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J E Hesketh

Publications and source records attributed to J E Hesketh.

At least 37 records · Page 2Linked to original sources
PubMed1996

Selenoprotein gene expression during selenium-repletion of selenium-deficient rats.

Selenium repletion of selenium-deficient rats with 20 micrograms selenium / kg body weight as Na2SeO3 was used as a model to investigate the mechanisms that control the distribution of the trace element to specific selenoproteins in liver and thyroid. Cytosolic glutathione peroxidase (cGSHPx), phospholipid hydroperoxide glutathione peroxidase (PHGSHPx), and iodothyronine 5'-deiodinase (IDI) activities were all transiently increased in liver 16 to 32 h after ip injection with selenium. However, only cGSHPx and PHGSHPx activities increased in the thyroid where IDI activity was already increased by selenium deficiency. These responses were owing to synthesis of the seleoproteins on newly synthesised and/or existing mRNAs. The selenoprotein mRNAs in the thyroid gland were increased two- and threefold after the transitory increases in selenoprotein activity. In contrast, there were parallel changes in selenoprotein mRNAs and enzyme activities in the liver, with no prolonged rises in mRNA levels. The organ differences suggest that increased thryotrophin (TSH) concentrations, which are known to induce thyrodial IDI and mRNA, may control the mRNAs for all the thyroidal selenoproteins investigated and be a major mechanism for the preservation of thyroidal selenoproteins when selenium supplies are limited.

Animals↗
PubMed1996

The compartmentalization of protein synthesis: importance of cytoskeleton and role in mRNA targeting.

Following the synthesis of mRNA molecules in eukaryotic cells, the transcripts are processed in the nucleus and subsequently transported through the nuclear membrane into the cytoplasm before being sequestered into polysomes where the information contained in the RNA molecule is translated into an amino acid sequence. Recent evidence suggests that an association of mRNAs with the cytoskeleton might be important in targeting mechanisms and, furthermore, in the transport of mRNA from the nucleus to its correct location in the cytoplasm. Until recently, polysomes have been considered to exist in two classes, namely free or membrane-bound. There is now compelling evidence, however, that ribosomes, in addition to being associated with endoplasmic reticulum membranes, also are associated with components of the cytoskeleton. Thus, a large number of morphological and biochemical studies have shown that mRNA, polysomes and translational factors are associated with cytoskeletal structures. Although the actual nature and significance of the interaction between components of the translational apparatus and the cytoskeleton is not yet understood in detail, it would seem evident that such interactions are important in both the spatial organization and control of protein synthesis. Recent work has shown that a subcellular fraction, enriched in cytoskeletal components, contains polysomes and these (cytoskeletal-bound) polysomes have been shown to contain specific mRNA species. Thus, a population of cytoskeletal-bound polysomes may provide a specialized mechanism for the sorting, targeting and topographical segregation of mRNAs. In this review, current knowledge of the subcellular compartmentalization of mRNAs is discussed.

Animals↗
PubMed1996

A localisation signal in the 3' untranslated region of c-myc mRNA targets c-myc mRNA and beta-globin reporter sequences to the perinuclear cytoplasm and cytoskeletal-bound polysomes.

There is increasing evidence that in mammalian cells some mRNAs are localised to specific parts of the cytoplasm and a proportion of mRNAs and polyribosomes are associated with the cytoskeleton. It has been shown previously that c-myc mRNA is present in the perinuclear cytoplasm and associated with the cytoskeleton, and that this localisation is dependent upon the 3' untranslated region of the mRNA. The present studies show that in transfected fibroblasts the c-myc 3' untranslated region is able to localise beta-globin reporter sequences to the perinuclear cytoplasm. Studies with constructs containing deletions within the 3' untranslated region identify the region between bases 194 and 280 as critical for localisation. Transfection of cells with constructs in which this region is linked to beta-globin sequences showed that it was sufficient to localise the chimaeric transcripts to the perinuclear cytoplasm and to cytoskeletal-bound polyribosomes. Transfection with constructs containing a mutated AUUUA sequence within the 194-280 base region showed that this conserved AUUUA is required for targeting of both c-myc mRNA and a chimaeric transcript of beta-globin transcripts linked to the c-myc 3' untranslated region. The region between bases 194 and 280 did not induce instability of beta-globin transcripts and the AUUUA mutation had little effect upon mRNA stability. We propose that this 86 nt region of the 3' untranslated region contains a localisation signal to target c-myc mRNA so that it is retained on cytoskeletal-bound polysomes in the perinuclear cytoplasm; a conserved AUUUA sequence appears to be a critical part of this signal.

Animals↗
PubMed1995

Tissue-specific regulation of selenoenzyme gene expression during selenium deficiency in rats.

Regulation of synthesis of the selenoenzymes cytosolic glutathione peroxidase (GSH-Px), phospholipid hydroperoxide glutathione peroxidase (PHGSH-Px) and type-1 iodothyronine 5'-deiodinase (5'IDI) was investigated in liver, thyroid and heart of rats fed on diets containing 0.405, 0.104 (Se-adequate), 0.052, 0.024 or 0.003 mg of Se/kg. Severe Se deficiency (0.003 mg of Se/kg) caused almost total loss of GSH-Px activity and mRNA in liver and heart. 5'IDI activity decreased by 95% in liver and its mRNA by 50%; in the thyroid, activity increased by 15% and mRNA by 95%. PHGSH-Px activity was reduced by 75% in the liver and 60% in the heart but mRNA levels were unchanged; in the thyroid, PHGSH-Px activity was unaffected by Se depletion but its mRNA increased by 52%. Thus there is differential regulation of the three mRNAs and subsequent protein synthesis within and between organs, suggesting both that mechanisms exist to channel Se for synthesis of a particular enzyme and that there is tissue-specific regulation of selenoenzyme mRNAs. During Se depletion, the levels of selenoenzyme mRNA did not necessarily parallel the changes in enzyme activity, suggesting a distinct mechanism for regulating mRNA levels. Nuclear run-off assays with isolated liver nuclei showed severe Se deficiency to have no effect on transcription of the three genes, suggesting that there is post-transcriptional control of the three selenoenzymes, probably involving regulation of mRNA stability.

Animals↗
PubMed1995

The temporal and cellular expression of c-fos and c-jun in mechanically stimulated rabbit latissimus dorsi muscle.

The levels of c-fos and c-jun mRNA were measured by reverse transcription PCR in the rabbit latissimus dorsi muscle following three separate training regimes, i.e. passive stretch, 10 Hz electrical stimulation or a combination of the two. Both c-fos and c-jun mRNA expression peaked at around 1 h after imposing stretch and at around 4.5-6 h after the initiation of electrical stimulation. The combined stretch/electrical stimulation regime induced biphasic expression of both c-fos and c-jun mRNA, with peaks coinciding temporally with those for the individual regimes. Immunostaining with anti-Fos and anti-Jun antibodies revealed the accumulation of these proteins in both myofibre and interstitial cell nuclei following passive stretch. In contrast, following electrical stimulation the localization of immunoreactive c-Fos and c-Jun proteins was predominantly in interstitial cell nuclei. c-Fos and c-Jun immunoreactivity was also clearly colocalized in a proportion of myonuclei from stretched muscle. These findings suggest that the rapid induction of c-fos and c-jun is an early event in response to mechanical stretch and might trigger [via activator protein-1 (AP-1) transcriptional factors] events leading to muscle fibre hypertrophy. However, the involvement of AP-1 in inducing the phenotypic changes in muscle fibres as a result of electrical stimulation appears less clear.

Animals↗
PubMed1994

Ribosome distribution in normal and infarcted rat hearts.

Distribution of ribosomes throughout the myocardium of normal and infarcted rat hearts was studied by immunofluorescence and laser confocal scanning microscopy. In addition, sections were labelled with peroxidase or immunogold particles for electron microscopic examination. Ligation of the proximal free left coronary artery produced severe myocardial ischaemia, and after 6 days of ligation most of the left ventricular wall was necrotic and partially replaced by granulation tissue. Immunofluorescence microscopy revealed the presence of ribosomes throughout the non-necrotic myocardium. Some cardiac muscle cells located in subendocardial areas and in the border areas surrounding the infarct were particularly intensely stained. Cells constituting the granulation tissue frequently exhibited strong ribosomal immunostaining. Within longitudinally sectioned cardiac muscle cells, ribosomes were organized in strands oriented along the long axis of the cell as well as in a cross-striated pattern. By double labelling of muscle cells with antibodies against ribosomes and Z-line-associated proteins (desmin or alpha-actinin), it was shown that the cross-striated bands of anti-ribosomal staining coincided with the I-bands along the myofibrils. Immunoelectron microscopy confirmed a wide distribution of ribosomes throughout the intermyofibrillar and subsarcolemmal sarcoplasm, and some labelling was also observed within the I-band. The present results indicate that ribosomes are distributed in a characteristic pattern throughout the sarcoplasm of cardiac muscle cells in association with the myofibrils. Furthermore, it is suggested that within viable cardiac muscle cells located adjacent to the infarct, protein synthesis is increased; this might be an important factor in regional development of compensatory hypertrophy of the surviving cardiac muscle cells.

Animals↗
PubMed1993

GLUT-4 and GLUT-1 glucose transporter expression is differentially regulated by contractile activity in skeletal muscle.

Mammalian skeletal muscle expresses GLUT-4 and GLUT-1 glucose transporters. Here, we have investigated whether GLUT-1 and GLUT-4 expression is regulated in muscle by contractile activity. GLUT-1 mRNA levels were high in skeletal muscle at days 16 and 17 of fetal life and decreased markedly by days 19 and 21. In contrast, GLUT-4 mRNA levels were clearly detectable at day 21 of fetal life, and they increased progressively during postnatal life. The timing data for GLUT-4 induction and GLUT-1 repression suggest that these processes are related to skeletal muscle innervation. GLUT-4 mRNA decreased markedly in adult rat and rabbit tibialis anterior muscle after severage of peroneal nerve. In contrast, GLUT-1 mRNA levels showed a 9-fold increase in rat muscle 3 days after denervation. Direct stimulation of rabbit tibialis anterior muscle with extracellular electrodes protected GLUT-4 mRNA levels against the effect of denervation. This indicates that the repression of GLUT-4 mRNA associated with denervation is due, at least in part, to electrical activity. Increased contractile activity induced for 24 h by indirect electrical stimulation at low frequency caused a marked and specific increase in GLUT-1 mRNA levels in rabbit tibialis anterior muscle. Our results indicate that (a) innervation-dependent basal contractile activity regulates in an inverse manner the expression of GLUT-1 and GLUT-4 in skeletal muscle, and (b) enhanced contractile activity stimulates GLUT-1 expression in the absence of modifications to GLUT-4 expression. This suggests the existence of different factors which depend on contractile activity and which control GLUT-1 and GLUT-4 glucose transporter expression in skeletal muscle.

Animals↗
PubMed1993

Clenbuterol mimics effects of innervation on myogenic regulatory factor expression.

The amelioration of denervation atrophy by the beta-adrenoceptor agonist clenbuterol has led to the suggestion that the drug mimics or stimulates production of neurotrophic factors. Neurotrophic factors have profound effects on muscle growth, but the precise mechanisms through which this influence is exerted are unknown. The expression of myoD and myogenin, proteins that in turn regulate the transcription of tissue-specific genes during skeletal muscle differentiation, is controlled by innervation. In muscle undergoing denervation-induced atrophy, myoD and myogenin mRNAs increase. However, this is only partially reversed by electrical activity, thus implicating neurotrophic factors in regulation of these genes. Here we demonstrate that clenbuterol represses myoD and myogenin expression and decreases the levels of acetylcholine receptors in denervated muscles. The data provide the first evidence that the action of clenbuterol is directed through the neural axis.

Animals↗
PubMed1993

The control of chondrocyte differentiation during endochondral bone growth in vivo: changes in TGF-beta and the proto-oncogene c-myc.

The expression of transforming growth factor-beta and the c-myc proto-oncogene was studied in situ in the chondrocytes of the tibial growth plate of normal chicks and those with avian tibial dyschondroplasia in which the chondrocytes are developmentally arrested in the transitional phase between proliferation and differentiation. This results in an accumulation of unmineralised and avascular cartilage. Dyschondroplastic chicks showed reduced c-myc expression in the transitional chondrocytes but unaltered levels in the proliferating chondrocytes. Transforming growth factor-beta expression was reduced in the transitional chondrocytes of dyschondroplastic chicks. In areas where the lesion was being repaired there was evidence of increased expression of both c-myc protein and transforming growth factor-beta. Addition of 1,25-dihydroxyvitamin D to the diet, which is known to reduce the incidence of dyschondroplasia, resulted in an increase in c-myc production. These results suggest that both transforming growth factor-beta and the proto-oncogene c-myc may be important elements of the cascade of events that lead to chondrocyte differentiation, hypertrophy and mineralisation.

Alkaline Phosphatase↗