Control of gene expression in muscle development

Isolation of human cardiac troponin T and localization of epitopes recognized by monoclonal antibodies to cardiac troponin T

Human cardiac troponin T has been isolated and its properties compared with those of rabbit skeletal and bovine cardiac troponin T. Seven monoclonal antibodies to troponin T have been obtained. Two antibodies cross-reacted with both cardiac and skeletal troponin T and recognized epitopes located between residues 98-177 of bovine cardiac troponin T. Five other antibodies were specific for cardiac troponin T and recognized antigenic determinants located between residues 180-258 of bovine cardiac troponin T. Localization of antigenic determinants in the central part of troponin T seems to be due to the high hydrophilicity and flexibility of this part of the molecule. The monoclonal antibodies thus obtained may be used for diagnosing various types of human heart diseases.

Comparison of the structure of two cardiac troponin T isoforms

Two isoforms of troponin T have been isolated from bovine cardiac muscle. One isoform has an Mr of 31000 and a pI at about 7.1, the corresponding values for the second isoform being 33000 and 6.5. Both isoforms have identical C- and N-terminal sequences, and, according to the data from tryptic-peptide mapping, a similar structure of the central and C-terminal domains. The large N-terminal peptides of troponin T isoforms differ in the content of glutamine/glutamic acid and alanine. It is concluded that the isoform with Mr 33000 has an additional peptide enriched with glutamic acid and alanine that is inserted between the N-terminal pentapeptide and the cysteine located 40-60 residues from the N-terminus.

Histone H1(0): a maintainer of the differentiated cell state?

Functional and structural effects of histones H1 and H1(0) were studied on isolated chromatin and nuclei from embryonic skeletal muscle as well as on cultured cells. The results showed that: H1 was responsible for a greater compaction of chromatin than H1(0) as evidenced by sedimentation. In contrast, H1(0) inhibited DNA synthesis in chromatin and cells to a greater extent than H1. No significant difference between the two histones on RNA synthesis inhibition was observed. histones H1 and H1(0) evidenced a quantitative increase in developing muscle cells. The results indicate that H1(0) may not be the inducer of the differentiated cell state, but rather assists in the maintenance of that state.

Evidence for transcriptional regulation of the myosin heavy chain gene during myogenesis

One of the changes accompanying skeletal muscle cell (myoblast) fusion is a dramatic increase in synthesis of muscle specific proteins, one of which is myosin. The underlying mechanism for this burst in synthesis is not yet understood but may occur by two mechanisms: (a) gradual storage of mRNA and translational control as found by others or (b) gene activation and rapid synthesis of mRNA for immediate translation. In this paper we show that the myosin gene changes its organization such that postfusion skeletal muscle cells show an increased susceptibility to DNase I, a recognized probe for gene activation. We also show that this change accompanies an increase in rate of transcription and an increased cell content of myosin heavy chain mRNA. This work shows that transcriptional control is an important mechanism during muscle cell development in addition to the translational control shown by other workers.