Printed in Great Britain © The Company of Biologists Limited 1986 The preliminary characterization of mitogens secreted by embryonic chick wing bud tissues in vitro

Embryonic chick wing bud tissues secrete diffusible mitogens when cultured in vitro (Bell & McLachlan, 1985). These molecules may play an important role in limb development since media conditioned by morphogenetically active regions of the wing bud possess greater mitogenic activity than media conditioned by non-morphogenetic regions. These studies show that while the chick-derived growth factors were mitogenic for mouse-derived NIH 3T3,10T1/2 and NR6 cells and chick limb bud cells, they did not stimulate DNA synthesis in 3B11, PC13 END, normal rat kidney or bovine endothelial cells. Furthermore, the effects of the chick-derived mitogens were synergistically enhanced by insulin and PGF ^ but remained unaffected by ECDGF, EGF, FGF and MSA. These findings indicate that embryonic chick limb bud cells synthesize and secrete growth factors which resemble in function other well-characterized growth factors and in particular PDGF