmental famine conditions was eventually denied by the milestone Sonneborn’s finding (PNAS, 1937) that the most popular ciliate, Paramecium, actually controls conjugation through a genetic mechanism of mating types. Being only two in the Paramecium species studied by Sonneborn, these mating types were functionally equated to ‘male’ and ‘female’ sexes. And, as a consequence of this equation, conjugation was since thought of as a phenomenon committed to involve, as a rule, genetically distinct cells representing two ‘complementary’ mating types. However, this is a wrong tenet adverse the evidence that many ciliates conjugate with no discrimination between sex identity and diversity. And from this no discrimination both the ciliate biology and the students of ciliate biology draw benefit. The ciliate biology, because the homo-sexual pairs (yet ineffective to reshuffle the species gene pool) multiply the opportunity for cells to practice conjugation which, in every case, determines the initiation of a new life cycle and the replacement of the cell ‘old’ transcriptionally active somatic (macronuclear) genome with a completely new one generated from the permanently ‘young’ transcriptionally inert germinal (micronuclear) genome. The students of ciliate biology, because homo-sexual pairs form without requiring physical interactions between sexually/genetically different cells. They form as well in cultures of cells of the same identity previously suspended with filtrates from cultures of conspecific cells of different identity. Which immediately identifies species that interact sexually via water-borne mating signals (pheromones), and greatly facilitates the isolation and function-structure characterization of these signals directly from cell-culture filtrates
Competizione tra diversi feromoni di Euplotes raikovi nell'interazione con uno stesso recettore. Atti del 55° Congresso Nazionale U.Z.I.
No full text
Evidence for the chimeric origin of a pheromone-coding gene in Euplotes raikovi
No full textCiliates, unique among eukaryotes, evolved two types of nucleus which are distinct in both structure and function. A diploid transcriptionally silent germline micronucleus (MIC) with an orthodox chromosomicstructure coexists in the same cytoplasm with a polyploid transcriptionally active somatic macronucleus (MAC) showing a unique sub-chromosomic structure. This structure is acquired in coincidence with every sexual event, when the ex-conjugant (or ex-autogamic) cell initiates a new life cycle developing a new MAC from a mitotic product of the synkaryon. In spirotrichous ciliates such as Euplotes, the chromosomes of this product undergo impressive phenomena of polytenization, fragmentation in thousands of DNA fragments known as ‘Macronuclear Destined Sequences’ (MDSs), and DNA elimination. Under the guide of noncoding RNA templates synthesized by the old MAC before being destroyed, theseMDSs are assembled into sub-chromosomic (‘gene-size’)DNA molecules which,amplified to thousands of copies, compose the new MAC.The way to a correct MDSassembly may be crossed by errors, with the consequent generation of functional chimeric genes which can stably be integrated and expressed in the MAC genome.One of these chimeric genes came to light by studying the genetic basis of the pheromone-mediated self/not-self recognition mechanism in E. raikovi. The genome of type I cells secreting pheromone Er-1 was found to contain two structurally distinct MAC Er-1 coding genes,both expressed via a mechanism of intron splicing responsible for the synthesis of the Er-1 soluble form and a membrane-bound Er-1 isoform functioning as autocrine pheromone receptor. The sequence of one gene resulted unmistakably homologous throughout its length with the sequences of other members of the E. raikovipheromone gene family. In contrast, the sequence of the second gene resulted unique at level of a 359-bp segment of the 5’ region destined to specify the cytoplasmic domain of the Er-1 membrane-bound isoform. By showing that this segment arises from a wrong assembly of a MDS destined to a 2417-bp gene with no relationship with the signaling pheromone system, we provide additional evidence that the generation of functionally active chimeric genesfrom not-programmed phenomena of somatic MDS recombination is an effective and MIC-independent source of gene variants in the ciliate MAC genome
Social Semiotic Stylistics and the corpus: How do-able is an automated analysis of verbal art?
No full textSocial Semiotic Stylistics and the corpus: How do-able is an automated analysis of verbal art?
Corpora have been extensively applied in all areas of linguistic research, including that of ‘figurative’ language (Charteris-Black 2004; Deignan 2005; Luporini 2013a) and to literature itself (e.g., Taylor Torsello and Turci 2007; Toolan 2009). Yet ‘high’ level studies of text in all registers, addressing semantics/context, have been shown to resist automation (Miller et al., to appear). And, when dealing with a framework for ‘verbal art’ (Hasan 1985 [1989]; 2007) that is so scrupulous in its precepts, categories and its very definition of the object of inquiry, the question of the extent to which automated corpus techniques can be effectively deployed must be tackled. Though corpus assisted studies should ideally be part of the ongoing development of a rigorous Social Semiotic Stylistics (SSS), the proposal is not unproblematic.
This chapter explores the problem, firstly by probing the implications of SSS’s essential theses, which we thoroughly endorse (cf. Miller 2010), in particular its conviction that literature is “[...] created by languaging in a particular way” (Hasan 2007: 16, original emphasis). This specialness of verbal art is what led Hasan to devising a unique model of ‘double articulation’ with both a semiotic system of language and a higher order semiotic system of verbal art, the level at which the first order meanings are enriched in order to express the literature text’s Theme (1985 [1989]). We argue that, while corpus tools may assist analysis at the lower level semiotic system of language itself, and even potentially help identify motivated patterns to be further examined, verbal art’s higher order semiosis requires traditional qualitative manual analysis of a logogenetic nature.
The second part of the chapter summarises the results of a corpus-assisted reading of J.M Coetzee’s 1986 novel Foe (Luporini 2013b), a rewriting of Defoe’s Robinson Crusoe (Widdowson 2006 ), with a view to illustrating what software such as WordSmith Tools (Scott 2008) can/cannot tell us about: a) its thematic richness, and b) the complex cultural context in which it was produced and which it, in turn, symbolically reproduces: Apartheid South Africa.
Cited References
Charteris-Black, J. (2004). Corpus Approaches to Critical Metaphor Analysis. Basingstoke: Palgrave Macmillan.
Deignan, A. (2005). Metaphor and Corpus Linguistics. Amsterdam and Philadelphia: John Benjamins.
Hasan, R. (1985 [1989]). Language, Linguistics and Verbal Art. Geelong, Vic.: Deakin University Press; Oxford: Oxford University Press.
Hasan, R. (2007). “Private pleasure, public discourse: reflections on engaging with literature”, in Miller, D.R. and Turci, M. (eds.), pp. 13-40.
Luporini, A. (2013a). Metaphor in Times of Crisis: Metaphorical Representations of the Global Crisis in The Financial Times and Il Sole 24 Ore 2008. Unpublished doctoral dissertation. University of Pisa.
Luporini, A. (2013b). “Inside ‘the home of Friday’: Linguistic representations of frustrated communication in a corpus-assisted study of J.M. Coetzee's Foe”, in Di Michele, L. (ed.), Regenerating Community, Territory, Voices. Memory and Vision. Proceedings of the XXV AIA Conference, L'Aquila, September 15-16-17, 2011. Volume II. Naples: Liguori Editore, pp. 186-198.
Miller, D.R., Bayley, P., Bevitori, C., Fusari, S. and Luporini, A. (to appear, online). ‘Ticklish trawling’: The limits of corpus assisted meaning analysis – a colloquium in four parts. Extended abstract of the colloquium presented at the 24th European Systemic Functional Linguistics Conference and Workshop, Coventry, 1-3 July, 2013.
Miller, D.R. and Turci, M. (eds.) (2007). Language and Verbal Art Revisited. Linguistic Approaches to the Study of Literature. London: Equinox.
Scott, M. (2008). WordSmith Tools version 5. Liverpool: Lexical Analysis Software.
Taylor Torsello, C. (2007) “Projection in literary and in non-literary texts”, in Miller, D.R. and Turci M., pp. 115-148.
Toolan M. (2009) Narrative Progression in the Short Story, a corpus stylistic approach. Amsterdam and Philadelphia: John Benjamins.
Turci M. (2007) “The meaning of ‘dark*’ in Joseph Conrad’s Heart of Darkness”, in in Miller, D.R. and Turci, M. (eds.), pp. 97-114.
Widdowson, P. (2006). “’Writing back’: contemporary re-visionary fiction”. Textual Practice 20 (3), pp. 491-507
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