Similar Structural Alterations Research Articles

Control of initiation of ColE1 plasmid replication vy alteration of RNA conformation.

Initiation of ColE1 plasmid replication requires hybridization of the primer transcript (RNA II) to the template DNA at the replication origin. The hybridization is inhibited by binding of another RNA, RNA I, to RNA II. This binding, which occurs in the nonessential region proximal to the 5'-end of RNA II, alters the secondary structure of RNA II even in the region far downstream of the segment where RNA I binds. Similar functional and Structural alterations of RNA II are caused by a single-base change within the nonessential region. By forming an alternative structure, the dispensable region affects folding of a downstream region, and thus participates in the regulation of DNA replication.

Mouse skin damage caused by cytolysin from Vibrio vulnificus and by V. vulnificus infection.

Light and electron microscopy of mouse skin damage caused by intradermal infection with a virulent strain of Vibrio vulnificus and by a single intradermal injection of the cytolytic toxin produced by the bacterium revealed similar structural alterations. The epidermis was intact; however, the infection and toxin produced acute cellulitis characterized by extensive extracellular edema; disorganization of collagen bundles; large accumulations of cell debris and plasma proteins; damaged or necrotic fat cells, capillary endothelial cells, and muscle cells; and mild inflammatory cell infiltration. The virulent strain of V. vulnificus produced a capsule and was resistant to phagocytosis in vivo, whereas a weakly virulent strain of the bacterium did not produce a capsule and was readily phagocytized and digested. Factors that may be important in the pathogenesis of V. vulnificus wound infections include a capsule that inhibits phagocytosis and an extracellular cytolytic toxin that is responsible, at least in part, for the severe tissue damage characteristic of such wound infections.

Control of primer formation for ColE1 plasmid replication: Conformational change of the primer transcript

The ColE1 primer transcript (RNA II) hybridizes to the template DNA near the replication origin. The hybridized RNA II is cleaved by RNAase H to form the primer. Hybridization is inhibited by binding of another RNA, RNA I, to RNA II. This binding alters the secondary structure of RNA II even in the region far downstream of the segment where RNA I binds. Similar functional and structural alterations of RNA II are produced by a single base-change within this segment. However, a region of about 200 nucleotides proximal to the 5′ end of RNA II that includes the segment can be deleted with little effect on primer formation. By forming an alternative structure, the dispensable region affects folding of a downstream region, and thus participates in regulation of primer formation.

Changes in the shape of mitochondria following osmotic stress to the unicellular green alga Chlamydomonas reinhardii.

The effects of various stresses on mitochondrial activity and structure within the unicellular green alga Chlamydomonas reinhardii were investigated using the fluorescent probe rhodamine 123. Within control cells, treatment with rhodamine 123 stained an intense fluorescent network, which was considered to be mitochondrial from the similarity in structure to models of mitochondria reconstructed from serial-section electron microscopy, and because this pattern of staining was abolished following the addition of metabolic inhibitors. Following osmotic shrinkage and rehydration, fragmentation of the mitochondrial network was observed within potentially viable cells. This was reversible within 1 h of resuspension in isotonic medium. Exposure of cells to hypertonic solutions of rapidly permeating compounds did not induce similar structural alterations. These changes in the mitochondria were confirmed by thin-section electron microscopy. In the presence of higher osmolalities of non-permeating compounds, which induce a greater loss of viability, rhodamine 123 stained cells uniformly. Following the osmotic stresses induced by slow rates of freezing and subsequent thawing no fragmentation in mitochondrial staining was observed. These findings demonstrate that shrinkage and rehydration may induce alterations to the structure and function of organelles and may be factors in determining cellular viability following osmotic stress.

Metabolic, circulatory, and structural alterations in the rat brain induced by sustained pentylenetetrazole seizures.

Previous studies have demonstrated that bicuculline-induced seizures of 1-2 h in duration lead to structural, metabolic, and circulatory alterations in the rat brain. Such alterations were observed even though cerebral oxygenation seemed adequate. In the present study, we explored whether pentylenetetrazole, a convulsant which interferes with gamma-aminobutyric acid inhibition by mechanisms other than that of bicuculline, leads to similar structural alterations and to similar cerebral metabolic and circulatory changes. The drug was given to paralyzed and artificially ventilated rats in a dose of 100 mg/kg i.v., and seizures were allowed to continue for 1-120 min. The onset of seizures was accompanied by a small perturbation of cerebral cortical energy state, but sustained changes were confined to decreases in phosphocreatine, glycogen, and glucose and increases in lactate, pyruvate, and cyclic nucleotides. A sustained increase in free fatty acid concentration was observed, with the largest change occurring in arachidonic acid concentration. In the cerebellum, metabolic perturbation was clearly less pronounced, but cyclic nucleotide concentrations rose substantially. Local cerebral blood flow increased in all but two structures (frontal cortex and caudoputamen), but pronounced interstructural changes occurred. Nerve cell changes and astrocytic swelling were observed in the cerebral cortex. There was marked status spongiosus due to edema, which was mainly astrocytic and most prominent in cortical layer 3 and in parts of hippocampus. Nerve cell changes were of two basic types. The type 1 injured neurons, condensed and triangular in shape, were mainly confined to the edematous areas. Many of them had cytoplasmic vacuoles which on electron microscopy proved to be mainly dilated Golgi cisternae or mitochondria. As compared with bicuculline-induced epilepsy such abnormal mitochondria appeared to be more frequent. The type 2 neurons had slit-formed intracytoplasmic and perinuclear vacuoles resulting from dilatation of the endoplasmic reticulum cisternae and the nuclear envelope. The cerebellum looked normal by light microscopy. We conclude that, in the rat, sustained seizure activity induced by pentylenetetrazole is accompanied by alterations in EEG activity, in cerebral metabolism and circulation, and in cell structure similar to those elicited by bicuculline.

Influence of short photoperiods on the ultrastructure of hamster Harderian glands.

A sexual dimorphism of the hamster Harderian gland at the ultrastructural level, has been reported. Castration of males and the administration of testosterone to females are known to alter the male type gland to the female type and vice versa. In this paper we present data that exposure to a short photoperiod (1L:23D) can induce similar structural alterations between the 4th and 10th week of exposure. Changes in the male included reduction in the number of tubular clusters and large vacuoles, while in the female the number of membrane formations decreased with an accompanying appearance of tubular clusters.

Electron microscopic alterations in noradrenaline nerve terminals in vas deferens of the rat following chronic administration of reserpine and chlorpromazine.

The alterations in noradrenaline (NA) nerve terminals in the rat vas deferens following chronic (up to 45 days) administration of reserpine (0.5mg/kg/day) and chlorpromazine (20mg/kg/day) have been investigated at the ultrastructural level. Twenty days after reserpinization small cored vesicles (SCVs) completely disappeared and following that, a synapse-like structure was noted between a NA terminal and a smooth muscle cell. Although no remarkable changes were found in SCVs even after chlorpromazine injections for 45 days, this treatment caused a similar structural alteration to that seen in the reserpinization.

Isolation and characterization of acid phosphatase mutants in Schizosaccharomycespombe

72 mutants defective in the activity of the cell surface glycoprotein acid phosphatase were isolated and characterized. The mutants map in one genetic locus, phol. Many of them exhibit altered cell morphology. This characteristic cosegregates with acid phosphatase deficiency, implying that phol controls the activity of acid phosphatase and concomitantly cell morphology. Phol probably also influences growth rate and agglutination behaviour. By purifying acid phosphatase, two structurally related forms can be detected. One is inactive (form I) and one is the active acid phosphatase (form II). Mutant phol-270 and phol-277 lack the inactive form I. Mutant phol -38 exhibits mainly form I, form II being present only in minor amounts. Two other mutants examined differ only slightly from wildtype in their pattern of active and inactive forms. Tryptic peptide maps of the inactive and active acid phosphatase of the wildtype and the corresponding proteins of mutant phol-304 reveal similar structural alterations for the two mutant proteins. The results show that phol controls the expression of the active and inactive acid phosphatase. We conclude that phol represents the structural gene of the two forms of acid phosphatase.

Corneal endothelium.

Replacement of aqueous humor with air for a 30-minute interval produced distinct morphologic changes in the cells of the corneal endothelium of the rabbit eye. Two basic types of structural changes were noted and were labeled explosions or nonexplosions depending on the percent of cell membrane immediately bounding the involved area that appeared to be intact. The damage was observed and photographically recorded in situ with a modified specular reflection microscope. Neither the required mechanical manipulation of the anterior chamber nor the exchange of saline for aqueous humor produced similar structural alterations in the corneal endothelial cells.

Relation between ultrastructure and viability of frozen-thawed Chinese hamster tissue-culture cells

Electron microscopic examination of Chinese hamster tissue-culture cells showed that freezing and thawing result in structural alterations, the type and magnitude of which depend on the cooling and warming velocities used. Cells suspended in Hanks balanced salt solution and cooled to −196 °C at rates exceeding the survival optimum exhibit different patterns and extents of ultrastructural alterations than do cells cooled or warmed at rates lower than optimum. Even though the addition of 0.4 M dimethyl sulfoxide confers some protection, in terms of survival, it does not prevent structural alterations. The types of alterations, however, differ from those found in cells frozen in Hanks alone. Freeze-thaw treatments producing similar percentages of cell survival do not necessarily cause similar structural alterations, nor is there a simple correlation between structural alterations and survival.