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At least 1,333 records · Page 74Linked to original sources
PubMed1997

Biogenesis and function of lipolysosomes in developing chick hepatocytes.

Proliferation of lipolysosomes is one of the characteristic aspects of embryonic chick hepatocytes. Formation of lipolysosomes is observed in the well-developed trans-Golgi network, with the highest frequency occurring from 11 to 14 days of incubation. The lipolysosomes usually contain a small and electron-dense lipid inclusion; however, during development, they gradually enlarge with an accompanying reduction in the electron density of the inclusion. Lipolysosomes isolated from neonatal chick liver homogenates were mainly composed of esterified cholesterol and showed considerably high activity of lysosomal enzymes. Moreover, the lipolysosome fraction is clearly shown to be a function of intralysosomal lipolysis via acid lipase. This accumulation of esterified cholesterol within lipolysosomes might be attributed to an excessive uptake and conversion of plasma lipoproteins to lipolysosomes. This concept is supported by the appearance of an abundance of coated pits and both "early" and "late" endosomes. The major components of plasma lipoprotein are low density lipoprotein (LDL) and high density lipoprotein (HDL), the cholesterol-rich lipoproteins, whose cholesterol content increases during the last week of incubation when the lipolysosomes quickly enlarge. Plasma lipoprotein particles are produced in the yolk sac epithelium from yolk very low density lipoprotein (VLDL) and transferred via the vitelline circulation to the chick liver. After hatching, when the supply of nutrients from the yolk sac is terminated, lipolysosomes immediately decrease in size and number. The cholesterol and fatty acids released are useful as an energy source and lipid metabolism in general, especially after hatching. Food intake induces the use of and accelerates the disappearance of lipolysosomes. Instead of lipolysosomes, lipid droplets appear and increase in number and size with concomitant increases of triglyceride concentrations in the liver homogenates, suggesting that lipogenesis has begun in the chick hepatocyte.

Animals↗
PubMed1982

Biogenesis of epithelial cell plasma membranes.

Polarized monolayers of cultured epithelial cells, such as the kidney-derived MDCK cell line, when infected with enveloped viruses, provide a convenient model system for study of the intracellular routes followed by newly synthesized glycoproteins to reach specific domains of the plasma membrane. The polarized nature of the monolayers is reflected in the asymmetric assembly of enveloped viruses, some of which, such as influenza and simian virus 5 (SV5), bud from the apical surfaces of the cells, while others, such as vesicular stomatitis virus (VSV), emerge from the basolateral surfaces. MDCK cells can sustain double infection with viruses of different budding polarity, and within such cells the envelope glycoproteins of the two viruses are synthesized simultaneously and assembled into virions at different sites. Immunoelectron microscopic observations of doubly infected cells show that glycoproteins of influenza and VSV traverse the same Golgi apparatus. This indicates that critical sorting steps must take place during or after passage of the glycoproteins through the organelle. Following passage through the Golgi, the HA glycoprotein accumulates almost exclusively at the apical surface, where the influenza virions assemble. Significant amounts of the G protein, however, are detected on both plasma membranes in singly and doubly infected cells, although VSV virion assembly is limited to basolateral domains. These observations indicate that the site of VSV budding is not exclusively determined by the presence of G polypeptides on a given cell-surface domain. It is possible that other cellular or viral components are responsible for the selection of the appropriate budding domain or that the G protein found on the apical surface must be transferred to the basolateral domain before it becomes competent for assembly.

Animals↗
PubMed1983

Collagen biogenesis and assembly into fibrils as shown by ultrastructural and 3H-proline radioautographic studies on the fibroblasts of the rat food pad.

To examine whether collagen is assembled into fibrils within or outside fibroblasts, the connective tissue of the rat foot pad was investigated by electron microscopy and by radioautography at times varying from 4 min to 3 days after an intravenous injection of 3H-proline. The fibroblasts of the rat food pad are long polarized cells with the nucleus at one end, the Golgi apparatus in the center, and a region with long processes at the other end. This region contains secretory granules and is considered to be the secretory pole of the cell. In the Golgi apparatus the stacks of saccules are separated from rough endoplasmic reticulum (rER) by groups of "intermediate vesicles" including similarly structured tubules which may be over 300 nm long and are referred to as "intermediate tubules." The Golgi saccules exhibit distended portions which differ at the various levels of the stack. On the cis side, the distentions tend to be spherical and contain fine looping threads; in the middle of the stack, they are cylindrical and present distinct straight threads; whereas on the trans side, they are again cylindrical, but the straight threads are grouped in parallel aggregates. Between these cylindrical distentions and the secretory granules, there are transitional forms within which thread aggregates are packaged more and more tightly. Finally, the fibroblasts are associated with two types of collagen fibrils: extracellular ones arranged into large groups between the cells and intracellular ones located within long intracytoplasmic channels. Quantitative radioautography after 3H-proline injection reveals that the number of silver grains per unit area reaches a peak over the rER at 4-10 min, Golgi apparatus at 40 min, secretory granules at 60 min, and extracellular collagen fibrils at 3 h. At no time are intracellular collagen fibrils labeled. Qualitative observations further indicate that spherical Golgi distentions are mainly labeled at 40 min, and cylindrical distentions, at 60 min. In addition, from 20 min to 3 hr, some lysosomal elements are labeled. The biogenetic pathway leading to the formation of collagen fibrils is interpreted as follows.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2004

Cytochrome c oxidase biogenesis in a patient with a mutation in COX10 gene.

We report a cytochrome c oxidase (COX)-deficient patient, clinically affected with Leigh-like disease, with a homozygous mutation in the COX10 start codon. Two-dimensional gel electrophoresis showed a decrease of fully assembled COX without the accumulation of partially assembled COX subcomplexes. Western blot analysis with antibodies directed to COX subunits I, II, and IV showed a decrease of these subunits in this patient compared with control. Overexpression of the COX10 protein in the patient's fibroblasts proved that the detected mutation was indeed the disease cause.

Alkyl and Aryl Transferases↗
PubMed2002

In situ heparin-induced peroxisomal reticulum and biogenesis of peroxisomes in pulmonary intravascular macrophages (PIMs) of caprine lung: an ultrastructural and cytochemical study.

Pulmonary intravascular macrophages (PIMs) contain a unique electron-dense globular surface-coat which is sensitive to heparin treatment, halothane anesthesia, and the digestive effect of lipolytic lipase (LPL), suggesting that the coat is predominantly composed of lipoproteins. In the present study, evidence is presented that heparin, when administered intravenously in goats, potentiated both the translocation of the surface-coat into the vacuolar system and the expansion of the Golgi apparatus. Sequentially, these changes were followed by proliferation of peroxisomes in combination with peroxisomal reticulum (PR), a transient precursor of this organelle. The peroxisomes, as well as PR, reacted positively for catalase after aldehyde fixation and 3,3'-diaminobenzidine (DAB) staining. In addition to their role as phagocytes, the ultrastructural and cytochemical detection of peroxisomes suggests a functional capacity of the PIMs, which may be adaptable to the circulating level of free fatty acids (FAAs).

Animals↗
PubMed2002

Genomic potential hypothesis of evolution: a concept of biogenesis in habitable spaces of the universe.

The new hypothesis of evolution establishes a contiguity of life sciences with cosmology, physics, and chemistry, and provides a basis for the search for life on other planets. Chemistry is the sole driving force of the assembly of life, under the subtle guidance exerted by bonding orbital geometry. That phenomenon leads to multiple origins that function on the same principles but are different to the extent that their nucleic acid core varies. Thus, thoughts about the origins of life and the development of complexity have been transferred from the chance orientation of the past to the realm of atomic structures, which are subject to the laws of thermodynamics and kinetics. Evolution is a legitimate subject of basic science, and the complexity of life will submit to the laws of chemistry and physics as the problem is viewed from a new perspective. The paradigm connects life to the big events that formed every sphere of our living space and that keeps conditions fine-tuned for life to persist, perhaps a billion years or more. The "genomic potential" hypothesis leads to the prediction that life like ours is likely to exist in galaxies that are as distant from the origin of the universe as the Milky Way, and that the habitable zone of our galaxy harbors other living planets as well.

Biological Evolution↗