The increase in hexokinase activity in hereditary avian muscular dystrophy.

Hexokinase activity was found to be increased in both the more severely affected red (thigh) muscle of dystrophic chickens. The increase in activity was largely associated with the particulate fraction. These findings may indicate early events in the pathogenesis of avian muscular dystrophy.     

An effect of avian hereditary muscular dystrophy on the reaction of troponin-C with its antibody

Antibody prepared against troponin-C, the calcium binding component of the troponin complex, was reacted with I band segments, and the distribution of antibody binding was assessed by immuno-electron microscopy. The I segments were isolated from glycerinated pectoral muscle which was prepared from normal adult chickens and from dystrophic chickens of strain 308. The antibody was deposited at 384 Å ± 7 Å intervals along the thin filaments of the normal muscle. In contrast to the normal controls the dystrophic muscle did not exhibit a distinct periodicity when reacted with anti-troponin-C. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate revealed that although protein bands corresponding to troponin-C could be observed in the gels of the dystrophic preparations, the troponin-C band had migrated slower than that from normal thin filaments. It is concluded that avian muscular dystrophy produces an alteration of the structure of troponin-C resulting in (1) an inability of the protein to combine with its specific antibody and (2) a change in its electrophoretic behavior.     

Elevation of calmodulin in avian muscular dystrophy

In an attempt to understand the mechanism of calcium accumulation in myopathies, changes in the major calcium-binding protein, calmodulin, was studied in genetically dystrophic chickens. Measurements by radioimmunoassay revealed an increase in the calmodulin concentration of dystrophic chicken muscles. Poly A-containing RNA(s) of fast and slow muscles from the normal and dystrophic chicks were hybridized with [32P]-labeled calmodulin cDNA probe by the dot-hybridization technique. Densitometric scan of the autoradiogram showed that the calmodulin mRNA levels of dystrophic fast muscles (pectoralis and posterior latissimus dorsi) were approximately two-fold higher than those of the corresponding normal muscles. No significant change in calmodulin and calmodulin messenger RNA of slow muscle (ALD) was found in dystrophic chickens. Our results suggest that increased calcium flux within the dystrophic muscle may be modulated by calmodulin.     

Linkage studies in Emery-Dreifuss muscular dystrophy

We report linkage studies between Emery-Dreifuss muscular dystrophy (EDMD) and polymorphic probes from the long arm of chromosome X in two pedigrees. The results don't show significant linkage but are consistent with previous localisation of EDMD in Xq28. Further studies will be necessary to apply molecular biology to genetic counselling and prenatal diagnosis of this disease.     

Myofibrillar creatine kinase in Duchenne and avian muscular dystrophy

The presence and activity of the fraction of creatine kinase (CK) which was associated with myofibrils and located in the M line of the sarcomeres was determined in normal and dystrophic avian muscle and in normal and dystrophic (Duchenne) human muscle. Myofibrils were isolated from homogenates of muscle and washed nine times so as to remove nonmyofibrillar CK. In myofibrils from dystrophic muscle the enzyme CK was localized to the M line using immunofluorescent techniques and was enzymatically active. These results suggest that in both avian and Duchenne muscular dystrophy, there is not a myofibrillar disorder of the phosphocreatine shuttle.     

Thyroidal involvement in the expression of avian muscular dystrophy

We showed previously that propylthiouracil (PTU), a thyroid inhibitor, could alleviate several major signs of hereditary muscular dystrophy in chickens. The goals of the present investigation were to: (1) determine whether a nearly athyroid condition (achieved within two days after hatching by surgical thyroidectomy plus PTU) during an 11-day period beneficially affects the dystrophic condition when followed by triiodothyronine (T3) replacement to 33 days of age; (2) determine the beneficial effects on the expression of avian dystrophy when the thyroidectomized-PTU-treated chickens received a wide range of moderate to low T3 replacement doses beginning by two days after thyroidectomy; and (3) examine the thyroid hormone receptor system in dystrophic muscle for a possible abnormality. Thyroid deprivation increased muscle function (righting ability) and reduced plasma creatine kinase activity in dystrophic chickens. The major thyroid-related abnormality in dystrophic pectoralis muscles was an increased maximum binding capacity of solubilized nuclear T3 receptors.     

Structure of myosin heavy chain in avian muscular dystrophy

We have studied the structure of myosin heavy chain (MHC) in the pectoralis muscle of genetically dystrophic (Connecticut Strain) and White Leghorn chicks. MHC was alkylated with N-ethylmaleimide, purified by Sepharose-4B chromatography, and cleaved with cyanogen bromide. The MHC CNBr peptides were analyzed by one-dimensional and two-dimensional isoelectric focusing/sodium dodecyl sulfate gradient gels and by amino acid sequencing. Specific changes were detected in the gel patterns which could be correlated with the loss of muscle function as measured by the exhaustion score (the ability of chicks to rise from a reclining position) in three experimental groups (exhaustion scores: less than 3, 10-20, greater than 30). We have also examined the amino acid sequence of a 3-methyl-histidine-containing peptide which originates from the 20-kDa fragment of pectoralis muscle MHC in dystrophic chicks: Val-Leu-Asn-Ala-Ser-Ala-Ile-Pro-Glu-Gly-*Gln-Phe-*Ile-Asp-Ser-Lys-Lys- Ala-Ser-Leu-Gln-Lys-Leu-Gly-Ser-Ile-Asp-Val-(Asp, 3-methylhistidine, Gln). Comparison of the homologous MHC sequences shows two positions at which MHC from dystrophic chicks differs from that of the White Leghorn chicks *(Glu----Gln and Met----Ile). Thus, both the peptide map and sequence analyses demonstrate that in avian muscular dystrophy an abnormal pectoralis MHC is synthesized. It is not yet clear whether the "dystrophic" MHC is a variant MHC or if it arises from the abnormal expression of an earlier developmental form (embryonic or neonatal) of pectoralis muscle MHC.     

Genetic studies of a muscular dystrophy of mink.

Analysis of breeding data revealed that the muscular dystrophy trait in a pedigree of mink is transmitted in an autosomal recessive manner. Variation in skeletal muscle fiber diameter size is the most pronounced and consistent change in the dystrophic mink. Other changes include centralization of nuclei, degenerative change, increase in endomysial and perimysial connective tissue, and regenerative attempts. These changes are not present in known heterozygotes.     

Beneficial effects of anti-growth hormone antiserum in avian muscular dystrophy

Human subjects and mice have been found to have a milder progression of muscular dystrophy when the disease is associated with genotypically determined dwarfism. In this paper we describe an experimental test for reducing growth hormone in dystrophic chickens that uses rabbit anti-chicken growth hormone anti-serum (anti-cGH). Antiserum was injected daily into dystrophic (line 413) male chickens from day 1 to day 8 after hatching. Dystrophic chickens injected with anti-cGH maintained a significantly higher score in the standardized test for righting ability (P less than 0.001-0.051) from 3 to 9 1/2 wk after hatching when compared with dystrophic controls. The observed prolongation of the functional ability of injected dystrophic animals suggests that growth hormone plays a role in potentiating the symptoms of dystrophy in chickens.     

Glucocorticoids in muscular dystrophy: beneficial effects of dexamethasone on avian myopathy

A corticosteroid with mixed glucocorticoid-mineralocorticoid actions was previously shown to improve neuromuscular function in muscular dystrophic chickens. The significance of that finding was recently underscored by reports that a mixed-action corticosteroid improved muscle function in Duchenne dystrophy patients, albeit at high doses. In the present study a pure glucocorticoid improved function and retarded muscle histopathology in the chicken, but a pure mineralocorticoid did not. These observations suggest that elucidation of mechanisms by which glucocorticoids beneficially affect dystrophic muscle could lead to development of more effective therapies.     

Duchenne muscular dystrophy.

Progress in understanding the role of dystrophin raises promising hopes for a treatment for Duchenne muscular dystrophy. In addition, great improvements have been made in the ability to diagnose this disease using simple molecular methods.