Nuclear Roles in the Post-Conjugant Development of the CiliateEuplotes aediculatusII. Experimentally Induced Regeneration of Old Macronuclear Fragments1

Conjugation in Euplotes raikovi (Protista, Ciliophora): New Insights into Nuclear Events and Macronuclear Development from Micronucleate and Amicronucleate Cells

Ciliates form a distinct group of single-celled eukaryotes that host two types of nuclei (micro and macronucleus) in the same cytoplasm and have a special sexual process known as conjugation, which involves mitosis, meiosis, fertilization, nuclear differentiation, and development. Due to their high species diversity, ciliates have evolved different patterns of nuclear events during conjugation. In the present study, we investigate these events in detail in the marine species Euplotes raikovi. Our results indicate that: (i) conjugation lasts for about 50 h, the longest stage being the development of the new macronucleus (ca. 36 h); (ii) there are three prezygotic micronuclear divisions (mitosis and meiosis I and II) and two postzygotic synkaryon divisions; and (iii) a fragment of the parental macronucleus fuses with the new developing macronucleus. In addition, we describe for the first time conjugation in amicronucleate E. raikovi cells. When two amicronucleate cells mate, they separate after about 4 h without evident nuclear changes; when one amicronucleate cell mates with a micronucleate cell, the micronucleus undergoes regular prezygotic divisions to form migratory and stationary pronuclei, but the two pronuclei fuse in the same cell. In the amicronucleate cell, the parental macronucleus breaks into fragments, which are then recovered to form a new functional macronucleus. These results add new information on the process of conjugation in both micronucleate and amicronucleate Euplotes cells.

Developmental and genetic effects of alcian blue in conjugating Tetrahymena thermophila: doublet formation and macronuclear retention

Genetic, kinetical and cortical effects of treatment with the inducer of mucocyst release, alcian blue (AB), on conjugating pairs of Tetrahymena thermophila are reported. AB induces the formation of doublet cells from pairs, and the majority of them are homopolar doublets. We present a model in order to explain the origin of these cells. Macronuclear retention (MR) is the most important genetic effect observed. Two kinds of MR can be obtained: prezygotic-MR (uniparental micronucleus) and postzygotic-MR (cross-fertilized micronucleus). Within the first group, both homokaryon and heterokaryon cells are obtained. From some abnormal conjugational configurations and the results of conjugational kinetic analysis we propose an explanation for the origin of MR cells induced by AB. Genetic effects obtained after AB treatment at different conjugational times are independent of the cortical ones. The utility of these different effects in genetical and physiological studies is discussed.