Temperature-induced modifications in size and pattern of microtubular organelles in a ciliate, Dileptus

Supernumerary microtubules were found in the so-called sensory cilia, in addition to a sensory axoneme. The supernumerary microtubules were not structurally connected to a basal body, but were probably anchored to clusters of dense material inside the ciliary shaft. The frequency of appearance of the supernumerary microtubules was found to be temperature-dependent: the higher the temperature during formation of sensory cilia, the greater was the number of supernumerary microtubules in cross-sections, and the more cross-sections contained them. The possibility is discussed that the formation of the supernumerary microtubules is not due to formation of new nucleating sites inside the cilium. Instead, the microtubules may be remnants of a previously existing axoneme, separated from the basal body during the formation of a sensory cilium. Some of the microtubules of the released axoneme may persist as the supernumerary microtubules, if capped with dense material or some other structure within the ciliary shaft.

Detection of plasma membrane cholesterol by filipin during microvillogenesis and ciliogenesis in quail oviduct.

Using filipin as a probe for the presence of membrane cholesterol, the evolution of cholesterol distribution in the apical plasma membrane was studied during estrogen-induced ciliogenesis in quail oviduct and compared with the distribution of intramembrane particles (IMPs). Ciliary growth is preceded by the first step of microvillus differentiation. Microvilli emerge in membrane domains rich in IMPs and devoid of filipin-cholesterol (f-c) complexes. However growing microvillus membrane shows f-c complexes. During ciliary growth, microvilli lengthen from 0.5 to 2 microns, indicating that the microvillar membrane is not a membrane reservoir for ciliogenesis. During ciliary growth, the characteristic ciliary necklace IMP rows appear progressively at the base of cilia. The first IMP row is organized in a membrane circlet lacking of f-c complexes, whereas the new shaft membrane in the middle of the circlet exhibits numerous complexes. These two different domains of the cilia keep their specificity during ciliary growth. Only the ciliary tip shows fewer complexes than the shaft membrane. The apical membrane of differentiated ciliated cells is thus composed of various domains, the ciliary shaft full of f-c complexes and poor in IMPs, the ciliary necklace is devoid of f-c complexes and rich in IMPs, the microvilli membrane is rich in both IMPs and f-c complexes, and the interciliary membrane is poor in both f-c complexes and IMPs, whereas the undifferentiated cells exhibit an apical membrane in which f-c complexes and IMPs are distributed homogeneously.

Ciliary specializations in mating cells of the ciliate Euplotes crassus

In the ciliate Euplotes crassus, mixed cells of different compatible mating types pass through an induction period before agglutinating with each other by means of cilia in the mating reaction. We examined the ciliary membranes of cells involved in the mating reaction by the freeze-fracture technique and detected at least 5 distinct types of specialization, each indicated by a special congregation of intramembrane particles. Near to the necklace, at the ciliary base, we observed a set of several parallel transverse rows of 10–15 nm particles; a longitudinal row of 12 nm particles appeared more distally from the necklace, preferentially in replicas of intermediate regions of the ciliary shaft. These 3 specializations were common to both mating and vegetative cells. The other 2 appeared as more dynamic specializations found exclusively at least in their patterned organization, in the ciliary membranes of mating cells. Taking on the aspects of rosette-like arrays and patches, respectively, the former were positioned regularly on ciliary membrane bulges (containing an electron-opaque granule) and consisted of 8–9 nm particles; the latter had an elliptic shape and contained up to 50 closely packed 9–10 nm particles.

Patterns of basal body addition in ciliary rows in Tetrahymena.

Most naked basal bodies visualized in protargol stains on the surface of Tetrahymena are new basal bodies which have not yet developed cilia. The rarity of short cilia is explained by the rapid development of the ciliary shaft once it begins to grow. The high frequency of naked basal bodies (about 50 percent) in log cultures indicates that the interval between assembly of the basal body and the initiation of the cilium is long, approximately a full cell cycle. Naked basal bodies are more frequent in the mid and posterior parts of the cell and two or more naked basal bodies may be associated with one ciliated basal body in these regions. Daughter cells produced at division are apparently asymmetric with respect to their endowment of new and old organelles.

THE CILIARY NECKLACE

Cilia, primarily of the lamellibranch gill (Elliptio and Mytilus), have been examined in freeze-etch replicas. Without etching, cross fractures rarely reveal the 9 + 2 pattern, although suggestions of ninefold symmetry are present. In etched preparations, longitudinal fractures through the matrix show a triplet spoke alignment corresponding to the spoke periodicity seen in thin sections. Dynein rows can be visualized along the peripheral microtubules in some preparations. Fracture faces of the ciliary membrane are smooth with few membrane particles, except in the regions adjacent to the basal plate. In the transition region below the plate, a unique particle arrangement, the ciliary necklace, is found. In the Elliptio gill, on fracture face A the necklace is comprised of three well-defined rows or strands of membrane particles that encircle the ciliary shaft. The rows are scalloped and each scallop corresponds to a peripheral doublet microtubule. In thin sections at the level of these particles, a series of champagne-glass structures link the microtubular doublets to the ciliary membrane. The ciliary necklace and this "membrane-microtubule" complex may be involved in energy transduction or the timing of ciliary beat. Comparative studies show that these features are present in all somatic cilia examined including those of the ameboflagellate Tetramitus, sea urchin embryos, rat trachea, and nonmotile cilia of cultured chick embryo fibroblasts. The number of necklace strands differs with each species. The necklace has not been found in rat or sea urchin sperm.

THE EFFECTS OF HIGH HYDROSTATIC PRESSURE ON THE MICROTUBULES OF TETRAHYMENA PYRIFORMIS

Exposure of Tetrahymena pyriformis to 7,500 or 10,000 psi of hydrostatic pressure for 2, 5, or 10 min intervals results in a change in cell shape and ciliary activity. Shape changes occur concurrently with a degradation of longitudinal microtubules in a posterior to anterior direction. High pressure also causes a disruption of ciliary activity. Fine structural analysis reveals a breakdown (presumably microtubule depolymerization) of the central ciliary microtubules. The depolymerization begins at the junction of the central ciliary microtubules with the axosome and progresses distally along the ciliary shaft for a distance of about 0.5 µ.

A Quantitative Analysis of Ciliary Movement by Means of High-Speed Microcinematography

1. An optical arrangement for high-speed microcinematography has been designed so as to record ciliary movement, and the movements of single large abfrontal cilia of Mytilus gill have been photographed at 400-500 frames/sec, with brief exposures of 1/20,000 sec. 2. A quantitative description of the movement of the cilium is presented in terms of the changes of the curvature at various regions of the ciliary shaft and of the change of the basal angle. 3. The principle of the description mentioned above is also applied to the movement of the cilium in media of high viscosities, and some parameters of the movement (duration, amplitude of the basal angle, maximum curvature and propagation velocity of the bending wave) are presented. 4. The resistance experienced by the cilium during its beating has been evaluated under some hydrodynamic assumptions, and the flow induced by the cilium and the bending moment of the ciliary shaft due to the viscous resistance have been calculated over a single beat. 5. The change of the degree of bending of the ciliary shaft (curvature) takes place in advance of the change of the bending moment at the same region in the distal as well as in the proximal regions of the ciliary shaft. This fact indicates that active processes are involved in bending and unbending of the ciliary shaft during its beat.