Update on the molecular genetics of Paramecium

Ichthyophthirius multifiliis Fouquet and Ichthyophthiriosis in Freshwater Teleosts

The ciliate Ichthyophthirius multifiliis is an important pathogen of freshwater teleosts occurring in both temperate and tropical regions throughout the world. The disease, ichthyophthiriosis, accounts for significant economic losses to the aquaculture industry, including the ornamental fish trade, and epizootics in wild fish populations can result in mass kills. This review attempts to provide a comprehensive overview of the biology of the parasite, covering the free-living and parasitic stages in the life cycle, host-parasite interactions, and the immune response of host and immune evasion strategies by the parasite. Emphasis on the immunological aspects of infection within the fish host, including molecular studies of i-antigens, reflects the current interest in this subject area and the quest to develop a recombinant vaccine against the disease. The current status of methods for the control of ichthyophthiriosis is discussed, together with new approaches in combating this important disease.

Clonal and temperature induced differences in serotypes in the ciliate Dileptus anser

Antigenic differences have been demonstrated in 20 clones of the ciliate Dileptus anser by immobilization assay, precipitation reaction in agar and immunofluorescence, using antisera obtained against two of these clones. Homologous clones reacted with antisera in high dilutions. 7 heterologous clones demonstrated a slight reaction of immobilization. 13 heterologous clones failed to react with immune sera, which allowed to attribute them to some other serotypes. By immunodiffusion methods the presence of an antigen expressed in a single clone has been shown. When testing a certain clone with the homologous immune serum by immobilization reaction and immunofluorescence, the subclones cultured at 17°C and 25°C express two different serotypes each. When cultivating the same clone at 19 °C, 21 °C or 23 °C, the cells express both of these serotypes, although to a different extent depending on the temperature of their cultivation. Heterologous clones often show cross-reactions with the same immune sera, usually when the ciliates are cultivated at the same temperature as the cells used for immunization. The change of cultivation temperature from 17°C to 25 °C, or vice versa, leads to a gradual replacement of one serotype with another. This transformation of serotypes induced by the change in cultivation temperature was completely reversible, and judging by the immunofluorescence data, occurred in most of, if not in all, the cells. The new serotype appeared and the old one disappeared at the same rate and took 6 to 7 days at 17 °C and 3 to 4 days at 25 °C. In both cases 6 to 8 cell divisions took place during that time.

Stable and unstable transformation by microinjection of macronucleoplasm in Paramecium

Transformation by microinjection of macronucleoplasm in Paramecium caudatum was investigated. Macronucleoplasm with three genetic markers (behavior, trichocyst, and mating type) was injected into the macronucleus. To facilitate microinjection, in most cases, paramecia were immobilized in a gelatin (7.5%) solution. The injected cells began to express a dominant gene (cnrA+ or cnrB+) of the donor 9-24 hr after injection. Expression did not require cell division suggesting injected macronucleoplasm was capable of expressing a phenotype. The amount of injected macronucleoplasm appears to correlate with the frequency of successful expression but not to correlate with the time required for expression. After a number of fissions, the injected cells produced clones which had cells expressing the phenotype of the donor. This suggests that injected macronucleoplasm was replicated and expressed in the recipient cell lines. The transformed clones were classified into two groups. In one group, transformation was stable. All cell lines derived from the injected cells expressed a phenotype similar to the heterozygote of donor and recipient cells. In the other group, transformation was unstable. During the first five to seven fissions after injection, at each division, cells produced one daughter cell which later reverted to the recipient phenotype. After this unstable period, cells no longer produced the recipient phenotype but produced the donor phenotype exclusively. Donor and recipient phenotypes were, thus, segregated in different cell lines. Observation of genetic markers and analysis by computer simulation shed light on the mode of transmission of injected macronucleoplasm. In stable transformation, injected macronucleoplasm appears to be distributed equally to daughter cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic approaches to ciliate pattern formation: from self-assembly to morphogenesis

In the cortex of ciliates, thousands of basal bodies, with their associated cytoskeletal appendages and networks, are arranged in an elaborate pattern whose reproduction at division involves complex morphogenetic movements. Genetic analysis demonstrates that pattern formation relies both on local constraints imposed by the pre-existing organization, and on the differential interpretation of inductive signals by different cell territories whose individual developmental properties are reset at each division.