Transitory expression of Thy 1 antigen in skeletal muscle development

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A cell surface differentiation antigen known as Thy-1 (formerly called theta) is expressed during development of brain and thymocytes in both rat and mouse. Thy-1 is present in brain and on thymocytes throughout adult life, as well as on a subpopulation of peripheral lymphocytes. Both rat and mouse fibroblasts, and some fibroblastic cell lines, express Thy-1 in vitro and mouse Thy-1 has been reported on epidermal cells and a mammary tumor. The Thy-1 antigen has been reported lacking in other adult tissues, including muscle. Evidence is presented for an antigen with the serologic specificity of Thy-1 on rat myogenic cell lines and embryonic rat muscle differentiating in vitro. The presence of the antigen was transitory, being expressed on myoblasts and newly developed myotubes, but disappearing as myotubes differentiated. Immunofluorescence studies of Thy-1 in cultured fetal muscle are complicated by the presence of fibroblasts, which express Thy-1. The modified spindle shape of a typical myoblast distinguishes it from flattened irregular-shaped fibroblasts. In early primary cultures all cells fluoresced with anti thymocyte serum (ATS), the pattern on primary myoblasts being similar to L6 myoblasts. The density of fluorescent speckles on individual primary myoblasts varied considerably, however. Three further articles giving evidence for the Thy-1 specificity of immunofluorescence on cultured muscle cells are enumerated. The occurrence on myoblasts and immature myotubes of an antigen characteristic of thymocytes represents an unexplained association between muscle and thymus. Others include: the presence of striated muscle ('myoid') cells as a constituent of normal mammalian, avian and reptilian thymuses; the presence in rat thymus of nicotinic acetylcholine receptors characteristic of muscle; the concurrence of pathologic lesions in thymus and muscle in at least two spontaneous disease processes, myasthenia gravis and murine muscular dystrophy; the reported in vivo effect on neuromuscular transmission of thymopoietin, a putative thymic hormone which induces the expression of Thy-1 on cultured prothymocytes. The possible function of an antigen shared by developing muscle and thymocytes, T lymphocytes and brain is open to speculation.

Original languageEnglish (US)
Pages (from-to)163-165
Number of pages3
Issue number5616
StatePublished - 1977
Externally publishedYes


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