Glycosomes (protein-glycogen complex) in the canine heart. Ultrastructure, histochemistry and changes induced by acidic treatment

Structure and replication cycle of a virus infecting climate-modulating alga Emiliania huxleyi

The globally distributed marine alga Emiliania huxleyi has cooling effect on the Earth's climate. The population density of E. huxleyi is restricted by Nucleocytoviricota viruses, including E. huxleyi virus 201 (EhV-201). Despite the impact of E. huxleyi viruses on the climate, there is limited information about their structure and replication. Here, we show that the dsDNA genome inside the EhV-201 virion is protected by an inner membrane, capsid, and outer membrane. EhV-201 virions infect E. huxleyi by using fivefold vertices to bind to and fuse the virus' inner membrane with the cell plasma membrane. Progeny virions assemble in the cytoplasm at the surface of endoplasmic reticulum-derived membrane segments. Genome packaging initiates synchronously with the capsid assembly and completes through an aperture in the forming capsid. The genome-filled capsids acquire an outer membrane by budding into intracellular vesicles. EhV-201 infection induces a loss of surface protective layers from E. huxleyi cells, which enables the continuous release of virions by exocytosis.

Cellular Control of Viscosity Counters Changes in Temperature and Energy Availability

Cellular functioning requires the orchestration of thousands of molecular interactions in time and space. Yet most molecules in a cell move by diffusion, which is sensitive to external factors like temperature. How cells sustain complex, diffusion-based systems across wide temperature ranges is unknown. Here, we uncover a mechanism by which budding yeast modulate viscosity in response to temperature and energy availability. This "viscoadaptation" uses regulated synthesis of glycogen and trehalose to vary the viscosity of the cytosol. Viscoadaptation functions as a stress response and a homeostatic mechanism, allowing cells to maintain invariant diffusion across a 20°C temperature range. Perturbations to viscoadaptation affect solubility and phase separation, suggesting that viscoadaptation may have implications for multiple biophysical processes in the cell. Conditions that lower ATP trigger viscoadaptation, linking energy availability to rate regulation of diffusion-controlled processes. Viscoadaptation reveals viscosity to be a tunable property for regulating diffusion-controlled processes in a changing environment.

Molecular cloning and developmental expression of rat glycogenin in cardiac tissue

Glycogenin is a self-glycosylating protein required to initiate glycogen biosynthesis. Utilizing the differential display technique to analyze changes in gene expression during early postnatal cardiac development, we have isolated and cloned a 484 bp cDNA fragment that corresponds to the 3' end of rat glycogenin. Northern blot analysis on neonatal cardiac tissues demonstrated hybridization to a 1.7-1.8 kb transcript, which was highly expressed at 3 days and at progressively reduced levels at 1, 2, 3 and 4 weeks of age. A 1624 bp fragment of rat glycogenin was cloned by RT-PCR that includes a 1002 bp open reading frame encoding a 333 amino acid protein. At the nucleotide level, rat glycogenin exhibited 87.2 and 83.6% identity with human and rabbit glycogenin over the open reading frame. The deduced amino acid sequence showed 86.7 and 83.4% identity with human and rabbit sequences, respectively. Given the significance of glycogenin in glycogen biosynthesis, the results of this study suggest a possible molecular basis for the regulation of glycogen during early postnatal cardiac development. In addition, the nucleotide and amino acid sequences of rat glycogenin may be used to investigate the physiological and pathophysiological roles of glycogenin in rat tissues.

Glycogen accumulations in differentiating mesonephric ducts and tubuli in male human embryos

Human mesonephric duct epithelial cells contained empty appearing regions in the infranuclear cytoplasm when prepared for transmission electron microscopy using glutaraldehyde and osmium fixation. The same regions stained positively with PAS in Epon sections for light microscopy suggesting that glycogen was present. Incubation with saliva abolished the reaction. For electron microscopy the glycogen stained very intensely if a mixture of osmium tetroxide and potassium ferrocyanide was used instead of osmium alone. Glycogen accumulations were present between the ages of 5 to 10 weeks and absent at the age of 15 weeks. Reports by others indicate that glycogen may be present in different reactive forms in relation to its staining behaviour after various fixatives. The present results, and similar studies in other tissues, indicate that osmium tetroxide-potassium ferrocyanide fixative should be used routinely for preservation of embryos and fetuses and where indicated, for ultrastructural identification of glycogen and cytoplasmic filaments in clinical specimens.

Crystalline aggregates of protein-glycogen complexes (alias 'virus-like particles') in skeletal muscle: report of a case and review of the literature

Crystalline arrays of so-called 'virus-like particles' were found in post-mortem samples of skeletal muscle obtained from an 11-month-old female infant. In a large number of skeletal muscle fibres crystalline inclusions were abundant, variously configurated and positively stained with a cytochemical method for polysaccharides. A battery of enzymatic tests, including some with diastase and alpha-amylase, was, however, entirely noncontributory. A muscle biopsy studied 5 months before death had disclosed no crystalline inclusions of any kind. The literature concerning similar cases of 'virus-like particles', crystalline glycogen aggregates or protein-glycogen complexes in muscle is reviewed. Possible reasons underlying the aggregation of protein-glycogen complexes into crystalline arrays are discussed.

Lysosomal glycogen storage mimicking the cytological picture of Pompe's disease as induced in rats by injection of an alpha-glucosidase inhibitor. I. Alterations in liver

The present paper describes an animal model of lysosomal glycogenosis as induced by a competitive inhibitor of alpha-glucosidase. Rats received intraperitoneal injections of the inhibitor, a pseudotetrasaccharide (Acarbose, Bay g 5421); liver tissue was examined by light and electron microscopy. Substrate-histochemical and enzyme-cytochemical methods were used to demonstrate intralysosomal glycogen storage within hepatocytes and Kupffer cells. The cytological picture closely resembled that occurring in glycogenosis type II (Pompe's disease) of humans. After cessation of drug treatment, the glycogen storage was slowly reversible. The present results point to the physiological role of the lysosomal apparatus for intracellular glycogen turnover. On the cellular level, this experimentally induced glycogenosis may be useful as a model of Pompe's disease.