Structure and expression of the Euplotes raikovi macronuclear pheromone genes

Euplotes (and reasonably other ciliates as well) has very proficiently invested in its pheromone/mating-type systems to control both the basic (quantitative and qualitative) aspects of life, i. e., reproduction and sex. To reproduce (i. e., multiply mitotically), or to mate (i. e., engage in a sexual process with inevitable detriment to reproduction) is an alternative that cells can apparently decide in relation to which type of pheromone-receptor association, i. e., autocrine versus paracrine, turns out (in the time and space) to be more effective on their surface. The nearly one hundred species of Euplotes all evolved multiple mating types. Based on analyses of Mendelian genetics, these mating types have for long been assumed to be determined by multi-allelic series of genes inherited at a single genetic locus (i.e., the mating-type or mat locus) and deputed at the synthesis of mating type-specific signaling proteins. The chemical characterization of these signaling proteins (known as pheromones) from an array of Euplotes species has now permitted to evolve in the study of Euplotes mating types from an approach of Mendelian genetics to an approach of molecular genetics. In this new experimental context, my PhD work was directed to clone and characterize the full-length macronuclear pheromone genes from different mating types of E. raikovi and to study their mechanisms of expression. Up to now, only one gene encoding the deviant pheromone family member, Er-23, has been completely characterized in E. raikovi. Additional information on the structure of other E. raikovi pheromone genes has been derived from analyses of cDNA clones isolated from type-I cells, as well as from the determination, by PCR amplification, of the pre-pro-Er-2 and pre-pro Er-10 coding regions [...]. The results obtained in my PhD research provide new insights into this topics, since ten different macronuclear genes coding for closely homologous pheromones were identified and their mechanism of expression characterized. As previously observed in E. nobilii, a species which is phylogenetically closely related to E. raikovi [...], the E. raikovi pheromone genes appear to be structurally highly conserved, in particular at the level of their 5' regions. In addition, analyses of their mechanism of expression suggest that this mechanism is much more complex than previously thought, since multiple mRNA's are generated not only in relation to the activity of multiple sites of the initiation of the transcription, but also in relation to the removal of introns from the conserved 5' regions