Fast and slow chicken skeletal muscles contain different alpha and beta tropomyosins

Molecular cloning and characterization of tropomyosin, a major allergen of Chironomus kiiensis, a dominant species of nonbiting midges in Korea

Chironomids are widely and abundantly distributed in the vicinity of standing waters. Larvae of Chironomus and some other genera are known to contain hemoglobins, which have been described as a major allergen, and the adults that have no hemoglobins also have been reported to contain allergens. In this study, we tried to establish the role of chironomid allergy and characterize the allergen of Chironomus kiiensis adults. Skin tests using C. kiiensis adult extracts were performed on patients with allergic symptoms. A cDNA library of C. kiiensis adults was screened with C. kiiensis immune mouse sera to identify allergens, and results were confirmed using skin test-positive human sera. Recombinant allergen was expressed in Escherichia coli and purified by affinity chromatography using nickel-nitrilotriacetic acid agarose to investigate its allergenic properties. Out of 275 allergic patients 14.2% showed a positive reaction to C. kiiensis adult crude extracts in the skin test. The tropomyosin was cloned by immunoscreening and expressed in Escherichia coli. C. kiiensis tropomyosin has a high homology at the amino acid level with tropomyosins which were previously known to be allergens in various arthropods (Periplaneta americana, 86.3%; Panulirus stimpson, 78.9%; Dermatophagoides pteronyssinus, 76.5%). Specific immunoglobulin E antibodies reacting to recombinant tropomyosin were detected in 17 (81%) of 21 patients whose skin test results were positive. Cross-reactivity against house dust mites and other insects was noticed with mouse anti-recombinant tropomyosin immune serum. C. kiiensis adults were shown to be an important source of inhalant allergens in Korea. Molecular cloning of C. kiiensis tropomyosin was performed and IgE reactivity was demonstrated using skin test-positive human sera. Recombinant tropomyosin will be useful for further studies or clinical applications.

Contractile protein isoforms in muscle development

The contractile proteins of skeletal muscle are often represented by families of very similar isoforms. Protein isoforms can result from the differential expression of multigene families or from multiple transcripts from a single gene via alternative splicing. In many cases the regulatory mechanisms that determine the accumulation of specific isoforms via alternative splicing or differential gene expression are being unraveled. However, the functional significance of expressing different proteins during muscle development remains a key issue that has not been resolved. It is widely believed that distinct isoforms within a family are uniquely adapted to muscles with different physiological properties, since separate isoform families are often coordinately regulated within functionally distinct muscle fiber types. It is also possible that different isoforms are functionally indistinguishable and represent an inherent genetic redundancy among critically important muscle proteins. The goal of this review is to assess the evidence that muscle proteins which exist as different isoforms in developing and mature skeletal and cardiac muscles are functionally unique. Since regulation of both transcription and alternative splicing within multigene families may also be an important factor determining the accumulation of specific protein isoforms, evidence that genetic regulation rather than protein coding information provides the functional basis of isoform diversity is also examined.

Avian cardiac tropomyosin gene produces tissue-specific isoforms through alternative RNA splicing

We have isolated a quail cardiac tropomyosin gene which encodes three distinct isoforms through the use of alternative exon splicing. Characterization of cDNA clones produced by this gene indicate that the gene encodes a unique 284 amino acid cardiac tropomyosin isoform, along with a 248 amino acid cytoskeletal and 284 amino acid smooth muscle isoforms. Northern analyses indicate that the gene is primarily expressed in cardiac muscle, with only minor expression of the cytoskeletal and smooth muscle transcripts.

The chicken gene encoding the alpha isoform of tropomyosin of fast-twitch muscle fibers: organization, expression and identification of the major proteins synthesized

The chicken gene alpha fTM encoding the alpha-tropomyosin of fast-twitch muscle fibers (alpha fTM) covers 20 kb and consists of 15 exons. From this gene, three types of mature transcripts (1.3 kb, 2 kb and 2.8 kb) are expressed through the use of alternative promoters, alternatively spliced exons and multiple 3' end processing. Northern analysis and S1 mapping have shown that the 1.3-kb transcript (exons 1a, 2b, 3, 4, 5, 6b, 7, 8, 9a-9b) is expressed in fast-twitch skeletal muscles and that 2-kb transcripts are expressed in smooth muscle (exons 1a, 2a, 3, 4, 5, 6b, 7, 8, 9d) and in fibroblasts (exons 1a, 2b, 3, 4, 5, 6a or 6b, 7, 8, 9d). These 2-kb transcripts encode distinct proteins which we have identified by two-dimensional (2D) gel electrophoresis. The 2.8-kb transcript which has not been so far characterized in birds is expressed in brain (exons 1b, 3, 4, 5, 6b, 7, 8, 9c-9d). This transcript has been characterized by a cDNA polymerase chain reaction assay and by S1 nuclease mapping. It produces a major TM isoform of chick brain which we have identified by 2D gels.

Biphasic expression of slow myosin light chains and slow tropomyosin isoforms during the development of the human quadriceps muscle

Using a two-dimensional electrophoresis technique coupled with sensitive silver staining, we have investigated the chronology of appearance of the myosin light chain and tropomyosin isoforms during early stages of human quadriceps development. Our results show that slow myosin light chains and the slow tropomyosin isoform are not detected at 6 weeks of gestation. These isoforms transiently appear between 12.5 weeks and 15 weeks of gestation and then disappear. The slow myosin light chains are re-expressed at 31 weeks of gestation and the slow tropomyosin isoform later at 36 weeks of gestation, and normally remained expressed into the adulthood. Our study thus reveals a biphasic expression of the slow myosin light chains and the slow tropomyosin isoform in developing human quadriceps muscle.

Identification of multiple variants of fast muscle troponin T in the chicken using monoclonal antibodies

Two monoclonal antibodies, T1/7 and T1/61, have been prepared which are specific for chicken fast muscle troponin T. Both are of the IgG gamma 1 subclass. Both antibodies cross-react strongly with human fast and chicken cardiac troponin T, but while T1/7 reacts weakly with rabbit fast troponin T, T1/61 does not. The antibodies can be used for fibre typing of both chicken and human muscle. The antibodies have been used to identify fast troponin T on two-dimensional maps of proteins from a variety of chicken muscles by electrophoretic transfer to nitrocellulose followed by immunoperoxidase staining. Using this technique five variant forms of fast troponin T have been identified. Two variants, fBT1 and fBT2, are expressed in breast muscle, while the other three, fLT1, fLT2 and fLT3 are expressed in leg muscle. Of the leg muscle variants, fLT1 and fLT2 correspond to the two forms described previously [Wilkinson, J.M., Moir, A.J.G. and Waterfield, M.D. (1984) Eur. J. Biochem. 143, 47-56]. The third variant, fLT3, has not been described before and is expressed in muscles which have a high content of slow fibres. In addition to these clearly defined variant forms immunostaining reveals multiple minor variants of troponin T present in leg muscle which may reflect complex RNA processing of the troponin T gene transcript.

Factors determining the subunit composition of tropomyosin in mammalian skeletal muscle

Adult rat fast-twitch skeletal muscle such as extensor digitorum longus contains alpha- and beta-tropomyosin subunits, as is the case in the corresponding muscles of rabbit. Adult rat soleus muscle contains beta-, gamma- and delta-tropomyosins, but no significant amounts of alpha-tropomyosin. Evidence for the presence of phosphorylated forms of at least three of the four tropomyosin subunit isoforms was obtained, particularly in developing muscle. Immediately after birth alpha- and beta-tropomyosins were the major components of skeletal muscle, in both fast-twitch and slow-twitch muscles. Differentiation into slow-twitch skeletal muscles was accompanied by a fall in the amount of alpha-tropomyosin subunit and its replacement with gamma- and delta-subunits. After denervation and during regeneration after injury, the tropomyosin composition of slow-twitch skeletal muscle changed to that associated with fast-twitch muscle. Thyroidectomy slowed down the changes in tropomyosin composition resulting from the denervation of soleus muscle. The results suggest that the 'ground state' of tropomyosin-gene expression in the skeletal muscle gives rise to alpha- and beta-tropomyosin subunits. Innervation by a 'slow-twitch' nerve is essential for the expression of the genes controlling gamma- and delta-subunits. There appears to be reciprocal relationship between expression of the gene controlling the synthesis of alpha-tropomyosin and those controlling the synthesis of gamma- and delta-tropomyosin subunits.

Changes in myofibrillar gene expression during fiber-type transformation in the claw closer muscles of the snapping shrimp, Alpheus heterochelis

Isotopes of a number of crustacean myofibrillar proteins have been identified with sodium dodecyl sulfate-polyacrylamide electrophoresis, and their distribution in muscles of the snapping shrimp has been examined. Fast-slow differences in distribution have been observed for myosin light chains and tropomyosin. In contrast, three troponin T subunits have been resolved, each specific to one of the three muscles examined. This result suggests that expression of crustacean contractile proteins is not accomplished by a simple coexpression of a battery of slow or fast isotopes. In addition, the expression of these proteins was examined during the quasi-developmental fiber-type transition of the main claw closer muscle during the reversal of claw asymmetry in response to the loss of the large snapper appendage. The changes observed appear similar to the cross-innervation induced changes in gene expression of vertebrate muscle.