| Summary: | Ciliates are unique in having nuclear dimorphism (i.e., possessing both a germline micronucleus and a somatic macronucleus in one cell), and undergo dramatic changes during their sexual process (known as conjugation). Here we investigate the nuclear events and morphogenetic processes during conjugation in the freshwater species Euplotes aediculatus. In addition, three conjugation-related pheromone genes were sequenced and analyzed. The results indicate that: (i) the 65-hour-long conjugation process includes five nuclear divisions, i.e., three prezygotic divisions (mitosis, meiosis I and II) and two postzygotic divisions; (ii) the ciliature reorganizes twice during conjugation with the frontoventral-transverse cirral anlagen regenerating during both morphogenetic events and breaking apart in a 3:3:3:2:2 pattern; and (iii) each of three pheromone genes contains a 444 bp coding region and encodes 147 amino acid polypeptides. These results suggest a broadly shared morphogenetic pattern during conjugation in Euplotes species and provide new information for studies on the evolutionary history of pheromone genes.
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