L'ultrastructure du nucléole de cellules normales et cancéreuses &amp;E.cute;tude au microscope électronique

119

Interphase nucleoli from Vicia faba and Allium cepa meristematic cells are roughly classified into two categories: (a) those that commonly show a rather homogeneous texture (except for small light spaces of various sizes) and frequently contain dense particles 140 A in diameter; (b) those found more frequently in Vicia characterized by a very sharp boundary between a dense outer cortex and a much fighter central core. The dense particles are not found in such nucleoli. In Allium the boundary is more irregular and dense particles are sometimes observed in the outer layer. Many nucleoli show a structure intermediate between these two types. They are characterized by a gradient of increasing density from the center to the periphery and occasionally contain dense 140 A granules.During interphase, certain nucleoli are closely associated with segments of chromatin strands which undoubtedly represent nucleolar organizing regions.The dense 140 A granules are followed during the mitotic cycle. In Allium,

Section: Structure Of the Interphase Nudeolus General Morphologymentioning

confidence: 83%

Section: The Structure Of the Nucleolusmentioning

confidence: 99%

Structure and Mode of Formation of the Nucleolus in Meristematic Cells of Vicia faba and Allium cepa

Lafontaine

1958

119

“…The vermiform internal structure of the nucleolus, first described by Estable and Sotelo (35), and recently studied by electron microscopy (36)(37)(38), has been stated to be Feulgen-positive by Lettr6 and Siebs (39).…”

Section: Discussionmentioning

confidence: 99%

Isolation and Properties of Liver Cell Nucleoli

Monty

Litt

Kay

et al. 1956

1. The significance of the term nucleolus has been discussed. 2. A detailed method for the isolation of nucleoli from already isolated rat or cat liver nuclei has been presented. 3. The presence of DNA in isolated liver cell nucleoli has been indicated by histochemical methods. 4. The percentages of DNA and RNA in the isolated nucleoli have been determined by chemical analysis. 5. The specific activities of aldolase, arginase, and catalase have been determined for two subnuclear fractions and for the isolated nucleoli of rat and cat liver, and the relative amounts of these enzymes in the same subnuclear fractions and nucleoli of rat liver have been measured. 6. The significance of the above findings has been discussed and consideration has been given to what types of isolated nuclei might best serve as starting material for the isolation of nucleoli. 7. A new hypothesis has been presented that nucleoli of the liver cell type may function primarily in furnishing (directly or indirectly) templates for the synthesis of the particular enzymes that must govern the chemistry of mitosis.

“…After it became possible to section tissue suitably for electron microscopy, mammary tumors from agent-bearing mice were found to contain a variety of virus-like particles (7)(8)(9)(10)(11)(12). One variety, measuring about 65 mg in diameter, consisted of a dense shell with a less dense homogeneous interior and was found mostly in the Golgi region of the cytoplasm of ceils (8,10).…”

mentioning

confidence: 99%

“…One variety, measuring about 65 mg in diameter, consisted of a dense shell with a less dense homogeneous interior and was found mostly in the Golgi region of the cytoplasm of ceils (8,10). Another variety consisted of a well defined thin-walled spherical sac with an average diameter of about 100 mg which contained an inner very dense body, centered or excentric, measuring 20 to 35 mg (7)(8)(9)(10)(11)(12). These were found in the intercellular spaces and pictorial evidence suggested that they were formed by a budding process at the cell membrane.…”

mentioning

confidence: 99%

Correlation of Physical and Biological Properties of Mouse Mammary Tumor Agent

Moore

Lasfargues

Murray

et al. 1959

Biophysical procedures have been used to determine the size and structure of the biologically active agent responsible for the transmission, through milk, of mouse mammary adenocarcinoma. Filtration of milk from RIII high-breast-cancer mice through gradocol membranes with decreasing pore sizes indicated that a minimum of activity passed through intermediate pore sizes (100 to 160 m/z). Filtrates through smaller pores were significantly active. Milk treated with small doses of deuteron irradiation produced more tumors than the control, unirradiated milk; larger doses indicated a particle size much less than 100 m/z. Free diffusion experiments indicated that the activity was associated with particles of two different sizes. Altogether the data denoted the presence of a large agent about 100 m# in diameter and a small agent 20 to 30 m/z in diameter or possibly smaller. Furthermore, the presence in the milk of an inhibitor 40 to 60 In# is indicated by the results of all three approaches. The complex nature of the milk agent disclosed by the physical measurements agrees with the picture of one of the structures revealed by electron microscopy as well as with seemingly conflicting measurements reported in the literature. The large agent defined by these indirect methods corresponds to the whole particle seen in the electron microscope and the small agent corresponds to its internal core or nucleoid. It is suggested that the nucleoid is essentially a nucleic acid which may, in the absence of the "inhibitor," retain its activity after being stripped of its outer membrane or sac.