Centriole Replication Research Articles

Centriole behavior in chloramphenicol-treated eggs of the sand dollar, Dendraster excentricus.

This electron microscope study was undertaken to test the prediction made from an indirect assay method for mitotic centers (centrioles), that chloramphenicol inhibits centriole replication during first cleavage division in the eggs of the sand dollar,Dendraster excentricus. Extensive serial sectioning through both untreated and chloramphenicol-treated eggs, coupled with thorough examination of these sections, has demonstrated that 57% of the untreated eggs and 14% of the chloramphenicol-treated eggs contained paired centrioles at a time when centriole pairs normally exist. This study thus gives direct evidence that chloramphenicol inhibits centriole replication.

Identification of early S phase nuclei by observation of centriole replication in cultured human lymphocytes

Early S phase nuclei of cultured human lymphocytes are identified by the observation of the early stage of centriole replication. In such nuclei, condensed chromatin is seen to cover the entire inner surface of nuclear envelope, except the sites of nuclear pores. When the centriole replication is more advanced, chromatin aggregates are found to be in a state of reduced condensation, the loosened state. The association of inactive condensed chromatin with the nuclear envelope in the early S phase makes it quite unlikely, at least in cultured human lymphocytes, that DNA replication is initiated exclusively at the nuclear membrane. The restriction of DNA synthesis to the nuclear periphery is considered to be characteristic of the terminal S phase where chromatin is almost completely dispersed. The effect of amethopterin, a synchrony inducing agent, upon the nuclear transformation is discussed. It is proposed that the transformation of inactive chromatin from the condensed to loosened and further to dispersed state during S phase is a slow and gradual process.

Physico-chemical properties of an agent that induces parthenogenesis in Rana pipiens eggs.

AbstractAll previous work on artificial parthenogenesis in frog eggs, where parthenogenesis is identified by cleavage and subsequent embryonic development, has involved the introduction of some cellular element. Earlier workers have shown that the cleavage initiating agent (CIA) is found primarily in the particulate fractions of various tissues, whereas this investigation indicates that the active molecules sediment only in the 10,000 g precipitable fraction. Since dialysis against EDTA does not remove activity, non‐specific adsorption to particles would appear to be excluded although the failure of distilled water treatment to remove activity may indicate that the CIA is associated with membranes. The CIA is trypsin‐sensitive, but DNase and RNase resistant, indicating that the molecules are protein in nature. Activity is also removed by incubation with a number of depolymerizing agents, including KI, KCl, and Sarkosyl, indicating that the CIA may be a polymer which must be polymerized to retain activity. The mechanism of action of this protein polymer appears to be that of a trigger since a wide range of concentrations will initiate cleavage. Colchicine gradually removes activity from a preparation while D2O increases activity. Both of these molecules are known to act on the polymerized form of microtubule protein with colchicine decreasing and D2O increasing polymerization. Electrophoresis of protein from five CIA‐containing frog tissues reveals a component common to all of them which migrates with an Rf similar to that of microtubule protein. The 10,000 g pellet from frog brain has significant 3H‐colchicine‐binding activity, and to date only microtubule protein has been shown to bind colchicine. Electron micrographs of 10,000 g pellet material from frog brain show the presence of pieces of microtubules enclosed in membranous vesicles. It is therefore possible that the CIA is microtubular in nature, with short pieces of microtubules perhaps acting as a “seed” for further polymerization. The unfertilized frog egg contains much unpolymerized microtubule protein but apparently lacks the proper template or catalyst to trigger the necessary centriole replication and spindle formation for cleavage; the CIA may fill this role.

Centriole Replication and Nuclear Division in Saprolegnia

SUMMARY: Paired centrioles in the hyphae and young sporangia of Saprolegnia ferax and Dictyuchus sterile were aligned end to end at 180° to each other. At the end of interphase new centrioles were replicated on the proximal end of each parent centriole. Each pair of centrioles was associated with a characteristic region of the nuclear envelope, termed the pocket. As the centriole pairs moved apart the mitotic spindle developed between these pockets. Kineto-chores, initially found at the equator of the spindle, became polarized as the nucleus elongated. A characteristic association between the nuclear envelope and astral microtubules is described and its role in nuclear division discussed. Mitochondria frequently lay along tracts of microtubules. The processes of centriole replication, spindle formation and nuclear division are discussed in relation to reports of the ultrastructure of these processes in other organisms.

Formation of centriole and centriole-like structures during meiosis and mitosis in Labyrinthula sp. (Rhizopodea, Labyrinthulida). An electron-microscope study.

ABSTRACT The fine structure of mitosis in vegetative cells of the marine protist Labyrinthida was found to involve formation of two approximately spherical, electron-dense aggregates (termed protocentrioles) 200–300 nm in diameter. Spindle microtubules were directly attached to the structures. The aggregates contained centrally located cartwheel structures but no microtubular elements in the form of a centriole-like cylinder. In non-sporulating cells the aggregates occurred only during mitosis or possibly in late interphase cells. During meiotic zoosporulation de novo centriole formation was observed. Vegetative spindle cells, which contained no centrioles, procentrioles, or centriolar plaques, aggregated then changed into approximately round or oval presporangia within sori. Two protocentrioles were formed in the cytoplasm a few hundred nanometres from each nucleus. Microtubules, oriented in astral ray patterns, were attached directly to each of the protocentrioles. Following migration to opposite sides of the nucleus, each of the protocentrioles differentiated into two centrioles attached at the cartwheel or proximal ends in a longitudinally continuous orientation. Binary fission of the paired centrioles (termed bicentrioles) and reorientation yielded a diplosome or an approximate orthogonal orientation of the organelles. Each mature centriole consisted of the usual cylinder of 9 triplet microtubular blades with a cartwheel complex at the proximal end consisting of 5 or 6 tiers of cartwheels. Further centriole replication appeared to occur by orthogonal budding from mature centrioles.

Centriole replication during ciliogenesis in the chick tracheal epithelium.

Morphological aspects of centriole replication as displayed in tracheal epithelial cells of 15 to 19-day-old chick embryos during ciliogenesis were examined by electron microscopy. It was found that centriole replication and development take place in a finely fibrous region around the two mature centrioles of the diplosome. Procentrioles in early stages of development are observed in clusters. The core of each cluster is occupied by one or more cylindrical structures which gradually disappear as the procentrioles mature. Some of the procentriolar clusters are attached directly to the walls of the diplosomal centrioles by the cylindrical cores. This observation suggests that all of the clusters may form initially in close association with the diplosomal centrioles.

Development of the ciliary complex and microtubules in the cells of rat subcommissural organ.

The fine structure of the rat subcommissural organs from the late stages of gestation through the postnatal to the adult stages was studied with the electron microscope. Emphasis in this report is placed on the development of the cilium with its affiliated structures. With the progress of cytodifferentiation centrioles originally located in the Golgi region migrate to the cell apex, where each then serves as a basal body to form a cilium which has a 9+2 organization of substructures. Thus, each of the mature subcommissural cells is provided with two cilia of motile type. Satellites first appear on one side of the basal body at about 17 fetal days, rapidly increase in number with age, and finally surround the basal body, forming an elaborate latticework. In the perinatal period microtubules progressively increase in number in the distal cytoplasm, which concurrently elongates and forms a prominent projection in the brain ventricle. Closely associated with the microtubules are large clusters of dense granular masses with an undefined border, which bear a close resemblance to the dense masses appearing in the differentiating cells of respiratory epithelium and having been generally assumed to be the precursor substance for centriole replication. However, the mature subcommissural cells contain no centrioles other than the preexisting pair, each of which has organized a cilium. The dense masses in the subcommissural cells are presumed to be involved in the formation of the cytoplasmic microtubules instead of new centrioles.

An electron microscope study of the process of differentiation during spermatogenesis in the drone honey bee ( Apis mellifera L.) with special reference to centriole replication and elimination

Spermatogenesis in the honey bee (Apis mellifera L.) differs from the process in diploid insects in several ways. The primary spermatocytes in the haploid drone undergo an abortive first meiotic division and, further, an unequal division of the secondary spermatocyte occurs. The result is two spermatids rather than the typical four. Associated with the first meiotic division, a centriole replication process occurs resulting in supernumary centrioles; the latter are eliminated from the cells through cytoplasmic blebs prior to the second meiotic division. During the centriole replication process, several single annulate lamellae appear to be differentiated from pre-existing lamellae of endoplasmic reticulum. An amorphous granular material is observed to surround the replicating centrioles, and it is similar to material located in the pores of the annulate lamellae and nuclear envelope. Because of the specific orientation which the annulate lamellae illustrate relative to the replicating centrioles, it is postulated that they are somehow involved in the accumulation of material utilized in centriole replication. The secondary spermatocyte spindle has associated with it a nuclear “wall” composed of alternate vesicular and compact layers of endoplasmic reticulum. The innermost layer of this wall appears to give rise to the spermatid nuclear envelope. Spermatocytes are interconnected by intercellular bridges throughout the process of spermatogenesis and it is postulated that this syncytium synchronizes the division process. Spermiogenesis in the honey bee is similar to that observed in a number of other insects.

CENTRIOLE REPLICATION

Sperm formation was studied in the fern, Marsilea, and the cycad, Zamia, with particular emphasis on the centrioles. In Marsilea, the mature sperm possesses over 100 flagella, the basal bodies of which have the typical cylindrical structure of centrioles. Earlier observations by light microscopy suggested that these centrioles arise by fragmentation of a body known as the blepharoplast. In the youngest spermatids the blepharoplast is a hollow sphere approximately 0.8 micro in diameter. Its wall consists of closely packed immature centrioles, or procentrioles. The procentrioles are short cylinders which progressively lengthen during differentiation of the spermatid. At the same time they migrate to the surface of the cell, where each of them puts out a flagellum. A blepharoplast is found at each pole of the spindle during the last antheridial mitosis, and two blepharoplasts are found in the cytoplasm before this mitosis. Blepharoplasts are also found in the preceding cell generation, but their ultimate origin is obscure. Before the last mitosis the blepharoplasts are solid, consisting of a cluster of radially arranged tubules which bear some structural similarity to centrioles. In Zamia, similar stages are found during sperm formation, although here the number of flagella on each sperm is close to 20,000 and the blepharoplast measures about 10 micro in diameter. These observations are discussed in relation to theories of centriole replication.

Centriole replication. A study of spermatogenesis in the snail Viviparus.

This paper describes the replication of centrioles during spermatogenesis in the Prosobranch snail, Viviparus malleatus Reeve. Sections for electron microscopy were cut from pieces of testis fixed in OsO(4) and embedded in the polyester resin Vestopal W. Two kinds of spermatocytes are present. These give rise to typical uniflagellate sperm carrying the haploid number of 9 chromosomes, and atypical multiflagellate sperm with only one chromosome. Two centrioles are present in the youngest typical spermatocyte. Each is a hollow cylinder about 160 mmicro in diameter and 330 mmicro long. The wall consists of 9 sets of triplet fibers arranged in a characteristic pattern. Sometime before pachytene an immature centriole, or procentriole as it will be called, appears next to each of the mature centrioles. The procentriole resembles a mature centriole in most respects except length: it is more annular than tubular. The daughter procentriole lies with its axis perpendicular to that of its parent. It presumably grows to full size during the late prophase, although the maturation stages have not been observed with the electron microscope. It is suggested that centrioles possess a constant polarization. The distal end forms the flagellum or other centriole products, while the proximal end represents the procentriole and is concerned with replication. The four centrioles of prophase (two parents and two daughters) are distributed by the two meiotic divisions to the four typical spermatids, in which they function as the basal bodies of the flagella. Atypical spermatocytes at first contain two normal centrioles. Each of these becomes surrounded by a cluster of procentrioles, which progressively elongate during the late prophase. After two aberrant meiotic divisions the centriole clusters give rise to the basal bodies of the multiflagellate sperm. These facts are discussed in the light of the theory, first proposed by Pollister, that the supernumerary centrioles in the atypical cells are derived from the centromeres of degenerating chromosomes.