Skewed X inactivation in a female MZ twin results in Duchenne muscular dystrophy.

One of female MZ twins presented with muscular dystrophy. Physical examination, creatine phosphokinase levels, and muscle biopsy were consistent with Duchenne muscular dystrophy (DMD). However, because of her sex she was diagnosed as having limb-girdle muscular dystrophy. With cDNA probes to the DMD gene, a gene deletion was detected in the twins and their mother. The de novo mutation which arose in the mother was shown by novel junction fragments generated by HindIII, PstI, or TaqI when probed with cDNA8. Additional evidence of a large gene deletion was given by novel SfiI junction fragments detected by probes p20, J-Bir, and J-66 on pulsed-field gel electrophoresis (PFGE). Immunoblot analysis of muscle from the affected twin showed dystrophin of normal size but of reduced amount. Immunofluorescent visualization of dystrophin revealed foci of dystrophin-positive fibers adjacent to foci of dystrophin-negative fibers. These data indicate that the affected twin is a manifesting carrier of an abnormal DMD gene, her myopathy being a direct result of underexpression of dystrophin. Cytogenetic analysis revealed normal karyotypes, eliminating the possibility of a translocation affecting DMD gene function. Both linkage analysis and DNA fingerprint analysis revealed that each twin has two different X chromosomes, eliminating the possibility of uniparental disomy as a mechanism for DMD expression. On the basis of methylation differences of the paternal and maternal X chromosomes in these MZ twins, we propose uneven lyonization (X chromosome inactivation) as the underlying mechanism for disease expression in the affected female.     

Organization of the Hamster Cumulus Extracellular Matrix: A Hyaluronate-Glycoprotein Gel which Modulates Sperm Access to the Oocyte

The mammalian oocyte-cumulus complex contains an extracellular matrix rich in hyaluronate. Recently, the microstructure of the hamster cumulus extracellular matrix was described (52). In the present work, we investigated the organization of this matrix. We employed freeze-substitution methodologies to investigate ultrastructural effects of various treatments, including sperm enzymes, on the matrix. Protease treatment resulted in disruption with a loss of the fibrillar structures and some expansion; in contrast, hyaluronidase treatment completely solubilized the matrix. EDTA extraction revealed that the fibrils are composed of fine filaments. A discrete region of the matrix immediately surrounding the oocyte, the corona radiata, was resistant to EDTA disruption. We found that hyaluronate is an ubiquitous constituent of the microstructural elements of this extracellular matrix. The matrix exhibits a carbohydrate:protein ratio of approximately 2:1. SDS-PAGE revealed that glycosylated polypeptides are bound to the matrix. The lectins LCA and WGA had differing affinities for these polypeptides, and bound ubiquitously to the intact matrix. The present data suggest that glycoprotein-hyaluronate interaction is critical for maintenance of the cumulus extracellular matrix microstructure and for its physical properties.     

Diphenoloxidases in various forms of myopathy which are transmitted by different genetic mechanisms

Summary In a previous article (Demos et al. 1981), we reported a significant and specific reduction of the activity index (AI) of the diphenoloxidases (DPox) in patients and heterozygotes with progressive Duchenne muscular dystrophy (DMD), which is transmitted genetically by female subjects by a sex-linked recessive mechanism (SLR). This same anomaly was detected in patients suffering from other types of dystrophy: Becker, limbgirdle, fascio-scapulo-humeral, and in heterozygotes, of either sex in diseases transmitted by an obviously recessive autosomic mechanism. These anomalies were detected using blood spots collected on absorbent paper and stored at 4°C for differnt periods. They were of the same type as had previously been detected using blood platelets (Demos 1973).     

The Roberts syndrome

Summary Four siblings with the autosomal recessive Roberts syndrome are reported, and we discuss the phenotypic overlap of this syndrome with other similar radial, aplasia syndromes.     

Constitutive and mitogen-induced production of T cell growth factor by stable T cell hybridoma lines

Stable T cell growth factor- (TCGF; IL 2) producing cloned T cell hybridoma lines were constructed by fusing murine alloantigen-activated T cells with the 8-azaguanine-resistant lymphoma line, BW5147. Many, but not all, clones of one of these hybridomas, i.e., hybridoma 24, secreted TCGF constitutively, but production was markedly enhanced by stimulation with T cell mitogens. Large numbers of TCGF-secreting hybridoma cells in a stable functional state could be obtained from histocompatible mice inoculated with cloned T cell hybridomas. Moreover, such in vivo-derived hybridoma cells could be stimulated sequentially with mitogen at least twice to secrete their biologically-active product, resulting in larger TCGF yields from the same cells. The secreted product of these T cell hybridoma lines resembled TCGF isolated from other cellular sources in that it: a) supported the growth of a TCGF-dependent T cell line; b) provided help for the induction of alloantigen-reactive cytotoxic T lymphocytes from thymocyte precursors; c) facilitated concanavalin A-induced mitogenic responses of low thymocyte numbers; d) had an apparent m.w. of 30,000 to 40,000 by gel filtration chromatography; and e) was eluted from DEAE-Sephacel ion-exchange chromatography columns by salt concentrations of 30 to 150 mM NaCl. The ability of these T cell hybridomas to grow in vivo and retain their functional characteristics in a stable form should prove useful in terms of providing large numbers of TCGF-secreting cells and studying in vivo aspects of the production of TCGF as well as other immunoregulatory mediators.     

The synthesis and deployment of filamin in chicken skeletal muscle

During myogenesis in vitro the actin-binding protein filamin is present in myoblasts and early fused cells and is associated with α-actinin-containing filament bundles, as judged by double immunofluorescence using antibodies specific for these two proteins. Approximately one day after cell fusion, yet before the development of a-actinin-containing Z line striations, filamin disappears from the cells. Later in myogenesis, several days after the appearance of α-actinin-containing Z line striations, filamin reappears and accumulates in the cells. Double immunofluorescence with antibodies to filamin and vimentin (or desmin) reveals that the newly appearing filamin localizes now to the myofibril Z line and is visible there shortly before vimentin or desmin becomes associated with the Z line. Immunofluorescent localization of filamin in isolated chicken skeletal myofibrils and Z disc sheets indicates that filamin has the same distribution as desmin and vimentin; it surrounds each myofibril Z disc and forms honeycomb-like networks within each Z plane of the muscle fiber. Filamin may thus be involved in the transition of desmin and vimentin to the Z disc. Analysis of whole-cell extracts by SDS-polyacrylamide gel electrophoresis and by immunoautoradiography shows that filamin is present in myoblasts and in myotubes early after cell fusion. Concomitant with the absence of filamin fluorescence during the subsequent few days of myogenesis, the quantity of filamin is markedly reduced. During this time, metabolic pulse-labeling with ³⁵S-methionine reveals that the synthetic rate of filamin is also markedly reduced. As filamin fluorescence appears at the Z line, the quantity of filamin and its synthetic rate both increase. The removal of filamin from the cells suggests that filamin either may not be required, or may actually interfere with a necessary process, during the early stages of sarcomere morphogenesis. These results also indicate that the periphery of the Z disc is assembled in at least two distinct steps during myogenesis.     

Modification of avian sarcoma proviral DNA sequences in nonpermissive XC cells but not in permissive chicken cells

For the first time, we present evidence with restriction enzymes HpaII and MspI which indicates that the proviral DNA sequence of avian sarcoma virus is modified by methylation in a nonpermissive rat cell line but not in permissive chicken cells. Some of the endogenous viral sequences in the permissive cells were also methylated. No 5-methylcytosine could be detected in the unintegrated viral DNA.     

Glucokinase in bird liver: a membrane bound enzyme

There have been numerous reports that liver of birds contain only isoenzymes of the low K_M hexokinases, but lack the high K_M glucokinase. We describe here the presence of glucokinase in livers of chicken and Japanese quail. The enzyme is membrane bound and is solubilized by vigorous mechanical disruption of the tissue. With gentle homogenization the glucokinase is recovered upon centrifugation in the 1000g pellet, from which it may be liberated by prolonged sonication. It appears to be localized in the cell plasma membrane. The activities of hexokinase and glucokinase appear to be about equal in liver parenchyma of fed chicken, but in that of Japanese quail the activity of glucokinase exceeds greatly that of hexokinase.