Spindle microtubules in the dividing nuclei of trypanosomes.
TL;DR: Preliminary studies indicate that the nuclear division process of trypanosomes is not closely akin to eukaryote mitosis, though it may bear some resemblance to nuclear division in Euglena .
Abstract: Stages in nuclear division have been identified in sections of bloodstream and cultured trypanosomes examined with the electron microscope. In the sleeping sickness trypanosome Trypanosoina rhodesiense at division the nuclear envelope and nucleolus-like endosome persist and become stretched along an axis. An acentric spindle of microtubules encases the elongating endosome As division proceeds the endosomal material fragments In bloodstream forms condensed chromatin (chromosomal material) appears to be associated with the nuclear envelope during the phase of nuclear elongation but to fall away from the envelope late in the phase of nuclear constriction. In culture forms the chromatin is not so abundant The discrete chromosomes envisaged by some light microscopists in stained preparations have not been identified using the electron microscope. The spindle may contain only continuous microtubules. It is suggested that the spindle serves to push the two halves of the nucleus apart, and that the nuclear envelope of each half may act as a vehicle in separation of the daughter genomes. In culture forms of the elasmobranch parasite T. raiae , the endosome appears to disintegrate as the spindle is formed, and from then onwards it becomes difficult to distinguish endosomal material from what might be chromatin. There is no noticeable association between chromatin-like material and the nuclear envelope. Some of the spindle tubules converge on kinetochore-like plaques and the presence of chromosomal microtubules cannot be ruled out. These preliminary studies indicate that the nuclear division process of trypanosomes is not closely akin to eukaryote mitosis, though it may bear some resemblance to nuclear division in Euglena . Within the genus Trypanosoma , moreover, the nuclear division process may vary from species to species and, possibly, even from one strain to another within a species.
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TL;DR: This chapter discusses the characteristics and evolution of mitosis, a types of nuclear division that produce two, or rarely more, daughter nuclei, each containing a chromosome complement approximately similar to that of the original nucleus.
Abstract: Publisher Summary Mitosis is defined as all those types of nuclear division that produce two, or rarely more, daughter nuclei, each containing a chromosome complement approximately similar to that of the original nucleus. The greatest range of variations by which mitosis is accomplished, occurs in the protistan and fungal kingdoms, some members of which are probably most similar to the ancestors of higher plants and animals. The variations in the higher organisms are secondarily derived from the division patterns of typical plants and animals. This chapter discusses the characteristics and evolution of mitosis. The efficiency of mitosis consists of two basic components; the frequency with which each daughter nucleus receives the necessary complete genome complement (genetic efficiency) and the amount of energy and materials expended in the synthesis and operation of the mitotic apparatus. The chapter also discusses the use of mitosis as a phylogenetic marker. It is applicable to all eukaryotic cells and thus is valuable across boundaries where other structures are absent on one side and present in various forms on the other side.
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TL;DR: The current sophistication of available molecular genetic techniques for use in these organisms has allowed a new functional analysis of the cytoskeleton, including functions that are intrinsic to the proliferation and pathogenicity of these parasites.
Abstract: ▪ Abstract Species of the trypanosomatid parasite genera Trypanosoma and Leishmania exhibit a particular range of cell shapes that are defined by their internal cytoskeletons. The cytoskeleton is characterized by a subpellicular corset of microtubules that are cross-linked to each other and to the plasma membrane. Trypanosomatid cells possess an extremely precise organization of microtubules and filaments, with some of their organelles, such as the mitochondria, kinetoplasts, basal bodies, and flagella, present as single copies in each cell. The duplication of these structures and changes in their position during life cycle differentiations provide markers and insight into events involved in determining cell form and division. We have a rapidly increasing catalog of these structures, their molecular cytology, and their ontogeny. The current sophistication of available molecular genetic techniques for use in these organisms has allowed a new functional analysis of the cytoskeleton, including functions that...
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TL;DR: This chapter reviews some aspects of the cell biology of Trypanosoma cruzi, giving emphasis to those aspects related to the ultrastructure of pathogenic protozoa.
Abstract: Publisher Summary Among the protozoa of the Trypanosomatidae family, a large number of species represent agents of diseases, such as Chagas' disease. This chapter reviews some aspects of the cell biology of Trypanosoma cruzi, giving emphasis to those aspects related to the ultrastructure of pathogenic protozoa. Protozoa of the Trypanosomatidae family show, during their, life cycle, several forms which can be easily identified by light microscopy in Giemsa-stained preparations. The chapter also explains the life cycle of T. cruzi. In the life cycle of T. cruzi, there are forms which are able to divide. There is one form, considered to be highly differentiated and responsible for the infectivity of these protozoa, which does not divide. It is highlighted that the trypomastigote form can transform into a rounded form which possesses a free flagellum. This form, which appears in the stomach, is able to transform into either short epimastigotes that start a process of multiplication in the intestinum or into long epimastigotes which move to the more posterior region of the digestive tract of the bug. Cell surface is also emphasized in the chapter.
274 citations
TL;DR: It is concluded that mitosis in yeast is comparable in its general aspect to that observed in typical eukaryotes.
Abstract: Mitosis in yeast Saccharomyces cerevisiae was investigated in thick (0-25-I mum) serial sections with a high voltage electron microscope and in preparations of spheroplasts spread on a water surface. Spindle microtubules originate from a plaque-like structure called the spindle pole bosis the SPB duplicates and a set of long and short microtubules develops on each SPB. The spindle arises as the SPBs separate on the nuclear membrane adense and are not individually visible. Genetic studies, however, have indicated that there are 17 linkage groups. The number of microtubules was determined in diploid and haploid spindles on serial stereo micrographs. In diploid mitosis about 40 microtubules issue from a SPB. Most are non-continuous and often they are visibly associated with a chromatin fibre. The spindle in haploid cells is similar except that the number of microtubules is about half that in diploid cells and the SPB is smaller. The pole-to-pole microtubules vary in number from spindle to spindle, but in each case enough microtubules are present to account for each linkage group being associated with a single non-continuous microtubule. We conclude that mitosis in yeast is comparable in its general aspect to that observed in typical eukaryotes.
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239 citations
TL;DR: The chromosomes of Chinese hamster cells were examined with the electron microscope and the structure and organization of the kinetochore was compared to that of lampbrush chromosomes of certain amphibian oöcytes, dipteran polytene chromosome puffs, and the synaptinemal complex seen during meiotic prophase.
Abstract: The chromosomes of Chinese hamster cells were examined with the electron microscope and the following observations were made concerning the structure and organization of the kinetochore. — The kinetochore consists of a dense core 200–300 A in diameter surrounded hy a less dense zone 200–600 A wide. The dense core consists of a pair of axial fibrils 50–80 A in diameter which may be coiled together in a cohelical manner. The less dense zone about the axial elements is composed of numerous microfibrils which loop out at right angles to the axial fibrils. Together the structures comprise a lampbrush-like filament which extends along the surface of each chromatid. Some sections suggested that two such filaments may be present on each chromatid. The fine structure of kinetochores associated with spindle filaments was essentially the same as those free of filaments. The structure and organization of the kinetochore of these mammalian cells was compared to that of lampbrush chromosomes of certain amphibian oocytes, dipteran polytene chromosome puffs, and the synaptinemal complex seen during meiotic prophase.
235 citations
TL;DR: Ultrastructural and spatial properties of the metaphase kinetochore are examined in various cell types of fetal rats and a method for the direct determination of the thickness of ultrathin sections is described.
201 citations
TL;DR: A diphasic blood agar medium is described which incorporates a number of features from the above media and is less difficult to prepare than Weinman’s (1946) medium which it resembles in several respects.
Abstract: The cultivation of the trypanosomes of the brucei group is generally conceded to be much more difficult than that of the members of the lewisi group. While the latter have been cultivated in a variety of media and have been studied to some extent from the standpoint of their nutritional requirements and metabolic activities (Lwoff, 1940; von Brand, Johnson, and Rees, 1946; Chang, 1948), the cultivation of the former has been less successful, and therefore very little physiological information is available concerning them. Reichenow (1937b) stated that the addition of sugar did not improve his medium for the cultivation of the pathogenic trypanosomes. von Brand and Johnson (1947) found that the respiration of the proventricular form of T. gambiense was sensitive to cyanide. This is in contrast to that of its bloodstream form. Three types of media have given some measure of success in the cultivation of the pathogenic African trypanosomes. On blood agar media they grow either in the water of condensation (Novy and McNeal, 1904; Thomson and Sinton, 1912), or form colonies on the surface of the agar (Weinman, 1946). In liquid media (von Razgha, 1929; Reichenow, 1932, 1934; Brutsaert and Henrard, 1938) they aggregate commonly on the surface of the settled red cells. Slightly more viscous media were developed by Ponselle (1924) and Weinman (1944). They did not indicate where growth occurs in this type of medium. Most investigators use human blood as the blood of choice in the preparation of their media. Those who have used animal blood (Thomson and Sinton, 1912; Reichenow, 1932; Ponselle, 1924; Prates, 1928) did not present data which indicate whether such blood will sustain subcultivation for an indefinite period. In the first section of this paper we describe a diphasic blood agar medium which incorporates a number of features from the above media. It is less difficult to prepare than Weinman’s (1946) medium which it resembles in several respects. The remarkable intensity of sugar consumption by the bloodstream form of the pathogenic African trypanosomes (Yorke, Adams, and Murgatroyd, 1929; von Brand, 1933; Chen and Geiling, 1945; von Brand and Tobie, 1948) suggested the desirability of quantitative studies on sugar utilization by culturestages of these species. The data concerning this point, as well as data on the ammonia production, are summarized in the second section of this paper. 1. CULTURAL OBSERVATIONS Media employed
194 citations
01 Jan 1964
TL;DR: This chapter discusses the protozoan nucleus, which is found in interphasic and in chromosomal resting nuclei of euglenoids and foraminiferans and one frequently encountered type is the karyosome nucleus, characterized by a single centrally located nucleolus.
Abstract: Publisher Summary This chapter discusses the protozoan nucleus. The nuclei of tissue cells of multicellular organisms are of rather uniform appearance. As a rule, chromosomes are not recognizable in them. In contrast, chromocentric nuclei are absent in protozoa. Aside from two exceptions, heterochromatin, including sex chromosomes, is unknown in unicellular organisms. The appearance of resting nuclei in protozoa is determined to a high degree by the variability of the chromosomal material. In protozoa, the chromosomes undergo changes of form and structure in connection with the coiling cycle similar to those of higher organisms. The chromosomes are often quite uncoiled and extended in the interphasic type of resting nuclei and are more or less tightly coiled in the non-interphasic or chromosomal type. the quantity and distribution of the nucleolar material may also be responsible for the appearance of protozoan nuclei. One frequently encountered type is the karyosome nucleus, which is characterized by a single centrally located nucleolus. It is found in interphasic and in chromosomal resting nuclei of euglenoids and foraminiferans.
161 citations