Fig. 5. Fyn mediates Sca-1 function in myogenesis. (A) Fyn and Src kinase activities were measured in wild-type C2C12 cells (C; white bars) and cells expressing Sca-1 antisense (AS; gray bars). Cells grown in differentiation media for 2 and 5 days demonstrated an appropriate increase in Fyn activity in control and antisense-expressing cells at day 5 (top), low levels of Src activity at all time points (bottom), and an inappropriate increase in Fyn activity at day 2 in cells expressing Sca-1 antisense (top). Data shown are mean±s.e.m. (n=3; ^*significant difference, P<0.05). Pro, proliferating cells. (B) Control (solid white or grey) or mutant-expressing plasmids (hashed bars), both co-expressing GFP, were transfected into Sca-1 antisense (AS) or wild-type C2C12 (C) cells. Cells were grown in differentiation media for 5 days. The ratio of GFP-expressing (i.e. transfected) mononuclear cells:myotubes (2 nuclei) was lower in antisense cells (AS) transfected with dominant-negative Fyn-K299M compared with antisense cells transfected with control plasmid expressing GFP alone (GFP), and higher in wild-type (C) cells transfected with constitutively active Fyn-Y531F compared with GFP-transfected wild-type cells. Data shown are mean±s.e.m. (n=3; ^*significant difference, P<0.05).