The zoospore of Schizochytrium aggregatum

Frederick Kazama

doi:10.1139/b80-282

The zoospore of Schizochytrium aggregatum

Canadian Journal of Botany ◽

10.1139/b80-282 ◽

1980 ◽

Vol 58 (23) ◽

pp. 2434-2446 ◽

Cited By ~ 14

Author(s):

Frederick Kazama

Keyword(s):

Root System ◽

Nuclear Membrane ◽

Spore Body ◽

Anterior Flagellum ◽

Osmiophilic Granules

The zoospore ultrastructure of the marine protist Schizochytrium aggregatum was examined in detail. The zoospores of S. aggregatum differed considerably from the zoospores of the presumably closely related marine protist Thraustochytrium. The flagella of S. aggregatum emerged from an erumpent area and followed along shallow grooves on the spore body. The mastigonemes of the anterior flagellum are localized along one-third the circumference of the flagellar shaft. There is a concertina-like structure just distal to the kinetosome terminal plate and osmiophilic granules are present within the kinetosome lumen. Microtubular bundles are associated with the kinetosomes and form a "backbone root" system. Serial reconstructions show that each zoospore contains a single tubular mitochondrion. Closely associated with the mitochondrion is a single microbody which in turn is appressed to the nuclear membrane. The ultrastructural data suggest that Schizochytrium aggregatum can be accommodated among the Fungi.

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The Formation, Structure, Distribution and Frequency of Nuclear Pores

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100066644 ◽

1971 ◽

Vol 29 ◽

pp. 518-519

Author(s):

G. G. Maul

Keyword(s):

Nuclear Pore Complex ◽

Nuclear Membrane ◽

Dynamic Structure ◽

Nuclear Pore ◽

Nuclear Pores ◽

Filter Function ◽

Etching Technique ◽

Selective Filter ◽

Membranous Part

The chromatin of eukaryotic cells is separated from the cytoplasm by a double membrane. One obvious structural specialization of the nuclear membrane is the presence of pores which have been implicated to facilitate the selective nucleocytoplasmic exchange of a variety of large molecules. Thus, the function of nuclear pores has mainly been regarded to be a passive one. Non-membranous diaphragms, radiating fibers, central rings, and other pore-associated structures were thought to play a role in the selective filter function of the nuclear pore complex. Evidence will be presented that suggests that the nuclear pore is a dynamic structure which is non-randomly distributed and can be formed during interphase, and that a close relationship exists between chromatin and the membranous part of the nuclear pore complex.Octagonality of the nuclear pore complex has been confirmed by a variety of techniques. Using the freeze-etching technique, it was possible to show that the membranous part of the pore complex has an eight-sided outline in human melanoma cells in vitro. Fibers which traverse the pore proper at its corners are continuous and indistinguishable from chromatin at the nucleoplasmic side, as seen in conventionally fixed and sectioned material. Chromatin can be seen in octagonal outline if serial sections are analyzed which are parallel but do not include nuclear membranes (Fig. 1). It is concluded that the shape of the pore rim is due to fibrous material traversing the pore, and may not have any functional significance. In many pores one can recognize a central ring with eight fibers radiating to the corners of the pore rim. Such a structural arrangement is also found to connect eight ribosomes at the nuclear membrane.

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A High Resolution Cytochemical Study of Nuclear ATPase in Human Spermatozoa

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100116590 ◽

1975 ◽

Vol 33 ◽

pp. 594-595

Author(s):

A. Sosa ◽

L. Calzada

Keyword(s):

High Resolution ◽

Atpase Activity ◽

Nuclear Membrane ◽

Human Sperm ◽

Sperm Nucleus ◽

Human Spermatozoa ◽

Cytochemical Study ◽

Membrane Bound ◽

Sperm Nuclei ◽

Interchromatin Space

The dependence of nuclear metabolism on the function of the nuclear membrane is not well understood. Whether or not the function of the nuclear membrane is partial or totally responsible of the repressed template activity of human sperm nucleus has not at present been elucidated. One of the membrane-bound enzymatic activities which is concerned with the mechanisms whereby substances are thought to cross cell membranes is adenosintriphosphatase (ATPase). This prompted its characterization and distribution by high resolution photogrammetry on isolated human sperm nuclei. Isolated human spermatozoa nuclei were obtained as previously described. ATPase activity was demonstrated by the method of Wachstein and Meisel modified by Marchesi and Palade. ATPase activity was identified as dense and irregularly distributed granules confined to the internal leaflet of the nuclear membrane. Within the nucleus the appearance of the reaction product occurs as homogenous and dense precipitates in the interchromatin space.

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Lamin B receptor: role on chromatin structure, cellular senescence and possibly aging

Biochemical Journal ◽

10.1042/bcj20200165 ◽

2020 ◽

Vol 477 (14) ◽

pp. 2715-2720

Author(s):

Susana Castro-Obregón

Keyword(s):

Cellular Senescence ◽

Nuclear Membrane ◽

Chromatin Structure ◽

Cholesterol Synthesis ◽

Reductase Activity ◽

Chimeric Protein ◽

Nuclear Lamina ◽

Lamin B ◽

Inner Nuclear Membrane ◽

Lamin B Receptor

The nuclear envelope is composed by an outer nuclear membrane and an inner nuclear membrane, which is underlain by the nuclear lamina that provides the nucleus with mechanical strength for maintaining structure and regulates chromatin organization for modulating gene expression and silencing. A layer of heterochromatin is beneath the nuclear lamina, attached by inner nuclear membrane integral proteins such as Lamin B receptor (LBR). LBR is a chimeric protein, having also a sterol reductase activity with which it contributes to cholesterol synthesis. Lukasova et al. showed that when DNA is damaged by ɣ-radiation in cancer cells, LBR is lost causing chromatin structure changes and promoting cellular senescence. Cellular senescence is characterized by terminal cell cycle arrest and the expression and secretion of various growth factors, cytokines, metalloproteinases, etc., collectively known as senescence-associated secretory phenotype (SASP) that cause chronic inflammation and tumor progression when they persist in the tissue. Therefore, it is fundamental to understand the molecular basis for senescence establishment, maintenance and the regulation of SASP. The work of Lukasova et al. contributed to our understanding of cellular senescence establishment and provided the basis that lead to the further discovery that chromatin changes caused by LBR reduction induce an up-regulated expression of SASP factors. LBR dysfunction has relevance in several diseases and possibly in physiological aging. The potential bifunctional role of LBR on cellular senescence establishment, namely its role in chromatin structure together with its enzymatic activity contributing to cholesterol synthesis, provide a new target to develop potential anti-aging therapies.

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