Synthesis and Assembly of the Flagellar Surface1,2

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.

Cortical structure and function in euglenoids with reference to trypanosomes, ciliates, and dinoflagellates

The membrane skeletal complex (cortex) of euglenoids generates and maintains cell form. In this review we summarize structural, biochemical, physiological, and molecular studies on the euglenoid membrane skeleton, focusing specifically on four principal components: the plasma membrane, a submembrane layer (epiplasm), cisternae of the endoplasmic reticulum, and microtubules. The data from euglenoids are compared with findings from representative organisms of three other protist groups: the trypanosomes, ciliates, and dinoflagellates. Although there are significant differences in cell form and phylogenetic affinities among these groups, there are also many similarities in the organization and possibly the function of their cortical components. For example, an epiplasmic (membrane skeletal) layer is widely used for adding strength and rigidity to the cell surface. The ER/alveolus/amphiesmal vesicle may function in calcium storage and regulation, and in mediating assembly of surface plates. GPI-linked variable surface antigens are characteristic of both ciliates and the unrelated trypanosomatids. Microtubules are ubiquitous, and cortices in trypanosomes may relay exclusively on microtubules and microtubule-associated proteins for maintaining cell form. Also, in agreement with previous suggestions, there is an apparent preservation of many cortical structures during cell duplication. In three of the four groups there is convincing evidence that part or all of the parental cortex persists during cytokinesis, thereby producing mosaics or chimeras consisting of both inherited and newly synthesized cortical components.

Evidence for a functional membrane barrier in the transition zone between the flagellum and cell body of Chlamydomonas eugametos gametes

Evidence is presented which supports the concept of a functional membrane barrier in the transition zone at the base of each flagellum of Chlamydomonas eugametos gametes. This makes it unlikely that agglutination factors present on the surface of the cell body can diffuse or be transported to the flagellar membrane. The evidence is as follows: 1) The glycoprotein composition of the flagellar membrane is very different to that of the cell-body plasma membrane. 2) The flagella of gametes treated with cycloheximide, tunicamycin or α, α'-dipyridyl become non-agglutinable but the source of agglutination factors on the cell body is not affected. 3) Even under natural conditions when the flagella are non-agglutinable, for example in vis-à-vis pairs or in appropriate cell strains that are non-agglutinable in the dark, the cell bodies maintain the normal complement of active agglutinins. 4) When flagella of living cells are labeled with antibodies bound to fluorescein, the label does not diffuse onto the cell-body surface. 5) When gametes fuse to form vis-à-vis pairs, the original mating-type-specific antigenicity of each cell body is slowly lost (probably due to the antigens diffusing over both cell bodies), while the specific antigenicity of the flagellar surface is maintained. Even when the flagella of vis-à-vis pairs are regenerated from cell bodies with mixed antigenicity, the antigenicity of the flagella remains matingtype-specific. 6) Evidence is presented for the existence of a pool of agglutination factors within the cell bodies but not on the outer surface of the cells.