Localization by indirect immunofluorescence of tetrin, actin, and centrin to the oral apparatus and buccal cavity of the macrostomal form of Tetrahymena vorax

Structure and protein composition of a basal-body scaffold ("cage") in the hypotrich ciliate Euplotes

Cilia on the ventral surface of the hypotrich ciliate Euplotes are clustered into polykinetids or compound ciliary organelles, such as cirri or oral membranelles, used in locomotion and prey capture. A single polykinetid may contain more than 150 individual cilia; these emerge from basal bodies held in a closely spaced array within a scaffold or framework structure that has been referred to as a basal-body "cage". Cage structures were isolated free of cilia and basal bodies; the predominant component of such cages was found on polyacrylamide gels to be a 45-kDa polypeptide. Antisera were raised against this protein band and used for immunolocalizations at the light and electron microscope levels. Indirect immunofluorescence revealed the 45-kDa polypeptide to be localized exclusively to the bases of the ventral polykinetids. Immunogold staining of thin sections of intact cells further localized this reactivity to filaments of a double-layered dense lattice that appears to link adjoining basal bodies into ordered arrays within each polykinetid. Scanning electron microscopy of isolated cages reveals the lower or "basal" cage layer to be a fine lacey meshwork supporting the basal bodies at their proximal ends; adjoining basal bodies are held at their characteristic spacing by filaments of an upper or "medial" cage layer. The isolated cage thus resembles a miniature test-tube rack, able to accommodate varying arrangements of basal-body rows, depending on the particular type of polykinetid. Because of its clear and specific localization to the basal-body cages in Euplotes, we have termed this novel 45-kDa protein "cagein".

Mining the Giardia genome and proteome for conserved and unique basal body proteins

Giardia lamblia is a flagellated protozoan parasite and a major cause of diarrhoea in humans. Its microtubular cytoskeleton mediates trophozoite motility, attachment and cytokinesis, and is characterised by an attachment disk and eight flagella that are each nucleated in a basal body. To date, only 10 giardial basal body proteins have been identified, including universal signalling proteins that are important for regulating mitosis or differentiation. In this study, we have exploited bioinformatics and proteomic approaches to identify new Giardia basal body proteins and confocal microscopy to confirm their localisation in interphase trophozoites. This approach identified 75 homologs of conserved basal body proteins in the genome including 65 not previously known to be associated with Giardia basal bodies. Thirteen proteins were confirmed to co-localise with centrin to the Giardia basal bodies. We also demonstrate that most basal body proteins localise to additional cytoskeletal structures in interphase trophozoites. This might help to explain the roles of the four pairs of flagella and Giardia-specific organelles in motility and differentiation. A deeper understanding of the composition of the Giardia basal bodies will contribute insights into the complex signalling pathways that regulate its unique cytoskeleton and the biological divergence of these conserved organelles.