A novel monoclonal antibody identifies all avian embryonic myogenic cells and adult smooth muscle cells

A novel monoclonal antibody, designated GIIF3, recognized prospective and d ifferentiated smooth muscle cells in avian species studied - guinea fowl, c hicken and quail. The GIIF3 antigen appeared in the myocardial, and the myo tomal cells of the embryos at Hamburger-Hamilton stages 10 and 14, respecti vely. The expression of the GIIF3 molecule in the vascular smooth muscle ce lls emerged in the ventral wall of the dorsal aorta at Hamburger-Hamilton s tage 16. The visceral smooth muscle cells started to produce the GIIF3 mole cule from Hamburger-Hamilton stage 28 onwards. In both cardiac and skeletal muscles the GIIF3 expression gradually diminished, and it was lost by the end of the embryonic period, unlike in the differentiated vascular and visc eral smooth muscle cells. In the latter cells the GIIF3 immunoreactive prod uct showed a fine granular pattern that accumulated in the central region o f the cytoplasm; it also occurred in the nucleus. A heavily stained discont inuous layer was associated with the cell membrane. The immunoblotting of t he GIIF3 antibody recognized protein bands at 50 and 42 kDa in lysates of a dult avian gizzard. A detailed comparative immunohistochemical study was ma de by smooth muscle markers, which confirmed the results of the immunoblott ing, namely, that the GIIF3 monoclonal antibody recognized an avian myogeni c cell specific molecule. During smooth muscle cell differentiation the GII F3 molecule appeared as early as the a-smooth muscle actin, and in adult bi rds continued to be expressed; therefore the GIIF3 molecule could be regard ed as a novel avian smooth muscle specific marker.