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Biomedical subjects

H Spring

Publications and source records attributed to H Spring.

At least 73 records · Page 4Linked to original sources
PubMed1984

Intraosseously transplantable osteosarcoma with regularly disseminating pulmonary metastases in rats.

An intratibially transplantable osteogenic sarcoma in rats, that regularly disseminates osteogenic metastases in the lung, is described. The tumor take rates exceeded 90% 30 days after transplantation. Pulmonary metastases were diagnosed in about 99% of the animals, while metastases in the kidneys (14%), lymph nodes (13%) and liver (3%) occurred less frequently. The mean survival time of untreated animals varied between 36 and 48 days, depending on the age at transplantation. Histologic and scintigraphic findings are reported.

Animals↗
PubMed1982

Nuclear glycogen synthase--fact or artifact?

According to Oron et al. [FEBS Lett. (1980) 118, 255-258], nuclear glycogen synthase represents an artifact of preparation in rat liver nuclei. We investigated the nuclei isolated from in vitro growing HD33 ascites cells with exclusively cytoplasmic, and from in vivo growing HD33 Ehrlich-Lettré ascites tumor cells with mainly intranuclear, glycogen deposition. Biochemical and ultracytochemical analyses revealed the complete absence of any contamination of the isolated nuclei by cytoplasmic glycogen particles and associated glycogen synthase activity. The glycogen synthase residing in isolated nuclei of in vivo growing HD33 ascites tumor cells represents a truly nuclear enzyme activity.

Animals↗
PubMed1981

A nucleolar skeleton of protein filaments demonstrated in amplified nucleoli of Xenopus laevis.

The amplified, extrachromosomal nucleoli of Xenopus oocytes contain a meshwork of approximately 4-nm-thick filaments, which are densely coiled into higher-order fibrils of diameter 30-40 nm and are resistant to treatment with high- and low-salt concentrations, nucleases (DNase I, pancreatic RNase, micrococcal nuclease), sulfhydryl agents, and various nonionic detergents. This filamentous "skeleton" has been prepared from manually isolated nuclear contents and nucleoli as well as from nucleoli isolated by fluorescence-activated particle sorting. The nucleolar skeletons are observed in light and electron microscopy and are characterized by ravels of filaments that are especially densely packed in the nucleolar cortex. DNA as well as RNA are not constituents of this structure, and precursors to ribosomal RNAs are completely removed from the extraction-resistant filaments by treatment with high-salt buffer or RNase. Fractions of isolated nucleolar skeletons show specific enrichment of an acidic major protein of 145,000 mol wt and an apparent pI value of approximately 6.15, accompanied in some preparations by various amounts of minor proteins. The demonstration of this skeletal structure in "free" extrachromosomal nucleoli excludes the problem of contaminations by nonnucleolar material such as perinucleolar heterochromatin normally encountered in studies of nucleoli from somatic cells. It is suggested that this insoluble protein filament complex forms a skeleton specific to the nucleolus proper that is different from other extraction-resistant components of the nucleus such as matrix and lamina and is involved in the spatial organization of the nucleolar chromatin and its transcriptional products.

Animals↗
PubMed1981

Transcriptionally active chromatin in loops of lampbrush chromosomes at physiological salt concentrations as revealed by electron microscopy of sections.

The structural organization of the transcribed loops of lampbrush chromosomes present in the vegetative nuclei of the green algae, Acetabularia mediterranea and A. crenulata, and in oocyte nuclei of the newt, Pleurodeles waltlii, has been studied by electron microscopy of relatively thick (100--200 nm) and ultrathin sections through chromosomes prepared and fixed at physiological salt concentrations. The procedure allows the direct comparison of the same chromosome or chromosome region by light and electron microscopy, that means identification of the transcriptional arrays in specific loops. After such preparations the loop axis reveals regions that are smoothly-contoured ("non-beaded") and only 4 to 7 nm thick and are clearly different from supranucleosomal forms of inactive chromatin fibrils as well as from extended filaments of nucleosomal granules examined in parallel. This indicates that the chromatin of the loops axis of intensely transcribed regions is in a structural form different from that of non-transcribed chromatin. A similarly thin axis has been identified in loops of chromosomes of nuclei fixed in situ. The lateral ribonucleoprotein (RNP) fibrils associated with transcribed loop regions appear as serial arrays of granules, often of regular size, which are smaller in the chromosomes of Acetabularia (mean diameter 18 nm) than in those of amphibia (mean diameter 28 nm). Discontinuous arrays of lateral RNP fibrils and fibril arrays with different polarity are found in some loops. Certain loops and loop regions are characterized by specific patterns of aggregation of such lateral RNP fibrils which appear to correspond to the "granules" visible in these loops in the light microscope. The observations show that arrays of transcriptional complexes in chromosome loops can be visualized in thin sections of material prepared at physiological ionic strength with similar resolution and clarity as in spread preparations of chromosomal material dispersed in extremely low salts buffers. The results are interpreted to approximate the organization of loop structures in vivo and to show that, at physiological ionic strength, the chromatin of the loop axis is organized in a form different from that characteristic of non-transcribed chromatin.

Chlorophyta↗
PubMed1976

Involvement of bristle coat structures in surface membrane formations and membrane interactions during coenocytotomic cleavage in caps of Acetabularia mediterranea.

In the multinucleate cap rays of the green alga Acetabularia mediterranea the cell surface increases dramatically within a short time period during the final stages of coenocytotomic cleavage. In early stages of cyst formation the cytoplast is traversed by numerous large and prolate cleavage vesicles which are characterized by typical columellar or spinous coat structures. The cleavage vesicles are closely associated with the surface of plastids and, to a lesser degree, of mitochondria. This intimate association seems to be mediated by regularly spaced, densely stained intermembranous cross-bridge structures and is maintained throughout cleavage. These cleavage vesicles contain a finely fibrillar material structurally similar to the hyaline layer of mucilage that fills the space between the plasma membrane and cell wall. They line up with invaginations of the plasmalemma and vacuole membranes and, together with smaller vesicles interspersed, constitute preformed "perforation lines" for the final separation of the coenoblast portions. Equidistantly spaced plaques of attachment of such vesicles with surface membrane are described. We hypothesize (a) that the cleavage vesicle membrane is the immediate precursor to the new postcoenocytotomic surface membrane, (b) that the cleavage vesicle coat structures are integrated into the subsurface coat of the plasma membrane, (c) that growth of the laterally attached cleavage vesicles by intussusception of small fuzzy-coated vesicles is confined to their "free ends," (d) that the intermembranous cross-bridge elements are related to bristle coat structures and play a role in the establishment of the cleavage lines, and (e) that the coenocytotomic cleavage process is organized so that adjacent plastids are separated in a way that guarantees the inclusion of several plastids in each cyst.

Acetabularia↗
PubMed1976

Classification of loops of lampbrush chromosomes according to the arrangement of transcriptional complexes.

The arrangement of transcriptional units in the loops of lampbrush chromosomes from oocyte nuclei of urodele amphibia and from primary nuclei of the green alga Acetabularia have been studied in the electron microscope using spread preparations. Loops with different patterns of arrangement of matrix units (i.e. to a first approximation, transcriptional units) can be distinguished: (i) loops consisting of one active transcriptional unit; (ii) loops containing one active transcriptional unit plus additional fibril-free, i.e. apparently untranscribed, intercepts that may include 'spacer' regions; (iii) loops containing two or more transcriptional units arranged in identical or changing polarities, with or without interspersed apparent spacer regions. Morphological details of the transcriptional complexes are described. The observations are not compatible with the concept that one loop reflects one and only one transcriptional unit but, rather, lead to a classification of loop types according to the arrangement of their transcriptional units. We propose that the lampbrush chromosome loop can represent a unit for the coordinate transcription of either one gene or a set of several (different) genes.

Acetabularia↗