Procentrioles in ciliating and ciliated cells of chick trachea

The development and functions of multiciliated epithelia

Multiciliated cells are epithelial cells that are in contact with bodily fluids and are required for the proper function of major organs including the brain, the respiratory system and the reproductive tracts. Their multiple motile cilia beat unidirectionally to remove particles of external origin from their surface and/or drive cells or fluids into the lumen of the organs. Multiciliated cells in the brain are produced once, almost exclusively during embryonic development, whereas in respiratory tracts and oviducts they regenerate throughout life. In this Review, we provide a cell-to-organ overview of multiciliated cells and highlight recent studies that have greatly increased our understanding of the mechanisms driving the development and function of these cells in vertebrates. We discuss cell fate determination and differentiation of multiciliated cells, and provide a comprehensive account of their locations and functions in mammals.

Centrosome positioning in non-dividing cells

Centrioles and centrosomes are found in almost all eukaryotic cells, where they are important for organising the microtubule cytoskeleton in both dividing and non-dividing cells. The spatial location of centrioles and centrosomes is tightly controlled and, in non-dividing cells, plays an important part in cell migration, ciliogenesis and immune cell functions. Here, we examine some of the ways that centrosomes are connected to other organelles and how this impacts on cilium formation, cell migration and immune cell function in metazoan cells.

Centriole/basal body morphogenesis and migration during ciliogenesis in animal cells

Cilia, either motile or immotile, exist on most cells in the human body. There are several different mechanisms of ciliogenesis, which enable the production of many kinds of cilia and flagella: motile and immotile, transient and long-lived. These can be linked to the cell cycle or associated with differentiation. A primary cilium is extended from a basal body analogous to the mitotic centrioles, whereas the several hundred centrioles needed to form the cilia of a multi-ciliated cell can be generated by centriolar or acentriolar pathways. Little is known about the molecular control of these pathways and most of our knowledge comes from ultrastructural studies. The increasing number of genetic diseases linked to dysfunctional cilia and basal bodies has renewed interest in this area, and recent proteomic and cell biological studies in model organisms have helped to shed light on the molecular components of these enigmatic organelles.

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.

Intracytoplasmic ciliary elements in epidermal cells of Syndesmis echinorum and Paravortex cardii (Platyhelminthes, Dalyellioida)

Epidermal cells of Syndesmis echinorum and Paravortex cardii contain many intracytoplasmic ciliary components: clusters of centrioles disorganized and incomplete short axonemes composed of loosely organized microtubules of irregular lengths, fully formed axonemes though some with fewer than nine doublets, and ciliary rootlets. Furthermore, conspicuous dense granules are found in solitary groups in the cytoplasm. Clusters of dense granules are also closely associated with Golgi complexes and developing axonemal microtubules. Since the dense granules decrease in number as the axonemes increase, it is likely that the granules are involved in the formation of axonemal microtubules. Ciliary elements are especially abundant in epidermal cells of Paravortex cardii embryos, some of them resembling those previously described by several authors in differentiating ciliated cells engaged in centriologenesis and ciliogenesis. Attention has been focused on the relative proportion and position of these elements, as well as the different morphology and several assembling states that they exhibit in epidermal cells of adult S. echinorum and adults and embryos of P. cardii. A functional interpretation of some of the findings is given, which allows us to suggest a sequence of ciliogenetic events that occur in epidermal cells of both species.

Early stages of ciliogenesis in the respiratory epithelium of the nasal cavity of rabbit embryos

Previous studies have shown that ciliogenesis in the epithelial cells of various species exhibits similarities as well as differences. In an attempt to establish whether this process is identical in epithelial cells of a single species, early stages of centriole formation not previously described were encountered. Ciliogenesis was investigated in the respiratory epithelium of the nasal cavity of 18 to 23-day-old rabbit embryos. The appearance of groups of deuterosomes and fibrous granules is followed by the radial formation of procentrioles around the deuterosomes and parent centrioles. The majority of the procentrioles, forming acentriolarly, occur in pairs, with their distal ends facing each other, between the deuterosomes. Subsequent growth of these procentrioles between deuterosomes in a group results in separating the deuterosomes from one another. The deuterosomes, however, still remain interconnected by means of the growing procentrioles. Accordingly, long chains and networks consisting of the above-mentioned structures are formed. After the procentrioles have attained a certain length, the chains and networks split into separate deuterosome-procentriole complexes. During these earlier stages of ciliogenesis fibrous granules are present, however, their function is yet to be determined.

Replication of basal bodies and ciliogenesis in a ciliated epithelium of the lamprey

Replication of basal bodies (centrioles) replication and ciliogenesis were followed in the neck segment of the tubular nephron during stage 3 of metamorphosis in the sea lamprey, Petromyzon marinus L. Procentrioles are formed through both centriolar and acentriolar pathways. In the acentriolar pathway, dense granules, initially formed at or near the Golgi apparatus, become closely associated with all developing procentrioles and may provide precursors required for centriole development. Both cylindrical structures and dense bodies are seen in this region and are likely formed from the coalescence of dense granules. Either dense bodies or mature centrioles become the central element in a generative complex from which procentrioles arise. After maturation of the procentrioles into basal bodies, they migrate to the apical surface of the cell where they align themselves and develop a ciliary axoneme from their distal end. There are fundamental similarities in the mechanism of basal body replication during development of a ciliated epithelium in all vertebrates so far examined.

Morphometric aspects of ciliary distribution and ciliogenesis in human nasal epithelium

Observations of freeze-fracture preparations of human nasal epithelium have provided a unique perspective of the spatial distribution of epithelial cell cilia unattainable by more conventional ultrastructural techniques. The initial stages of ciliogenesis were characterized ultrastructurally in these preparations by differentiation of the lumenal aspect of the epithelial cell membrane prior to the emergence and maturation of new cilia. Morphometric analyses of the resultant electron micrographs indicate that the development of an optimal ciliary population during differentiation of ciliated cells may be integral to the adequate functioning of respiratory mucociliary mechanisms. The frequency with which such ciliogenic structures are observed indicates that ciliogenesis is a common feature of the nasal epithelium and suggests that epithelial cell turnover in the nasal cavities is relatively rapid.

An ultrastructural study of morphogenesis of fibrogranular complex and centriole in ductuli efferentes of Chinese hamster

An ultrastructural study of ciliated epithelial cells in the ductuli efferentes of young and adult hamsters has revealed that these cells possess dense granules, dense granule clusters, dense bodies and fibrogranular complexes as reservoirs or precursors for ciliogenesis. The dense granules are first seen in the centrosomal region. Later, many dense granules and dense granule clusters appear in the apical portion of the epithelial cells where, subsequently, dense bodies are also found. Finally, the fibrogranular complexes are formed in adults. Morphological evidence strongly suggests that cilia are formed from diplosomal centrioles, de novo centrioles, dense body centrioles, and fibrogranular complex centrioles. Ciliogenesis begins in the fourth day after birth and increases rapidly in the fifth day. After the sixth day, cilia appear to be generated mostly from dense bodies and the total ciliogenesis activities gradually decrease as the animal ages.

The spermatozoon of arthropoda. XXX. The multiflagellate spermatozoon in the termite Mastotermes darwiniensis

In this paper the spermatozoon of the termite Mastotermes darwiniensis is described. It is the first example of a multiflagellate sperm cell in animals. The sperm consists of a conical head and 100 flagella. Other remarkable features of this sperm cell are the absence of an acrosome, the presence of centrioles containing doublet microtubules instead of triplets, and the presence of axonemes devoid of central tubules and with doublets bearing only one arm. The flagella are feebly motile.

Mitochondrial derivation of centrioles in some endocrine adenomas

Fine structural studies of various endocrine adenomas indicate that mitochondria may serve as progenitors of centrioles and cilia.

Microtubule protein during ciliogenesis in the mouse oviduct

A colchicine-binding assay and quantitative sodium dodecyl sulfate gel electrophoresis have been used to determine the changes which occur in microtubule protein (tubulin) concentrations in the particulate and soluble fractions of mouse oviduct homogenates during that period of development when centriole formation and cilium formation are at a maximum. When mouse oviducts, at various ages after birth, are homogenized in Tris-sucrose buffer, tubulin concentration is partitioned between the soluble (70%) and particulate (30%) fractions. During the period of most active organelle formation (3-12 days), there is a marked increase in colchicine-binding specific activity, in both the soluble and particulate fractions. Microtubule protein concentration increases from 16 to 24% in the soluble fraction, declining to 14% in the adult. In the particulate fractions, microtubule protein concentration increases from 16 to 27%, leveling off at 16% in the adult. We have concluded from these observations and from electron microscopy that colchicine-binding activity in the particulate fractions is related to the presence of centriole precursors in the pellets of homogenized oviducts from newborn mice. These data further suggest that centriole precursor structures are conveniently packaged aggregates of microtubule protein actively synthesized between 3 and 5 days, and maintained at a maximum during the most active period of organelle assembly.