The Permanence of the Infraciliature in Suctoria: An Electronmicroscopic Study of Pattern Formation in Tokophrya infusionum*

SYNOPSIS. The adult Tokophrya infusionum does not possess cilia, but has 20–30 barren basal bodies arranged in 6 short rows adjacent to the contractile vacuole pore. During reproduction, which is by internal budding, the contractile vacuole sinks into the parent along with the invaginating membranes that form the embryo and the wall of the brood pouch. The 6 rows of basal bodies radiate away from the pore and elongate to form 5 long ciliary rows, that encircle the anterior half of the embryo, and 1 short row at the posterior end. The contractile vacuole pore, along with several barren basal bodies, remains in the parent when the embryo is completed. The pore rises to the surface when the embryo is born. New basal bodies are then formed in the parent to replace those which were incorporated into the embryo, and formation of another embryo may begin. The cilia of the embryo are partially resorbed 10 min after the start of metamorphosis, with depolymerization of the ciliary microtubules. Later, the cilia and most of the basal bodies disappear completely, except for a group of barren basal bodies near the embryo's contractile vacuole pore, which form 6 rows and serve as an anlage for the basal bodies and cilia that arise during embryogenesis. There is, therefore, an organized infraciliature in Suctoria throughout their life cycle, and a distinct continuity of basal bodies across the generations.     

Gradients of proliferation of ciliary basal bodies and the determination of the position of the oral primordium in Tetrahymena.

The pattern of proliferation of new basal bodies in ciliary rows (somatic proliferation) in Tetrahymena was observed. Starved and refed cells were used, because proliferation in these cells is more pronounced than that under other circumstances. The formation of new basal bodies is locally determined by the position of "old" pre-existing basal body (short range determination). However, the probability of proliferation associated with any given "old" basal body differs very much. This probability is determined by the spatial coordinates of the particular region of the cell (long range determination); however some randomness in this process was also observed. Two different gradients of proliferation were found. The first gradient is circumferential with a maximum number of new basal bodies added in ciliary rows n, 1, 2 and 3 and the minimum number added in ciliary rows 7, 8 and 9. The second is an antero-posterior gradient with the highest number of new basal bodies added in the midbody region. Moreover, at least in some cases, new oral primordia first appear, as a random proliferation of new basal bodies adjacent to a few old cilia of ciliary row No. 1, resembling somatic proliferation. Then 2,3 or even more clumps of basal bodies appear, each having one old cilium posteriorly. These clumps, however, are not linear groups within the ciliary row but instead they form small fields of basal bodies. These findings suggest, that the same two-gradient system for new basal body addition operates during somatic proliferation and also determines the position of the new oral primordium as the site of the highest gradient value at the intersection of two gradients.     

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”.     

Development of the Ciliary Pattern of the Oral Apparatus of Tetrahymena thermophila1

ABSTRACT. The sequence of formation and ciliation of basal bodies and the subsequent organization of compound ciliary structures of the oral apparatus of Tetrahymena thermophila was reanalyzed with the aid of scanning electron microscopy of cells in which the epiplasmic layer was exposed, as well as by light microscopy of protargol-impregnated specimens. This combination of methods allowed the delineation of numerous steps in the patterning of the oral ciliature, some of which have received little or no previous attention. Highlights include: the initial formation of “strings” of nonciliated new basal bodies in juxtaposition to relatively few basal bodies of the stomatogenic kinety; generation of basal body pairs, roughly oriented along the anteroposterior axis of the cell, that later align side-by-side to assemble promembranelles; condensation and reorientation of promembranelles simultaneous with addition of a third row of basal bodies anterior to the original two rows; production of a very short fourth row of basal bodies at the anterior right end of each developing membranelle; generation of the outer basal body row of the undulating membrane (UM) after alignment of the inner row, with transient ciliation of the inner row preceding permanent ciliation of the outer row; limited basal body resorption at the ends of membranelles; and sculpturing of the right ends of membranelles by a movement of basal bodies associated with formation of the ribbed wall adjacent to the UM. In the old anterior oral apparatus a repetition of the processes of generation of a new outer UM row and sculpturing of right ends of membranelles takes place in synchrony with the corresponding events in the oral primordium, following prior shedding of the old outer UM row and loss of the sculptured pattern in association with temporary regression of the ribbed wall micro-tubules. Oral development is complex, with different processes involved in the assembly of the membranelles and the UM, and with a sequence of distinct events involved in the generation of each of these structures. Speaking comparatively, membranelle development follows the same pathway in many, perhaps all, ciliates in which these structures or their homologues develop from a common stomatogenic field.     

Structural deficiency of 180°-rotated ciliary rows in Tetrahymena: Implications on the inheritance and development of a non-genically acquired cortical trait during vegetative propagation

The present study reveals a deficiency in the number of ciliated basal bodies along 180° rotated ciliary rows (IRs) in Tetrahymena. This feature is common to IRs recently generated in young clones with stable corticotypes (total number of ciliary rows per cell), irrespective of the number of IRs present per cell or their cellular location, and is found before the cell loses any of the IRs. In cells bearing three IRs, the IRs on the two sides of the inversion immediately next to normal ciliary rows (junctures) exhibit an even greater deficiency in ciliated basal bodies, compared to the IR located internally between two other IRs; the normal ciliary rows flanking the inversion are also somewhat deficient. These observations show that the IRs of Tetrahymena are structurally deficient, hence developmentally defective, and suggest that they are intrinsically unstable. We propose that basal body development along IRs tends to be truncated before the stage of ciliation; such basal bodies would fail to acquire the potential to serve as nucleating centers for new basal body development in the next round of basal body proliferation, leading to the eventual loss of the IRs. © 1992 Wiley-Liss, Inc.     

Development of the ciliature of Tetrahymena thermophila: II. Spatial subdivision prior to cytokinesis

The cell surface of Tetrahymena thermophila is made up of an anterior region in which virtually all basal bodies of ciliary rows are ciliated, and the remainder in which ciliated and unciliated basal bodies are fairly irregularly interspersed. This pattern persists through interfission development until the stage of appearance of the equatorial ring of gaps in the ciliary rows that marks the fission zone. The ciliation pattern then becomes subdivided, in large part through the rapid ciliation of contiguous basal bodies located posterior to the fission zone. We interpret this process as a wave of ciliation of preexisting basal bodies that propagates posteriorly from the site of the fission zone. The location, extent, and timing of the ciliation process are the same in inverted as in normally oriented ciliary rows, in spite of the fact that in inverted rows the visible fission zone gap is tardily formed and the local configuration of ciliature around this gap is abnormal. The putative ciliation wave thus does not depend directly upon the local manifestations of the fission zone. However, in a cell-division-arrest mutant, cdaA1, analyzed under conditions in which formation of fission-zone gaps is permanently prevented in some ciliary rows but not in all, it is found that the ciliation pattern becomes subdivided in those ciliary rows that express fission-zone gaps and fails to become subdivided in neighboring rows that fail to manifest gaps. We interpret this combination of findings to indicate that a signal localized at the cell equator initiates a set of polarized developmental events that simultaneously create and demarcate two cellular fields within what was previously one. We further suggest that the characteristic tandem cell division pattern of ciliates is fundamentally a process of segmentation, which might involve mechanisms of gradient subdivision analogous to those taking place during segmentation of insects and other multicellular organisms.     

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.     

Ciliary protein conservation during development in the ciliated protozoan, Oxytricha

The ciliated protozoan Oxytricha fallax possesses multiple highly localized clusters of basal bodies and cilia, all of which are broken down and rebuilt during prefission morphogenesis-with one major exception. The adoral zone of membranelles (AZM) of the ciliate oral apparatus contains approximately 1,500-2,000 basal bodies and cilia, and it is the only compound ciliary structure that is passed morphologically intact to one daughter cell at each cell division. By labeling all proteins in cells, and then picking the one daughter cell possessing the original labeled AZM, we could then evaluate whether or not the ciliary proteins of the AZM were diluted (i.e., either by degradation to constituent amino acids or by subunit exchange) during cell division. Autoradiographic analysis demonstrated that the label was highly conserved in the AZM (i.e., we saw no evidence of turnover), and electrophoretic data illustrate that at least one of the proteins of the AZM is tubulin. We, therefore, conclude that for at least some of the ciliary and basal body proteins of Oxytricha fallax, AZM morphological conservation is essentially equivalent to molecular conservation.     

Organization of actin microfilaments in the apical border of oviduct ciliated cells

Actin microfilaments were localized in quail oviduct ciliated cells using decoration with myosin subfragment S1 and immunogold labeling. These polarized epithelial cells show a well developed cytoskeleton due to the presence of numerous cilia and microvilli at their apical pole. Most S1-decorated microfilaments extend from the microvilli downward towards the upper part of the ciliary striated rootlets with which they are connected. From the microvillous roots, a few microfilaments connect the proximal part of the basal body or the basal foot associated with the basal body. Microfilament polarity is shown by S1 arrowheads pointing away from the microvillous tip to the cell body. Furthermore, short microfilaments are attached to the plasma membrane at the anchoring sites of basal bodies and run along the basal body. The polarity of these short microfilaments is directed from the basal body anchoring fibers downward to the cytoplasm. At the cell periphery, microfilaments from microvillous roots and ciliary apparatus are connected with those of the circumferential actin belt which is associated with the apical zonula adhaerens. Together with the other cytoskeletal elements, the microfilaments increase ciliary anchorage and could be involved in the coordination of ciliary beating. Moreover, microvilli surrounding the cilia probably modify ciliary beating by offering resistance to cilium bending. The presence of microvilli could explain the fact that mainly the upper part of the cilia appanars to be involved in the axonemal bending in metazoan ciliated cells.     

Redistribution of the kinesin-II subunit KAP from cilia to nuclei during the mitotic and ciliogenic cycles in sea urchin embryos

KAP is the non-motor subunit of the heteromeric plus-end directed microtubule (MT) motor protein kinesin-II essential for normal cilia formation. Studies in Chlamydomonas have demonstrated that kinesin-II drives the anterograde intraflagellar transport (IFT) of protein complexes along ciliary axonemes. We used a green fluorescent protein (GFP) chimera of KAP, KAP-GFP, to monitor movements of this kinesin-II subunit in cells of sea urchin blastulae where cilia are retracted and rebuilt with each mitosis. As expected if involved in IFT, KAP-GFP localized to apical cytoplasm, basal bodies, and cilia and became concentrated on basal bodies of newly forming cilia. Surprisingly, after ciliary retraction early in mitosis, KAP-GFP moved into nuclei before nuclear envelope breakdown, was again present in nuclei after nuclear envelope reformation, and only decreased in nuclei as ciliogenesis reinitiated. Nuclear transport of KAP-GFP could be due to a putative nuclear localization signal and nuclear export signals identified in the sea urchin KAP primary sequence. Our observation of a protein involved in IFT being imported into the nucleus after ciliary retraction and again after nuclear envelope reformation suggests KAP115 may serve as a signal to the nucleus to reinitiate cilia formation during sea urchin development.     

Transformation in Tetrahymena thermophila. Development of an inducible phenotype.

Tetrahymena thermophila transforms from a pyriform-shaped trophic form to an elongate rapidly swimming, dispersal form under the appropriate conditions of starvation [Nelsen, E. M., and DeBault, L. E. (1978). J. Protozool.25, 113–119]. The development and control of the dispersal phenotype are examined. After an initial starvation period, the cell replaces its oral structures. During oral replacement, a caudal cilium emerges at the posterior end of the cell. As oral replacement is completed, the cell becomes spindle shaped and the newly-formed oral membranelles are positioned beneath the surface of the cell with somatic ciliary rows exterior to them. The spindle-shaped cell then elongates to become the dispersal form. While the cell is developing the new oral structures, it is also drastically increasing its numbers of somatic basal bodies and cilia. The events in the transformation pathway may be arrested or reversed by feeding the cell, except that once oral replacement has begun, it is completed along with an associated streamlining of the cell. Refed cells revert to the normal vegetative phenotype, except that some shape changes persist for several hours, suggesting that they are compatible with, but independent of, growth. Blockage of protein synthesis with cycloheximide prevents all changes associated with transformation, including the shape changes and elongation of the caudal cilium. The relation between transformation and conjugation has also been examined. Less transformation takes place when mating is possible, but transformed cells may also mate.     

REGULATION OF MICROTUBULES IN TETRAHYMENA : I. Electron Microscopy of Oral Replacement

The coupled resorption and redifferentiation of oral structures which occurs in Tetrahymena pyriformis under conditions of amino acid deprivation has been studied by transmission electron microscopy. Two patterns of ciliary resorption have been found, (a) in situ, and (b) after withdrawal into the cytoplasm. No autophagic vacuoles containing cilia or ciliary axonemes have been seen. Stomatogenic field basal bodies arise by a process of rapid sequential nucleation, with new ones always appearing next to more mature ones, even though the latter may not be fully differentiated. Accessory radial ribbons of microtubules develop immediately adjacent to oral field basal bodies as a late step in their maturation. It can be seen that the formation of basal bodies and their orientation within the oral complex are separate processes. This is true for about 130 of the approximately 170 oral basal bodies; the remaining 40 or so form within the patterned groups of ciliary units as a later event. Clusters of randomly oriented thin-walled microtubules are found surrounding oral basal bodies at all times during stomatogenesis. They may either represent stores of microtubule subunit protein, or serve as effectors of basal body movement during their orientation into pattern.     

Determination of ciliary polarity precedes differentiation in the epithelial cells of quail oviduct.

In quail oviduct epithelium, as in all metazoan and protozoan ciliated cells, cilia beat in a coordinated cycle. They are arranged in a polarized pattern oriented according to the anteroposterior axis of the oviduct and are most likely responsible for transport of the ovum and egg white proteins from the infundibulum toward the uterus. Orientation of ciliary beating is related to that of the basal bodies, indicated by the location of the lateral basal foot, which points in the direction of the active stroke of ciliary beating. This arrangement of the ciliary cortex occurs as the ultimate step in ciliogenesis and following the oviduct development. Cilia first develop in a random orientation and reorient later, simultaneously with the development of the cortical cytoskeleton. In order to know when the final orientation of basal bodies and cilia is determined in the course of oviduct development, microsurgical reversal of a segment of the immature oviduct was performed. Then, after hormone-induced development and ciliogenesis, ciliary orientation was examined in the inverted segment and in normal parts of the ciliated epithelium. In the inverted segment, orientation was reversed, as shown by a video recording of the direction of effective flow produced by beating cilia, by the three-dimensional bending forms of cilia immobilized during the beating cycle and screened by scanning electron microscopy, and by the position of basal body appendages as seen in thin sections by transmission electron microscopy. These results demonstrate that basal body and ciliary orientation are irreversibly determined prior to development by an endogenous signal present early in the cells of the immature oviduct, transmitted to daughter cells during the proliferative phase and expressed at the end of ciliogenesis.     

Bld10/Cep135 stabilizes basal bodies to resist cilia-generated forces

Basal bodies nucleate, anchor, and organize cilia. As the anchor for motile cilia, basal bodies must be resistant to the forces directed toward the cell as a consequence of ciliary beating. The molecules and generalized mechanisms that contribute to the maintenance of basal bodies remain to be discovered. Bld10/Cep135 is a basal body outer cartwheel domain protein that has established roles in the assembly of nascent basal bodies. We find that Bld10 protein first incorporates stably at basal bodies early during new assembly. Bld10 protein continues to accumulate at basal bodies after assembly, and we hypothesize that the full complement of Bld10 is required to stabilize basal bodies. We identify a novel mechanism for Bld10/Cep135 in basal body maintenance so that basal bodies can withstand the forces produced by motile cilia. Bld10 stabilizes basal bodies by promoting the stability of the A- and C-tubules of the basal body triplet microtubules and by properly positioning the triplet microtubule blades. The forces generated by ciliary beating promote basal body disassembly in bld10Δ cells. Thus Bld10/Cep135 acts to maintain the structural integrity of basal bodies against the forces of ciliary beating in addition to its separable role in basal body assembly.     

The fine structure of a cephalic sensory receptor in the copepod Doropygus seclusus Illg (Crustacea: Copepoda: Notodelphyidae)

A cephalic organ of presumed sensory function is described in nauplii and copepodids of the ascidicolous copepod Doropygus seclusus Illg. The receptor, located bilaterally in the anterodorsal head region, is composed of dendrites of extra optic protocerebral origin which have ciliary protrusions with basal bodies, no rootlets, and a basal infrastructure of the 9 + 0 type. The cilia do not branch and their distal terminations contain only one to four microtubules. In nauplii and free-living copepodids, a large epidermal supporting cell encapsulates the end of one dendrite and its cilia in a sac. Other dendrites and their cilia pass through the supporting cell and, terminally, the cilia escape to form a whorled fascicle which contacts the anterolateral cephalic cuticle. The latter end organ reaches its greatest development in the second copepodid stage — the stage which infects the ascidian. All of the symbiotic stages of the copepod have only a proportionately smaller end organ of the saccular type and apparently lack the end organ consisting of whorls of ciliary ends. The function of the receptor is unknown, but it is suggested that the end organ which disappears in the symbiotic stages functions in second copepodids in host recognition.     

Biogenesis of the ciliary roots: participation of the dictyosomes of Golgi's complex.

In this study, the hypothesis of a possible biogenesis of the ciliary roots is suggested, after observing the cilia neurons under the electron microscope, which were found as an exception in the periaqueductal nucleus of the mesencephalon in the domestic cat, conserving the potential to differentiate the cilia, basal bodies and ciliary roots. The dictyosomes of Golgi's complex and Golgi's vesicles participated in this biogenesis. Vesicles of approximately 71.6 nm in diameter had become separated from the periphery of the flattened discoid cisterns of the dictyosome and were aligned normally, in tangential contact with each other, forming rows of vesicles or 'ringed chains', whose points of contact formed the beginning of the 'periodic striation' of a thin ciliary root. Later, the lateral walls of the vesicles and the molecules of the intracisternal proteins gave rise to the interperiodic microfilaments, when the carrier proteins were transformed into structural proteins of the ciliary roots. The parallel apposition of several ringed chains or thin ciliary roots, with their rings joined at the same level (or transversal striations), gave rise to thicker striated roots. This hypothesis of an ultrastructural biogenesis of the striated ciliary roots involves the following six stages: stage I = separation of Golgi's vesicles from the periphery of the flattened disk of dictyosomes near the basal body, with a diameter of over 71.6 nm; stage II = reinforcement of the membrane of the vesicles at the two opposite polar ends of its larger diameter; stage III = alignment of vesicles to form ringed chains, due to the tangential contact between their reinforced points; initiation of the 71.6-nm striation period, roots ringed linearly; stage IV = formation of joining microfilaments between periods (69.2 nm) with the lateral walls of the vesicles and the molecules of the proteins in their content; stage V = lengthening of the thin ciliary roots due to the coupling of new Golgi's vesicles at their ends so that their length increases as a result of the addition of terminal vesicles; stage VI = increase in thickness of the thin ciliary roots, due to the parallel apposition of several ringed chains or thin ringed ciliary roots, at the point where their transversal striation points coincide.     

The formation of basal body domains in the membrane skeleton of Tetrahymena

Differentiated regions within the membrane skeleton are described around basal bodies in the ciliary rows of Tetrahymena. These domains, approximately 1 micron in diameter, are characterized by a relatively dense ultrastructure, the presence of a family of proteins called K antigens (Mr 39-44 x 10(3)) that are recognized by mAb 424A8, and the apparent exclusion of major membrane skeleton proteins that are present in most other regions of the cell (Mr 135, 125 x 10(3]. Mature basal body domains are asymmetric, reflecting the polarity of the cell as a whole. A similar differentiation of the membrane skeleton occurs in the oral apparatus, except here the K antigens surround four clusters of basal bodies (from which this cell takes its name) rather than the individual basal bodies. The development of new basal body domains in the cell cycle is described, with similarities and differences noted between somatic and oral regions of the cell. It is concluded that the capacity of this cell for precise topographic regulation of molecular events in the membrane skeleton makes it a useful model for the study of cortical differentiation in cells generally.     

Cortical morphogenesis in Paramecium: a transcellular wave of protein phosphorylation involved in ciliary rootlet disassembly

In Paramecium, the morphogenesis of the cortex at cell division, which assures reconstruction of shape and surface pattern, has been shown to involve transcellular signals which spread across the cortex like a wave, originating principally from the oral apparatus. One of the events these signals control is the reorganization of the ciliary rootlets through a cycle of regression and regrowth. The ciliary rootlets are nucleated on the ciliary basal bodies and form a scaffold extending over the entire cell surface that is important in aligning the basal bodies and the unit territories organized around them in longitudinal rows. We present evidence that the mechanism underlying their reorganization is cell-cycle-dependent phosphorylation of the structural proteins which compose the ciliary rootlets. We have isolated the rootlets and prepared a polyclonal antibody against them. In situ immunofluorescence of dividing cells with the anti rootlet antibody, and with the monoclonal antibody MPM-2 specific for phosphoproteins shows that a wave of phosphorylation of the ciliary rootlets spreads across the cell at division and just precedes their regression. Two-dimensional Western blot analysis of cytoskeleton and isolated rootlets along with alkaline phosphatase treatment demonstrates that the rootlets are composed of phosphoproteins, while experiments with interphase and dividing cells provide direct evidence that hyperphosphorylation of these proteins at division brings about disassembly of the structure.     

Different functions of tight junctions in the ascidian branchial basket

The stigmatal cells in the branchial basket of ascidians from a number of genera have been examined as to the nature and distribution of their intercellular junctions. The branchial wall consists of ciliated and parietal cells; the ciliated cells are arranged in seven rows and are associated by junctions with other cells in the same row as well as with those in adjacent rows. They are also associated by junctions with peripheral parietal cells. Junctions between adjacent ciliated cells in all cases exhibit tight junctions or zonulae occludentes. However, these cell borders also possess fasciae or zonulae adhaerentes if they are in the same row and the ciliary rootlets insert-into these junctions. If the cells are in adjacent rows they exhibit adhaerentes junctions only in species belonging to the orders Phlebobranchiata and Aplousobranchiata. In contrast, if the cells in adjacent rows belong to the order Stolidobranchiata. they never exhibit any adhaerentes junctions and the ciliary rootlets of the basal bodies from the cilia insert instead into the tight junctions and the non-junctional membrane below them. At the homologous junctional borders between adjacent parietal cells and also at heterologous junctional borders between parietal and ciliated cells, tight junctions alone occur, with no co-existing adhaerentes junctions along their lateral borders. Again, fibrils from ciliary rootlets insert into zonulae occludentes. This shows that tight junctions are capable both of forming permeability barriers, in that they can be seen to prevent the entry of exogenous tracers such as lanthanum, and of acting as adhesive devices.     

The orientation of ciliary basal bodies in quail oviduct is related to the ciliary beating cycle commencement

In mature ciliated cells, the basal feet associated to the basal bodies point out in the direction of the effective stroke of the ciliary beating. In contrast, during ciliogenesis, the basal feet of the newly anchored basal bodies are randomly oriented. The reorientation of basal bodies occurs during the beginning of the coordinated beating cycle of the cilia.