The oral apparatus of Tetrahymena pyriformis, strain WH-6. II. Cytochalasin B inhibition of oral apparatus morphogenesis

An Optimized and Versatile Counter-Flow Centrifugal Elutriation Workflow to Obtain Synchronized Eukaryotic Cells

Cell synchronization is a powerful tool to understand cell cycle events and its regulatory mechanisms. Counter-flow centrifugal elutriation (CCE) is a more generally desirable method to synchronize cells because it does not significantly alter cell behavior and/or cell cycle progression, however, adjusting specific parameters in a cell type/equipment-dependent manner can be challenging. In this paper, we used the unicellular eukaryotic model organism, Tetrahymena thermophila as a testing system for optimizing CCE workflow. Firstly, flow cytometry conditions were identified that reduced nuclei adhesion and improved the assessment of cell cycle stage. We then systematically examined how to achieve the optimal conditions for three critical factors affecting the outcome of CCE, including loading flow rate, collection flow rate and collection volume. Using our optimized workflow, we obtained a large population of highly synchronous G1-phase Tetrahymena as measured by 5-ethynyl-2'-deoxyuridine (EdU) incorporation into nascent DNA strands, bulk DNA content changes by flow cytometry, and cell cycle progression by light microscopy. This detailed protocol can be easily adapted to synchronize other eukaryotic cells.

The actin gene ACT1 is required for phagocytosis, motility, and cell separation of Tetrahymena thermophila

A previously identified Tetrahymena thermophila actin gene (C. G. Cupples and R. E. Pearlman, Proc. Natl. Acad. Sci. USA 83:5160-5164, 1986), here called ACT1, was disrupted by insertion of a neo3 cassette. Cells in which all expressed copies of this gene were disrupted exhibited intermittent and extremely slow motility and severely curtailed phagocytic uptake. Transformation of these cells with inducible genetic constructs that contained a normal ACT1 gene restored motility. Use of an epitope-tagged construct permitted visualization of Act1p in the isolated axonemes of these rescued cells. In ACT1Delta mutant cells, ultrastructural abnormalities of outer doublet microtubules were present in some of the axonemes. Nonetheless, these cells were still able to assemble cilia after deciliation. The nearly paralyzed ACT1Delta cells completed cleavage furrowing normally, but the presumptive daughter cells often failed to separate from one another and later became reintegrated. Clonal analysis revealed that the cell cycle length of the ACT1Delta cells was approximately double that of wild-type controls. Clones could nonetheless be maintained for up to 15 successive fissions, suggesting that the ACT1 gene is not essential for cell viability or growth. Examination of the cell cortex with monoclonal antibodies revealed that whereas elongation of ciliary rows and formation of oral structures were normal, the ciliary rows of reintegrated daughter cells became laterally displaced and sometimes rejoined indiscriminately across the former division furrow. We conclude that Act1p is required in Tetrahymena thermophila primarily for normal ciliary motility and for phagocytosis and secondarily for the final separation of daughter cells.

Profilin Functions in Cytokinesis, Nuclear Positioning, and Stomatogenesis in Tetrahymena thermophila

Expression of the actin-binding protein profilin was disrupted in the ciliate Tetrahymena thermophila by an antisense ribosome method. In cells with the antisense disruption no profilin protein was detected. Cultures of cells with the antisense disruption could be maintained, indicating that profilin was not essential for cytokinesis or vegetative growth. Disruption of the expression of profilin resulted in many cells that were large and abnormally shaped. Formation of multiple micronuclei, which divide mitotically, was observed in cells with a single macronucleus, indicating a defect in early cytokinesis. Some cells with the antisense disruption contained multiple macronuclei, which in Tetrahymena may indicate a function late in cytokinesis. The lack of profilin also affected cytokinesis in the cells that could divide. Normal-sized and normal-shaped cells with the antisense disruption took significantly longer to divide than control cell types. The profilin disruption revealed two new processes in which profilin functions. In cells lacking profilin, micronuclei were not positioned at their normal site on the surface of the macronucleus and phagocytosis was defective. The defect in phagocytosis appeared to be due to disruption of the formation of oral apparatuses (stomatogenesis) and a possible failure in the internalization of phagocytic vacuoles.

Localization of actin in the Tetrahymena basal body-cage complex

In the ciliate cytoskeleton, basal bodies are contained within separate, filamentous cages which are closely associated with basal body microtubules. We have used two polyclonal anti-actin antibodies to localize actin within the basal body-cage complex of Tetrahymena. An antiserum against a Tetrahymena oral apparatus fraction enriched for basal body proteins was produced in rabbits. Agarose-linked chicken muscle actin was used to affinity-purify anti-Tetrahymena actin antibodies from the anti-oral apparatus antiserum. Agarose-linked chicken muscle actin was used to affinity-purify anti-chicken muscle actin antibodies from a commercially available antiserum against chicken muscle actin. Both affinity-purified antibodies were monospecific for Tetrahymena actin on immunoblots containing total oral apparatus protein. The anti-actin antibodies were localized to both somatic and oral basal bodies in Tetrahymena by immunofluorescence microscopy. At the ultrastructural level with the immunogold technique, these antibodies labeled actin epitopes in four distinct regions of the basal body-cage complex: (a) basal body walls, (b) basal plate filaments, (c) proximal-end filaments and (d) cage wall filaments. In addition, the antibody labeled filament bundles that interconnect groups of basal bodies (membranelles) within the oral apparatus. Identical labeling patterns were observed with basal bodies in the isolated oral apparatus, basal bodies in the in situ oral apparatus and somatic basal bodies in situ. Quantitative analysis of gold particle distribution was used to demonstrate the specificity of the antibodies for the basal body-cage complex and to show that non-specific binding of the antibodies was negligible. Preadsorption of the antibody with muscle actin effectively eliminated the capacity of the antibody to bind to proteins on immunoblots and to basal body structures with the immunogold labeling technique. These results provide evidence for actin in the basal body-cage complex and raise the possibility of a contractile system associated with basal bodies.

The oral apparatus of Tetrahymena pyriformis, strain WH-6. IV. Observations on the organization of microtubules and filaments in the isolated oral apparatus and the differential effect of potassium chloride on the stability of oral apparatus microtubules

This report is an ultrastructural analysis of the organization of the isolated oral apparatus of Tetrahymena pyriformis, strain WH-6, syngen 1. Attention has been focused on the organization of microtubules and filaments in oral apparatus membranelles. Oral apparatus membranellar basal bodies were characterized with respect to structural differentiations at the distal and proximal ends. The distal region of membranellar basal bodies contains the basal plate, accessory microtubules and filaments. The proximal end contains a dense material from which emanate accessory microtubules and filaments. There are at least two possibly three different arrangements of accessory structures at the proximal end of membranellar basal bodies. All membranellar basal bodies appear to have a dense material at the proximal end from which filaments emanate. Some of these basal bodies have accessory microtubules and filaments emanating from this dense material. A possible third arrangement is represented by basal bodies which have lateral projections, from the proximal end, of accessory microtubules and filaments which constitute cross or peripheral connectives. There are at least three examples of direct associations between oral apparatus microtubules and filaments: (1) filaments which form links between basal body triplet microtubules, (2) filaments which link the material of the basal plate to internal basal body microtubules, (3) filaments which link together microtubule bundles from membranellar connectives. KCl extraction of the isolated oral apparatus resulted in the selective solubilization of oral apparatus basal bodies, remnants of ciliary axonemes and fused basal plates. Based on their response to KCl extraction two distinct sets of morphologically similar micro tubules can be identified: (a) microtubules which constitute the internal structure of basal bodies and ciliary axonemes, (b) microtubules which constitute the fiber connectives between basal bodies.

The oral apparatus of Tetrahymena pyriformis, strain WH-6. III. The binding of 3H-cytochalasin B by the isolated oral apparatus

The binding of tritium-labelled cytochalasin B by the isolated oral apparatus of Tetrahymena pyriformis, strain WH-6, syngen 1, was investigated. Equilibrium binding studies revealed approximately 1.4 x 10(5) cytochalasin B binding sites per oral apparatus. A Scatchard plot indicates a single class of binding affinities with an association constant of 10(5) liters/mole. Rapid release of oral apparatus-bound cytochalasin B occurred when oral apparatuses were washed and resuspended in 1 mM TRIS without cytochalasin B. Because cytochalasin B binding to oral apparatus microtubular protein was not detected, microtubules are probably not the cytochalasin B binding site. The probable nature of the cytochalasin B binding site within the oral apparatus is discussed.