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H F Epstein

Publications and source records attributed to H F Epstein.

At least 55 records · Page 3Linked to original sources
PubMed1991

Molecular biology of human muscle disease.

The molecular revolution that is transforming the entire biomedical field has had far-reaching impact in its application to inherited human muscle disease. The gene for Duchenne muscular dystrophy was one of the first cloned without knowledge of the defective protein product. This success was based upon the availability of key chromosomal aberrations that provided molecular landmarks for the disease locus. Subsequent discoveries regarding the mode of expression for this gene, the structure and localization of its protein product dystrophin, and molecular diagnosis of affected and carrier individuals constitute a paradigm for investigation of human genetics. Finding the gene for myotonic muscular dystrophy is requiring the brute force approach of cloning several million bases of DNA, identifying expressed sequences, and characterizing candidate genes. The gene that causes hypertrophic cardiomyopathy has been found serendipitously to be one of the genetic markers on chromosome 14, the beta myosin heavy chain.

Humans↗
PubMed1990

Modulation of muscle gene expression in Caenorhabditis elegans: differential levels of transcripts, mRNAs, and polypeptides for thick filament proteins during nematode development.

The body-wall muscle cells of the nematode Caenorhabditis elegans produce thick filaments during embryonic, larval, and adult stages. These thick filaments contain two myosin isoforms, A and B, which assemble into different zones along the 10-microns lengths. Paramyosin, a protein homologous to myosin rods, forms a substratum for the myosins. The three filament proteins are encoded by different genes: myo-3 V (myosin heavy chain A), unc-54 I (myosin heavy chain B), and unc-15 I (paramyosin). The relative expression of these genes has been studied by run-on nuclear transcription in vitro, hybridization of accumulated mRNA, and immunochemical determination of specific polypeptide accumulation. In late larval nematodes (L4), the relative levels of nuclear run-on transcription per mol of probe are 6.4 unc-54:2.4 myo-3:1.0 unc-15. Similarly, the relative levels of immunospecific proteins are 4.5 unc-15:3.1 unc-54:1.0 myo-3. Most strikingly, the relative mRNA amounts are 50.0 unc-54:12.4 unc-15:1.0 myo-3. Thus, the orders of relative abundance and the quantitative relations of expression of the three functionally related genes change from transcriptional activities to final accumulated product of thick filament proteins. Modulation of the expression appears to involve processes affecting accumulation of mRNA and protein. The great difference in accumulation of the mRNAs for the two myosin heavy chain isoforms A and B may be related to the different roles of the myosins in thick filament assembly.

Animals↗
PubMed1988

Purified thick filaments from the nematode Caenorhabditis elegans: evidence for multiple proteins associated with core structures.

The thick filaments of the nematode, Caenorhabditis elegans, arising predominantly from the body-wall muscles, contain two myosin isoforms and paramyosin as their major proteins. The two myosins are located in distinct regions of the surfaces, while paramyosin is located within the backbones of the filaments. Tubular structures constitute the cores of the polar regions, and electron-dense material is present in the cores of the central regions (Epstein, H.F., D.M. Miller, I. Ortiz, and G.C. Berliner. 1985. J. Cell Biol. 100:904-915). Biochemical, genetic, and immunological experiments indicate that the two myosins and paramyosin are not necessary core components (Epstein, H.F., I. Ortiz, and L.A. Traeger Mackinnon. 1986. J. Cell Biol. 103:985-993). The existence of the core structures suggests, therefore, that additional proteins may be associated with thick filaments in C. elegans. To biochemically detect minor associated proteins, a new procedure for the isolation of thick filaments of high purity and structural preservation has been developed. The final step, glycerol gradient centrifugation, yielded fractions that are contaminated by, at most, 1-2% with actin, tropomyosin, or ribosome-associated proteins on the basis of Coomassie Blue staining and electron microscopy. Silver staining and radioautography of gel electrophoretograms of unlabeled and 35S-labeled proteins, respectively, revealed at least 10 additional bands that cosedimented with thick filaments in glycerol gradients. Core structures prepared from wild-type thick filaments contained at least six of these thick filament-associated protein bands. The six proteins also cosedimented with thick filaments purified by gradient centrifugation from CB190 mutants lacking myosin heavy chain B and from CB1214 mutants lacking paramyosin. For these reasons, we propose that the six associated proteins are potential candidates for putative components of core structures in the thick filaments of body-wall muscles of C. elegans.

Animals↗
PubMed1987

Assemblages of multiple thick filaments in nematode mutants.

A spectrum of thick filament-related structures exhibiting novel structural features is isolated in addition to the normal thick filaments from unc-15 and unc-82 mutants of Caenorhabditis elegans. Many assemblages have multiple myosin-coated filaments extending from both ends of central domains exhibiting paracrystalline paramyosin. The filament ends resemble the polar core structures of native thick filaments. Assemblages with filaments at only one end and short thick filaments that branch are also present. This spectrum of novel structures accumulates at high levels in specific mutants due to alterations in paramyosin or other interacting proteins. The multifilament structures are either alternative assemblages of thick filament proteins and substructures or usually transient nucleation centres active in the assembly of thick filaments which are favoured under mutant conditions.

Actin Cytoskeleton↗
PubMed1987

Immunochemical localization of myosin heavy chain isoforms and paramyosin in developmentally and structurally diverse muscle cell types of the nematode Caenorhabditis elegans.

The nematode Caenorhabditis elegans contains two major groups of muscle cells that exhibit organized sarcomeres: the body wall and pharyngeal muscles. Several additional groups of muscle cells of more limited mass and spatial distribution include the vulval muscles of hermaphrodites, the male sex muscles, the anal-intestinal muscles, and the gonadal sheath of the hermaphrodite. These muscle groups do not exhibit sarcomeres and therefore may be considered smooth. Each muscle cell has been shown to have a specific origin in embryonic cell lineages and differentiation, either embryonically or postembryonically (Sulston, J. E., and H. R. Horvitz. 1977. Dev. Biol. 56:110-156; Sulston, J. E., E. Schierenberg, J. White, and J. N. Thomson. 1983. Dev. Biol. 100:64-119). Each muscle type exhibits a unique combination of lineage and onset of differentiation at the cellular level. Biochemically characterized monoclonal antibodies to myosin heavy chains A, B, C, and D and to paramyosin have been used in immunochemical localization experiments. Paramyosin is detected by immunofluorescence in all muscle cells. Myosin heavy chains C and D are limited to the pharyngeal muscle cells, whereas myosin heavy chains A and B are localized not only within the sarcomeres of body wall muscle cells, as reported previously, but to the smooth muscle cells of the minor groups as well. Myosin heavy chains A and B and paramyosin proteins appear to be compatible with functionally and structurally distinct muscle cell types that arise by multiple developmental pathways.

Animals↗
PubMed1986

The alteration of myosin isoform compartmentation in specific mutants of Caenorhabditis elegans.

Myosin isoforms A and B are located at the surface of the central and polar regions, respectively, of thick filaments in body muscle cells of Caenorhabditis elegans, whereas paramyosin and a distinct core structure comprise the backbones of these filaments. Thick filaments and related structures were isolated from nematode mutants that have altered thick filament protein compositions. These mutant filaments and their complexes with specific antibodies were studied by electron microscopy to determine the distribution of the two myosins. The compartmentation of the two myosin isoforms in body wall muscle thick filaments depends not only upon the intrinsic properties of the myosins but their interactions with other components such as paramyosin and their relative quantities determined by synthesis.

Animals↗
PubMed1985

Myosin and paramyosin are organized about a newly identified core structure.

Myosin isoforms A and B are differentially localized to the central and polar regions, respectively, of thick filaments in body wall muscle cells of Caenorhabditis elegans (Miller, D. M. III, I. Ortiz, G. C. Berliner, and H. F. Epstein, 1983, Cell, 34:477-490). Biochemical and electron microscope studies of KCl-dissociated filaments show that the myosin isoforms occupy a surface domain, paramyosin constitutes an intermediate domain, and a newly identified core structure exists. The diameters of the thick filaments vary significantly from 33.4 nm centrally to 14.0 nm near the ends. The latter value is comparable to the 15.2 nm diameter of the core structures. The internal density of the filament core appears solid medially and hollow at the poles. The differentiation of thick filament structure into supramolecular domains possessing specific substructures of characteristic stabilities suggests a sequential mode for thick filament assembly. In this model, the two myosin isoforms have distinct roles in assembly. The behavior of the myosins, including nucleation of assembly and determination of filament length, depend upon paramyosin and the core structure as well as their intrinsic molecular properties.

Animals↗
PubMed1983

Transition in the thin-filament arrangement in rat skeletal muscle.

The transition in thin-filament arrangement from tetragonal near the Z-band to trigonal in the A-band was investigated by computer-assisted analysis of thin-filament arrangement in serially cross-sectioned rat muscle. Extensor digitorum longus (EDL; fast) muscle from adult rats and adult, 9-day and 3-day neonatal soleus (slow) muscle were serially cross-sectioned from the H-zone of one sarcomere to the H-zone of an adjacent sarcomere. Thin-filament arrangement was analysed throughout the I-band, and particularly at three levels of the sarcomere: in the I-band, one section (0.06 microns) from the Z-band; six sections (0.36 microns) from the Z-band; in the A-band, two sections from the A-I junction (0.72 microns from the Z-band). Data for radical distributions and annular distributions were obtained by computer. In all muscles studies, thin-filament arrangement exhibited four-neighbour ordering throughout the I-band. Thin-filament arrangement exhibited three-neighbour ordering only in the A-band. The transition in thin-filament arrangement from four-neighbour to three-neighbour ordering occurred within 0.12 microns of the A-I junction in muscles fixed at rest length. In adult soleus that had been stretched 20% so that the A-I junction moved away from the N2-line, the transition in thin-filament arrangement occurred in the I-band within a region 0.4-0.5 microns from the Z-band. This region corresponds to the N2-line region of the I-band. Thus, the transition from four-neighbour to three-neighbour ordering occurs in the I-band independent of the thin filament-thick filament interaction. We conclude that some inherent feature of the I-band or thin filament-thin filament interaction imposes a four-neighbour ordering on thin filaments from the Z-band to the N2-line.

Animals↗
PubMed1983

Differential localization of two myosins within nematode thick filaments.

The body wall muscle cells of the nematode, Caenorhabditis elegans, contain two unique types of myosin heavy chain, A and B. We have utilized an immunochemical approach to define the structural location of these two myosins within body wall muscle thick filaments. By immunofluorescence microscopy, myosin B antibodies label the thick filament-containing A-bands of body wall muscle with the exception of a thin gap at the center of each A-band, and myosin A antibodies react to form a medial fluorescent stripe within each A-band. The complexes of these monoclonal antibodies with isolated thick filaments were negatively stained and studied by electron microscopy. The myosin B antibody reacts with the polar regions of all filaments but does not react with a central 0.9 micron zone. The myosin A antibody reacts with a central 1.8 micron zone in all filaments but does not react with the polar regions.

Animals↗
PubMed1982

Muscle differentiation in normal and cleavage-arrested mutant embryos of Caenorhabditis elegans.

The differentiation of body-wall muscle cells was studied in the nematode Caenorhabditis elegans. Specific antibodies to myosin and paramyosin, major protein constituents of differentiated muscle, react with mesodermal cells in wild-type embryos towards the end of the first half of embryogenesis. Immunoreactive cells (2-16) first appear in embryos with 400-450 of the 550 cells present at hatching. Such embryos have developed at 25.5 degrees C for 4-4 1/2 hr beyond the two-cell stage. As development proceeds, a maximum of 81 immunoreactive cells forms four columns running anterior-posterior. Each column is composed of two lines of tightly opposed round cells, which then elongate into spindle-shaped cells. Mutant embryos in which cleavage arrests prematurely also generate cells that produce myosin and paramyosin. The initiation of muscle differentiation appears to be independent of the number of cell or nuclear divisions within a lineage or of the proliferation of other cells. These results suggest that the biosynthesis of muscle-specific proteins by nematode embryonic muscle cells is regulated by mechanisms intrinsic to these cells.

Animals↗
PubMed1980

Identification of genetic elements associated with muscle structure in the nematode Caenorhabditis elegans.

A search for new mutants with altered body-wall muscle cell structure has been undertaken in the nematode C elegans. One-hundred seventeen mutants were isolated after mutagenesis with ethyl methanesulfonate or ultraviolet light, enrichment by a motility-requiring test, and screening by polarized light microscopy; 102 of these mutants were in ten previously established genes, whereas 15 mutants permitted the identification of seven new complementation groups in C elegans. Two of the new genes map on linkage group I (unc-94 and unc-95) and four genes are sex linked (unc-96, unc-97, unc-98, and unc-99). One complementation group (unc-100) could not be mapped because of the special characteristics of its cohort mutants. Representative mutants of the mapped genes were examined by polarized light and electron microscopy. All of the mutants exhibit disruptions of the normal A and I band organization of thick and thin filaments. Several of the mutants produce collections of thin filament-like structures. In one of these cases, HE177 demonstrated collections of somewhat wider, intermediate-sized filaments as well, and the HE195 mutant produces paracrystalline aggregates of thin filaments amidst looser arrangements of similar structures. The mutants in newly identified genes, as well as the new mutants in previously established genetic loci, have promise as tools in the study of myofibrillar assembly and function. Among the 22 complementation groups associated with body-wall structure in C elegans, it is likely that some genes code for regulatory and morphogenetic functions in addition to the well-studied structural, contractile, and calcium-associated proteins in muscle.

Animals↗
PubMed1980

Mutants altering coordinate synthesis of specific myosins during nematode muscle development.

Mutations in the unc-52 gene on linkage group II retard the construction of body-wall muscle sarcomeres during larval development in the nematode Caenorhabditis elegans. Unc-52 mutants show decreased accumulation of myosin heavy chains relative to other polypeptides during larval development, correlating with the structural retardation. Pulse radiolabeling experiments show that decreased synthesis of specific body-wall myosin heavy chains that are encoded by the unc-54 gene on linkage group I is responsible for the defective myosin accumulation. In the wild type, a constant ratio of the synthesis of the unc-54-coded myosin B to myosin A, about 2:1, is maintained during the larval stages in which the synthesis of both myosins increases exponentially and rapid sarcomere growth and addition ensues. During the first 26 hr of larval development, before any structural or behavioral effects of unc-52 mutations are apparent, the synthesis of myosin heavy chains is also normal. By 38 hr, decreased synthesis of myosin B is detected in the unc-52 mutant SU200, when sarcomere growth slows considerably. The effects of mutation in the unc-52 locus are trans acting upon the synthesis of unc-54-coded myosin in a specific set of muscle cells during a defined period of larval development.

Animals↗