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T Parr

Publications and source records attributed to T Parr.

24 records · Page 2Linked to original sources
PubMed1994

Analysis of the phasing of four spectrin-like repeats in alpha-actinin.

Selected fragments of the central rod of chicken gizzard alpha-actinin were expressed as fusion proteins in Escherichia coli, with the aim of determining the positions in the sequence of the four successive spectrin-like repeats that make up this domain. The criteria for an independently folding unit were resistance to proteolysis and the high alpha helicity characteristic of the native protein. Sequences containing repeats 1-4, 2-4, 3-4 and 4 all generated stable fragments on digestion with trypsin and/or thermolysin and N-terminal sequencing gave the most probable starting position of each repeat. The sequences of all four inferred repeats and the sequences of the entire rod, were separately expressed and were shown to assume a stable, protease-resistant fold in solution. The repeat boundaries established in this way differed from those originally deduced from sequence alignments; the N-terminal boundaries of the repeats were 14-24 residues nearer the C-terminus than predicted. The ability to express individual repeats should facilitate identification of the binding sites for the cytoplasmic domains of beta 1 integrins and intercellular cell adhesion molecule-1 which have been localised to the rod domain of alpha-actinin.

Actinin↗
PubMed1992

A chick skeletal-muscle alpha-actinin gene gives rise to two alternatively spliced isoforms which differ in the EF-hand Ca(2+)-binding domain.

A chick non-muscle alpha-actinin cDNA probe encoding the EF-hand region of molecule was used to screen a lambda gt10 chick brain cDNA library from 14-day embryos. A partial 2.1-kb alpha-actinin cDNA was isolated (8W cDNA) which encoded a protein identical to chick skeletal-muscle alpha-actinin, except in the C-terminal part of the first EF hand. In the variant, the 22 residues found in the skeletal-muscle isoform were replaced by a stretch of 26 unique residues. Analysis of the structure of the skeletal-muscle alpha-actinin gene showed that the region of divergence was encoded by two exons which are alternatively spliced. Quantitative reverse transcriptase/polymerase chain reaction (RT/PCR) was used to investigate the levels of the alpha-actinin transcripts in various tissues. The skeletal-muscle alpha-actinin variant was expressed at low levels in brain, liver and spleen, but could not be detected in skeletal muscle. Surprisingly, skeletal-muscle alpha-actinin mRNA was also expressed in brain, liver and spleen. The RT/PCR products were authenticated by using diagnostic restriction enzyme sites and by sequencing. The splice variant derived from the skeletal-muscle alpha-actinin gene was also detected in a variety of cDNA libraries from both adult and embryonic tissues by PCR. Although a transcript encoding this alpha-actinin splice variant is expressed in non-muscle tissues, neither of the two EF-hands would be predicted to be functional, making it unlikely to be a typical non-muscle isoform which are calcium-sensitive with respect to binding actin. The two vertebrate non-muscle alpha-actinins sequenced to date also have a spacer of five amino acids between the two EF hands, whereas in the variant, the spacer is just four residues in length. Further analysis will be required before this alpha-actinin isoform, which we refer to as SKv, can be classified as muscle or non-muscle alpha-actinin. We propose a new nomenclature to describe the various alpha-actinin genes and their transcripts.

Actinin↗
PubMed1992

Changes in calpain and calpastatin mRNA induced by beta-adrenergic stimulation of bovine skeletal muscle.

Administration of beta-adrenergic agonists to mammals can produce skeletal muscle hypertrophy in some species and muscle types. The growth-promoting effect appears to be due to suppression of protein breakdown rather than stimulation of synthesis, although evidence from turnover studies is equivocal. In ovine muscle, changes in the activity of the calcium dependent neutral proteinases (calpains I and II) and their specific inhibitor (calpastatin) accompany beta-agonist-induced hypertrophy. These observations suggest that the calpain system is involved in myofibrillar protein turnover in some way. Alternatively, the relationship with hypertrophy may be indirect, since the calpains also interact with hormone and growth-factor receptors, protein kinase C and transcription factors, in addition to a range of membrane, cytoskeletal and nuclear proteins. In the present study, attempts have been made to determine if the beta-agonist-induced effects on the calpain system are associated with corresponding changes in specific mRNA. The activity of both calpain isoforms and calpastatin was measured in bovine longissimus dorsi samples from trials in which test animals were treated with the beta agonist cimaterol. Total RNA was extracted from the muscle samples. A cDNA probe for calpastatin mRNA was generated from bovine RNA by the polymerase chain reaction. This cDNA and a human calpain-II large-subunit cDNA were used to detect specific mRNA by Northern-blot analysis. beta-agonist treatment of Friesian steers caused significant longissimus dorsi hypertrophy. Increases in muscle mass (+37%, P less than 0.005), calpain-II specific activity (+27%, P less than 0.05) and calpastatin-specific activity (+76%, P less than 0.05) were found in treated animals. Total RNA was unchanged, but there was a 96% overall increase in calpastatin mRNA and a 30% increase in calpain-II large-subunit mRNA in muscle from treated animals. The mRNA changes are similar in direction and degree to the activity changes. Both calpain-II large subunit and inhibitor expression may therefore be stimulated by agonist action at the level of transcription or mRNA stabilisation. Multiple calpastatin mRNA species were detected in steers, as reported for other species. Differential changes in these messages, induced by the beta agonist, suggest that expression or stability of alternative mRNA species may be a factor in calpastatin regulation.

Adrenergic beta-Agonists↗
PubMed1992

Effect of beta-agonists on expression of calpain and calpastatin activity in skeletal muscle.

Administration of beta-adrenergic agonists to domestic species can lead to skeletal muscle hypertrophy, probably by reducing the rate of myofibrillar protein breakdown. Myofibrillar breakdown is associated with the calcium-dependent proteinase system (calpains I,II and calpastatin) whose activity also changes during beta-agonist treatment. A number of growth trials using the agonists cimaterol and clenbuterol with cattle, sheep, chicken and rat are reported which suggest a general mechanism whereby beta-agonists reduce calpain I activity, but increase calpain II and calpastatin activity in skeletal muscle. Parallel changes in specific mRNAs indicate that changes in gene expression or stabilisation of mRNA could in part explain the changes in activity.

Adrenergic beta-Agonists↗
PubMedDate not supplied

Insulin exposure and unifying aging.

BACKGROUND: Absence of a widely agreed upon central paradigm for mammalian aging. OBJECTIVE: Detailed elaboration of a proposed mammalian aging paradigm. METHODS: Elaboration of a new theoretical model. RESULTS: Hormonal imbalance-growth factor exposure theory (HI-GFE theory) can account for two major aging phenomena: (1) decline in mammalian 'reserve capacity' and consequent rise of diseases of maintenance, and (2) rise then peaking of most age-associated proliferative diseases. Reserve capacity decline via gradual decline in mitochondrial maximal energy production (state 3) accounts for the gradual redirection of declined maximal energy production toward survival functions like ion pumping to the relative detriment of RNA and protein synthesis as seen in lesser synthetic rates and slower turnover with consequent gradual cellular impairment. Developmental program triggered, and over-ample nutritionally driven, growth factor exposure in youth to middle age encourages promotional events that lead to proliferative diseases that rise coincident to rapidly declining reserve capacity and cumulative increased mutational status of age. CONCLUSIONS: Declining mitochondrial state 3 aging energy production status is easily and safely reversible with probable consequences of greatly postponing the decline in overall 'reserve capacity' which may also improve insulin: growth hormone balance and result in lower overall growth factor exposure and consequent longer healthy life of a potentially greater magnitude increase in life spans than that seen in calorie-restricted animals.

Aging↗