Transitory expression of Thy-1 antigen in skeletal muscle development

A CELL surface differentiation antigen known as Thy-1 (formerly called theta¹) is expressed during development of brain and thymocytes in both rat and mouse (see ref. 2 for review). 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 vitro³ and mouse Thy-1 has been reported on epidermal cells (see ref. 2 for review) and a mammary tumour⁴. The Thy-1 antigen has been reported lacking in other adult tissues, including muscle¹. We present here evidence for an antigen with the serological 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.