Nobuo Ohwada

Cell biology of normal and abnormal ciliogenesis in the ciliated epithelium.

Ciliogenesis is divided into four stages: (1) generation of centrioles, (2) migration of duplicated centrioles, (3) formation of the basal body-associated structures, and (4) elongation of cilia. The ultrastructural profile of ciliogenesis is fundamentally the same among various kinds of animal species. In acentriolar centriologenesis, centrioles are generated around deuterosomes by the use of fibrous granules. Components of the centriolar precursor structures, and genes that regulate the differentiation of ciliated cells, have been revealed. Ciliary abnormalities are classified into two categories: specific congenital defects of ciliary structure and acquired nonspecific anomalies of the ciliary apparatus. When ciliogenesis is disturbed, various nonspecific ciliary abnormalities develop in the cell. Inhibition of centriole migration results in the development of intracytoplasmic axonemes, cilia within periciliary sheaths, and intracellular ciliated vacuoles. Swollen cilia and the bulging type of compound cilia are formed during ciliary budding and elongation. Primary cilia can also develop from one of a pair of centrioles. They lack dynein arms and are immobile, but work as a mechanosensor and play a role during morphogenesis of the kidney. Abnormal function or structure of primary cilia results in the development of polycystic kidney disease. The axonemes of primary cilia or monocilia in the embryonic node cells are associated with dynein arms and move vortically. They have a role in determining the left-right (L-R) asymmetry of the fetus. This review also discusses the ciliogenesis of a primary cilium in the cell.

Ciliogenesis and ciliary abnormalities

Cilia are motile processes extending from the basal bodies, playing important roles in the mucociliary clearance in the respiratory tract and the transport of the ovum from the ovary to the uterus in mammals. Ciliogenesis is divided into four stages: (1) duplication of centrioles; (2) migration of centrioles to the apical cell surface to become basal bodies; (3) elongation of cilia containing the axoneme; and (4) formation of accessory structures of basal bodies. The orderly course of ciliogenesis appears to be disturbed by various internal and external factors and, as a result, various unusual forms of the ciliary apparatus develop in the cell. Inhibition of basal body migration results in development of intracytoplasmic axonemes, cilia within periciliary sheaths, and intracellular ciliated cysts. Swollen cilia and the bulging type of compound cilia are formed during ciliary budding and elongation. This review also discusses the origin, composition, and function of the centriolar precursor structures.

The primary cilia of secretory cells in the human oviduct mucosa

The human oviduct is lined with a simple columnar epithelium composed of ciliated cells and secretory cells. Primary cilia or solitary cilia usually extend from the apical surface of the secretory cells. The axoneme of the primary cilia is composed of nine peripheral microtubule doublets (9 + 0 pattern) that lack dynein arms and nexin links. Displacement of peripheral doublets to the central region, which is suggested to be attributable to the lack of nexin links, is one of the distinctive features of oviductal primary cilia. The basal body that extends the primary cilium connects to its paired centriole by the striated connector. The basal body is associated with the accessory structures, such as alar sheets, basal feet, and striated rootlets. Several basal feet project laterally from the basal body. The cap of the basal foot serves as the microtubule organizing center. Several striated rootlets radiate from the basal body toward the nucleus. The basal body, the paired centriole, and the basal body-associated structures are considered to play important roles in the stabilization and fixing of the cilium in the proper position on the apical cell surface.

Development of striated rootlets during ciliogenesis in the human oviduct epithelium

Abstract.Striated rootlets in ciliated cells are conical banded structures composed of longitudinally aligned filaments. The formation of striated rootlets during ciliognesis in the human oviduct epithelium was studied by electron microscopy. Primitive rootlets appeared at the proximal side of basal bodies before or at the same time as ciliary budding. After the formation of several striations, the tip of the rootlets extended deeply toward the interior of the cell and became differentiated into two distinct parts, viz., the proximal conical part connected to the basal body and the distal fibrillar part. The periodicity of the striations in the fibrillar part was 68.5±2.95 nm, about 5 nm longer than that of the conical part (63.9±2.25 nm). The dark band in the striation was thicker in the fibrillar part than in the conical part. Since the fibrillar part was not observed in the mature cilium, this part was considered as being either degraded or changed into the conical part during ciliogenesis.

Ultrastructural and immunohistochemical study of the basal apparatus of solitary cilia in the human oviduct epithelium

The basal apparatus of the solitary cilium is composed of the basal body, an associated centriole and the basal body‐associated structures. To see the connection between the basal body and the centriole, we studied the basal apparatus of solitary cilia in human oviductal secretory cells by electron microscopy and immunohistochemistry. A single centriole was present in the vicinity of the basal body of a solitary cilium. The basal body and the single centriole were interconnected by one or two bundles of thin filaments with a few periodic striations. We have called these bundles the striated connector. The periodicity of striations in the striated connector measured 55 ± 6 nm, about 15 nm shorter than that of striated rootlets. The striated connector was immunolabelled with R67 antibody specific to striated rootlets, indicating that they are composed of common molecule(s). Although the true function of the connector is unknown as yet, it could play an important role for stabilising the basal body in the apical cytoplasm.

Localization of γ–tubulin to the Basal Foot Associated with the Basal Body Extending a Cilium

The human oviduct epithelium primarily consists of ciliated cells and secretory cells. Solitary cilia usually extend from the apical surface of the secretory cells. We investigated the localization of γ-tubulin in the ciliary basal apparatus of both cell types by fluorescence immunohistochemistry and immunoelectron microscopy. In addition to basal bodies, γ-tubulin was identified in the lateral basal foot, especially the basal foot cap. This observation is consistent with previous observations that microtubules radiate from the basal foot and the basal foot serves as the microtubule organizing centre.

Immunohistochemical and electron microscopic observations of stromal cells in the human oviduct mucosa

Stromal cells in the lamina propria of the human oviduct mucosa are unique cells that can differentiate into decidual cells during ectopic pregnancy in the oviduct. The nature of stromal cells is still unknown. In the present study, we investigated human oviductal stromal cells with transmission electron microscopy and immunohistochemistry and revealed that they had ultrastructural features similar to myofibroblasts and expressed alpha-smooth muscle actin, a marker used to identify myofibroblasts. Primary cilia were also one of the characteristic profiles of the stromal cells. These findings showed that the connective tissue-stromal cells in the human oviduct mucosa are myofibroblasts. They are considered to play an important role in the transport of oocytes by bringing about contraction of the mucosal folds.

Identification of a 195 kDa protein in the striated rootlet: its expression in ciliated and ciliogenic cells.

Little is known about the molecular composition of the ciliary rootlet. We raised monoclonal antibodies to a crude preparation of striated rootlets isolated from the human oviduct, and obtained a clone (R4109) that specifically labeled the ciliary rootlets. Rootlets associated with the solitary cilium in secretory cells and fibroblasts were also labeled. R4109 identified a 195-kDa protein by immunoblotting. Ciliogenic cells in the oviduct epithelium of young mice were labeled in the globular and/or granular pattern by R4109 by immunofluorescence microscopy. Immunoelectron microscopy showed that they corresponded to fibrogranular complex and dense granule, respectively. The result demonstrated that the 195-kDa protein is a component common to the striated rootlet and dense granule, and thus suggested that dense granules are involved in the rootlet formation.

Intracytoplasmic Lumina in Human Oviduct Epithelium

Intracytoplasmic lumina (ICL) in human oviduct epithelium were investigated with transmission electron microscopy. ICL were found in 43 out of 60 cases examined. They were ultrastructurally characterized by microvilli lining the lumina, periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP) staining-positive finely granular material in the lumina, and secretory vesicles in the cytoplasm surrounding the lumina. Although ICL were observed at various heights within the epithelium, they were mainly seen in basally located cells that did not face the oviduct lumen. Various stages of formation and development of ICL were observed in the basally located epithelial cells with secretory activities. Primary ICL were originated in the cytoplasm where the secretory granules were aggregated with smooth-surfaced tubular vesicles. Electron microscopic observations after PA-TCH-SP staining revealed that ICL were formed by fusion of the secretory granules with the tubular vesicles. ICL were enlarged into round profiles by further fusion of secretory granules and tubular vesicles, and subsequently opened to the oviduct lumen, or fused to each other to develop into large extracellular cysts within the epithelium.

Ultrastructural Study of the Ciliated Cyst in the Human Uterine Tube Epithelium

Ciliated cysts in the human uterine tube epithelium were investigated with the transmission electron microscope. The cysts were about 3-9 microns in diameter and were provided with many ciliary apparatuses and microvilli. Degenerative changes of these cilia, such as electron-dense round or irregular bodies and amorphous substance, were observed in many cysts, but complete disappearance of ciliary structures was not detected in any ciliated cysts. The ciliated cysts were mostly observed in basal cells and were occasionally found in ciliated cells bordering the tubal lumen. In the basal cells, these cysts distended with the increase in degenerated cilia. Distended ciliated-cyst-containing cells became exposed directly to the tubal lumen. U- or reverse omega-shaped deep indentations of the apical surface of ciliated cells confirmed the opening of ciliated cysts into the lumen. It was suggested that the ciliated cysts result from the premature differentiation of basal cells or disturbed migration of centrioles in ciliogenic cells.