Hypervariable polymorphism in the APOC3 gene.
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Alleles↗
Biomedical subjects
J Scott
Publications and source records attributed to J Scott.
Sequence requirements for the editing of apolipoprotein B mRNA.
Apolipoprotein (apo) B48 is produced in the mammalian intestine by a tissue-specific RNA-editing mechanism, which mediates a C to U conversion at position 6666 in apoB mRNA. This generates an inframe translation stop codon (UAA) in place of glutamine (CAA) at position 2153. To establish the sequences required for editing we have used an in vitro conversion assay to monitor the editing of synthetic RNAs by rat intestinal extracts. Transcripts containing 55 nucleotides (positions 6649-6703) or more of human apoB mRNA sequence were edited in vitro. Transcripts containing 42 nucleotides (positions 6648-6689) and 26 nucleotides (positions 6662-6687) were edited at 62 and 24% efficiency, respectively, of the 55-nucleotide sequence. To delineate the precise sequence requirements for editing, mutants were generated where 6-nucleotide sections of the 55-base region were changed to anti-sense sequence. Mutation of the 12-nucleotide region immediately downstream of C-6666 abolished editing, and mutation of 6-base sequences immediately 3' and 5' of this 12-nucleotide region significantly reduced editing. Having identified the key region of interest, a panel of 46 mutant RNAs carrying single base substitutions or deletions between nucleotide positions 6657 and 6685 was constructed. Mutagenesis in the sequence 5'-TGATCAGTATA-3' (positions 6671-6681) downstream of C-6666 had the most dramatic effect, since almost all mutations abolished or greatly reduced conversion in vitro. These results suggest that editing is a highly sequence-specific process. We propose that this downstream region is a recognition and/or binding site for the editing enzyme. A search for this sequence in other genes may help to reveal other RNAs that undergo editing.
Animals↗
Characterization of the apolipoprotein B mRNA editing enzyme: no similarity to the proposed mechanism of RNA editing in kinetoplastid protozoa.
Intestinal apolipoprotein B mRNA is edited at nucleotide 6666 by a C to U transition resulting in a translational stop codon. The enzymatic properties of the editing activity were characterised in vitro using rat enterocyte cytosolic extract. The editing activity has no nucleotide or ion cofactor requirement. It shows substrate saturation with an apparent Km for the RNA substrate of 2.2 nM. The editing enzyme requires no lag period prior to catalysis, and does not assemble into a higher order complex on the RNA substrate. In crude cytosolic extract editing activity is completely abolished by treatment with micrococcal nuclease or RNAse A. Partially purified editing enzyme is no longer sensitive to nucleases, but is inhibited in a dose dependent manner by nuclease inactivated crude extract. The buoyant density of partially purified editing enzyme is 1.3 g/ml, that of pure protein. Therefore, the apolipoprotein B mRNA editing activity consists of a well defined enzyme with no RNA component. The nuclease sensitivity in crude cytosolic extract is explained by the generation of inhibitors for the editing enzyme. The editing of apo B mRNA has little similarity to complex mRNA processing events such as splicing and unlike editing in kinetoplastid protozoa does not utilise guide RNAs.
APOBEC-1 Deaminase↗
Acute heart retransplantation.
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Actuarial Analysis↗
Carboxyl-terminal truncation of apolipoprotein B results in gradual loss of the ability to form buoyant lipoproteins in cultured human and rat liver cell lines.
Apolipoprotein B has an obligatory role in the production of chylomicrons, VLDL, and LDL. Familial hypobetalipoproteinemia is a codominant disorder characterized by reduced levels of apo B containing lipoproteins in plasma. We have previously described mutations of the apo B gene in persons with hypobetalipoproteinemia that predict truncated forms of apo B designated apo B29 (1305 amino acid residues) and apo B39 (1799 residues). Apo B39 was present in the VLDL and LDL fractions of plasma, but apo B29 was not detected in the lipoprotein or infranatant fractions of plasma. Here we have investigated the regions of apo B necessary for apo B containing lipoprotein secretion by expression of constructs designed to express truncated forms of apo B. Apo B13 (583 residues), apo B17 (784 residues), apo B23 (1084 residues), apo B29 (1306 residues), and apo B41 (1880 residues) were transiently expressed in HepG2 cells, and apo B23 and apo B41 were stably expressed in McArdle 7777 cells. Lipoprotein (d less than 1.25 g/mL) and infranatant (d greater than 1.25 g/mL) fractions of conditioned medium were analyzed by immunoprecipitation and SDS-PAGE. The distribution between lipoprotein and infranatant fractions varied: apo B41 was found solely in the lipoprotein fraction; apo B29, apo B23, and apo B17 were present in both fractions, but with stepwise truncation, progressively more apo B was recovered in the infranatant; apo B13 was only in the infranatant. These results demonstrate that deletion from the carboxyl terminal of apo B41 results in a gradual loss of the ability of the truncated proteins to form buoyant lipoprotein particles.
Animals↗
An additional editing site is present in apolipoprotein B mRNA.
Human intestinal apolipoprotein (apo) B mRNA undergoes a C to U RNA editing at nucleotide 6666 to generate a translation stop at codon 2153, which defines the carboxy-terminal of apo B48. Here we show that two of eleven human intestinal cDNAs spanning residue 6666 were edited from a genomically-encoded C to a T at residue 6802 as well as at residue 6666. This additional editing converts Thr (ACA) codon 2198 to Ile (AUA). Synthetic RNA including the nucleotide 6802 was edited in vitro by intestinal extracts at 10-15% of the editing efficiency of nucleotide 6666. A sequence is identified as important for recognition by the editing activity. No secondary structural homology was identified between the two edited sites. No other sequence in the region between 6411 and 6893 nucleotides of apo B mRNA was found to be edited in vivo or in vitro. Apo B RNA editing extracts from intestine did not edit maize cytochrome oxidase II mRNA.
Apolipoproteins B↗
Site-specific creation of uridine from cytidine in apolipoprotein B mRNA editing.
Human apolipoprotein (apo) B mRNA is edited in a tissue specific reaction, to convert glutamine codon 2153 (CAA) to a stop translation codon. The RNA editing product templates and hybridises as uridine, but the chemical nature of this reaction and the physical identity of the product are unknown. After editing in vitro of [32P] labelled RNA, we are able to demonstrate the production of uridine from cytidine; [alpha 32P] cytidine triphosphate incorporated into RNA gave rise to [32P] uridine monophosphate after editing in vitro, hydrolysis with nuclease P1 and thin layer chromatography using two separation systems. By cleaving the RNA into ribonuclease T1 fragments, we show that uridine is produced only at the authentic editing site and is produced in quantities that parallel an independent primer extension assay for editing. We conclude that apo B mRNA editing specifically creates a uridine from a cytidine. These observations are inconsistent with the incorporation of a uridine nucleotide by any polymerase, which would replace the alpha-phosphate and so rule out a model of endonucleolytic excision and repair as the mechanism for the production of uridine. Although transamination and transglycosylation remain to be formally excluded as reaction mechanisms our results argue strongly in favour of the apo B mRNA editing enzyme as a site-specific cytidine deaminase.
Apolipoproteins B↗
A comparative quantitative histological investigation of atrophic changes in the major salivary glands of liquid-fed rats.
Adult male rats were maintained on a wholly liquid diet for 9 days. The three pairs of major glands were removed, weighed, histologically sectioned and examined by stereological and morphometric techniques. The results were compared with the same glands from control rats maintained on normal hard diet and water, and the extent of the differences was compared between the three different types of gland. Up to 50% of the serous acinar volume in the parotid glands, but only 15% in the submandibular glands, was lost after liquid feeding. There was no loss of the mucous acinar tissue in the sublingual gland. Mean acinar diameters were reduced by 33% in parotids and 15% in submandibular glands after liquid feeding, whereas the mucous acini of the sublingual gland remained unaltered. The results point to varying levels of susceptibility to the loss of masticatory reflexes between the parotid serous acini and the submandibular serous acini, and show that the morphology of the sublingual mucous acini is independent of masticatory reflex stimulation. The reductions in acinar diameters suggest that most of the glandular atrophy after liquid feeding is due to acinar cell shrinkage rather than to losses of acinar cell numbers in both parotid and submandibular glands.
Animals↗
The molecular mechanism for the assembly and secretion of ApoB-100-containing lipoproteins.
We have reviewed the literature on the intracellular transport of ApoB-100 and the assembly of the ApoB-100-containing lipoproteins. ApoB-100 is a large molecule (4536 aa) that requires some 15 min to be completed. During the synthesis, the protein could take one of two pathways: a degradational pathway and a pathway that leads to secretion of the protein on mature lipoproteins. The degradational pathway starts with a cotranslational incorporation of ApoB-100 into the membrane of the endoplasmic reticulum in such a way that a relatively large portion of the sequence is exposed on the cytoplasmic surface of this membrane. The membrane bound ApoB-100 is retained in the ER and will eventually undergo intracellular degradation. To enter the pathway that leads to lipoprotein formation, ApoB-100 has to be cotranslationally translocated to the lumen of the ER. ApoB-100 will interact with the lipids during this translation-translocation process and the mature lipoprotein is released into the lumen of the secretory pathway when ApoB-100 is completed and leaves the ribosome. In addition to the mature lipoproteins, the secretory pathway contains an ApoB-100-containing lipoprotein with the density of a HDL particle. This particle is not secreted from the cells but is retained and eventually degraded. Of importance for the retention are sequences present in the C-terminal half of the protein. The mature lipoproteins rapidly leave the ER lumen and are transported to the Golgi apparatus, through which transfer takes considerably longer. The assembly process is a potential site for the regulation of the secretion of the ApoB-100-containing lipoproteins. This process is dependent on active synthesis of phosphatidylcholine and it is also highly dependent on the rate of triacylglycerol synthesis. On the other hand, ApoB-100 appears to be constitutively expressed. An increase in the rate of lipoprotein assembly induced by an increased triacylglycerol synthesis gives rise to an increased recruitment of ApoB-100 nascent polypeptides to interact cotranslationally with lipids. ApoB-100 that is not used for lipoprotein assembly is cotranslationally bound to the ER membrane and sorted to degradation.
Animals↗
Theileria parva: influence of vector, parasite and host relationships on the epidemiology of theileriosis in southern Africa.
The protozoan parasite Theileria parva, transmitted by the ixodid tick Rhipicephalus appendiculatus, is the cause of East Coast fever (ECF) and the related syndromes of Corridor disease and January disease in cattle of eastern, central and southern Africa. It is likely that buffalo (syncerus caffer) are the natural host of T. parva. In eastern and southern Africa, there exists both buffalo-adapted and cattle-adapted T. parva. Disease caused by buffalo-adapted parasites is called Corridor disease, and that caused by cattle-adapted parasites is termed East Coast fever. In eastern Africa, it has been shown experimentally that buffalo-adapted T. parva can, after serial passage in cattle, become adapted to cattle, in which it can then be maintained and cause ECF. This adaptation has been termed transformation. The transformation of buffalo-adapted T. parva to a cattle-adapted parasite has not been reported in southern Africa, and ECF, eradicated from South Africa, Swaziland and southern Mozambique by 1960, has not reappeared in the subcontinent. This paper discusses the possible reasons for this, and hypothesizes that vector population dynamics and the susceptibility of the vector population to infection with T. parva are among the most important factors which influence the expression of ECF as a disease entity, and the likelihood of transformation occurring. It also considers the possibility that disappearance of ECF from southern Africa resulted from the extinction, as a result of vigorous control measures and unfavourable climatic conditions, of non-diapausing populations of R. appendiculatus that may have been introduced from eastern Africa with cattle imported in 1901.
Africa, Southern↗
Test development for the study of physical performance in wrestlers following weight loss.
This study was conducted to develop a testing protocol which would determine the extent of upper-body power output decrements in subjects following weight loss. Five athletes who had trained via upper-body exercise performed a 6-minute variable intensity arm crank test on an isokinetic ergometer before and after a 3-day, 4.5% body weight loss. Blood samples were drawn from a forearm vein pre- and 1, 3, and 5 min post-arm cranking for assessment of lactate, pH, hemoglobin, and hematocrit. The work performed pre-weight loss was significantly (paired t-test, p less than 0.05) greater than that performed post-weight loss. Repeated measures ANOVA yielded no significant differences in blood variables; however, pre-weight loss lactate values were higher and hemoglobin, hematocrit, and pH values were lower than post-weight loss values. It was concluded that a 4.5% body weight reduction resulted in performance decrements during this arm crank test. Survey information obtained from collegiate wrestlers (n = 14) subsequently tested under this protocol indicates the physical demands of this test approximate the physical demands of actual wrestling competition. It would therefore be appropriate to use this protocol during future testing of wrestlers in weight loss studies.
Adult↗
Epidemiology, demography and definitions.
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Antidepressive Agents↗
Prediction, treatment and prognosis of chronic primary major depression.
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Adult↗
Treatment, prediction of relapse and prognosis of chronic primary major depression.
Our study of chronic and non-chronic depressive patients suggests that the following individual factors may predispose a patient to develop chronicity: unipolar depression, neurotic premorbid personality, high familial loading for affective disorder and multiple life events before and after the onset of the illness episode. It is interesting to note that bipolar disorders appear to be under-represented. This may be due to symptomatic chronicity in bipolar illness being more often represented by rapid cycling disorder. Evidence from a group of prospectively ascertained depressives with a median duration of illness of one year showed that apparently 75% of the variance in length of illness episode can be explained. Thus time taken to introduce active treatments, premorbid neuroticism, the occurrence of life events before and after the onset of illness, age at onset of first illness episode and family history of affective disorders were confirmed as important predictor variables. The fact that 85% of patients who develop chronic primary major depressive disorders have previously had an episode of affective illness tends to militate against the stereotype of these patients having a personality disorder. In future, it is important that biological research (for example, neuroendocrine studies) is directed towards chronically depressed patients. In the past, these patients have tended to be excluded from such studies as they represent an atypical population. It is therefore quite clear that future research should be directed towards not only pharmacological but also psychological and social mechanisms which lead to the perpetuation of depressive illness.
Adult↗
GTP and Ca2+ modulate the inositol 1,4,5-trisphosphate-dependent Ca2+ release in streptolysin O-permeabilized bovine adrenal chromaffin cells.
The inositol 1,4,5-trisphosphate (IP3)-induced Ca2+ release was studied using streptolysin O-permeabilized bovine adrenal chromaffin cells. The IP3-induced Ca2+ release was followed by Ca2+ reuptake into intracellular compartments. The IP3-induced Ca2+ release diminished after sequential applications of the same amount of IP3. Addition of 20 microM GTP fully restored the sensitivity to IP3. Guanosine 5'-O-(3-thio)triphosphate (GTP gamma S) could not replace GTP but prevented the action of GTP. The effects of GTP and GTP gamma S were reversible. Neither GTP nor GTP gamma S induced release of Ca2+ in the absence of IP3. The amount of Ca2+ whose release was induced by IP3 depended on the free Ca2+ concentration of the medium. At 0.3 microM free Ca2+, a half-maximal Ca2+ no Ca2+ release was observed with 0.1 microM IP3; at this Ca2+ concentration, higher concentrations of IP3 (0.25 microM) were required to evoke Ca2+ release. At 8 microM free Ca2+, even 0.25 microM IP3 failed to induce release of Ca2+ from the store. The IP3-induced Ca2+ release at constant low (0.2 microM) free Ca2+ concentrations correlated directly with the amount of stored Ca2+. depending on the filling state of the intracellular compartment, 1 mol of IP3 induced release of between 5 and 30 mol of Ca2+.
Adrenal Glands↗
An investigation of parotid gland function and histopathology in autoimmune disease-prone mice of different age groups.
This work aimed to characterize parotid gland function in autoimmune disease-prone murine strains (MRL/n, MRL/l and NZB/W) in relation to increasing age and to relate the extent of functional impairment to the intensity of histopathologic changes observed at the different ages. Pilocarpine-stimulated parotid saliva was collected to assess salivary flow rate and composition. Parotid tissue was then removed for histopathologic assessment. Parotid flow rates were not significantly reduced in autoimmune strains compared to controls but were reduced with age in NZB/W mice and in males of the C57 (control) strain. Age-related salivary compositional changes were present in MRL/l mice and in male NZB/W mice. Focal lymphocytic adenitis increased with age in prevalence and intensity in both sexes. The functional and histopathologic changes were not closely correlated. These results suggest that the parotid gland of autoimmune disease-prone mice provides only a poor replication of the salivary changes in human Sjögren's syndrome. Nevertheless, both the functional and histopathological changes developing in these strains, even though of limited extent, are significantly influenced by age.
Aging↗
Effect of tobacco and alcohol consumption on the Langerhans cell population of human lingual epithelium determined using a monoclonal antibody against HLADR.
Tobacco and alcohol consumption are known predisposing factors to the development of oral cancer, though the mechanism by which they act is unclear. The density of Langerhans cells (LC) has been shown to decrease in the uterine cervix of smokers, possibly indicating reduced immune surveillance and increased risk of malignant change. This study examined biopsies of normal human lateral border of tongue taken from 41 necropsies whose histories of tobacco and alcohol consumption were known. LC were identified in fixed, wax-embedded sections using a monoclonal antibody to HLADR and an immunoperoxidase technique. The mean density of LC in smokers of the equivalent of 11 or more cigarettes daily was significantly higher than moderate and non-smokers when counts were expressed per mm epithelial surface and basement membrane length. There were no significant differences in LC numbers in relation to alcohol consumption, age or sex, but there was a significant interaction between tobacco and alcohol. The results suggest that either human oral LC respond to external toxins, or that physical changes in the epithelial barrier induced by such toxins necessitate the presence of more LC to maintain the integrity of the epithelium.
Adolescent↗
Conjugative transfer genes in staphylococcal isolates from the United States.
Staphylococcus aureus and coagulase-negative staphylococcal isolates from various geographic areas in the United States were examined by using a conjugative transfer gene DNA probe in dot-blot hybridization assays. Of 175 S. aureus isolates, 47 (27%) hybridized with the probe, while 24 of 208 (11.5%) coagulase-negative staphylococci hybridized. However, among methicillin-resistant S. aureus 52% (45 of 89) were probe positive while only 2% (2 of 86) of methicillin-susceptible S. aureus were probe positive. In contrast, 12.5% (22 of 176) of methicillin-resistant and 6% (2 of 32) of methicillin-susceptible coagulase-negative staphylococci contained transfer genes. All but one of the staphylococci containing transfer genes were resistant to gentamicin; 91.5% of S. aureus and 65% of coagulase-negative staphylococci containing transfer genes transferred gentamicin resistance to a S. aureus recipient. Of the 12 isolates that hybridized with the probe but did not transfer resistance, 10 (6 coagulase-negative staphylococci and 4 S. aureus) carried both gentamicin resistance and conjugative transfer genes on the same plasmid. Of these 10, 6 contained plasmid target fragments of sizes different from that of the probe, suggesting additions or deletions of DNA essential for transfer, while in 4 no such alterations could be detected. In two coagulase-negative staphylococci the entire transfer region was apparently integrated into the chromosome. Thus, staphylococci carrying conjugative transfer genes are widely disseminated in the United States and are usually found in multiresistant isolates on plasmids that also encode gentamicin resistance.
Anti-Bacterial Agents↗