Stretch-induced growth in XXXX wing muscles: role of soluble growth-promoting factors.

@entity1184 @entity908 @entity1573 @entity35 @entity121
The involvement of soluble growth-promoting factors in stretch-induced @entity1184 of the @entity121 ( @entity121 ) in the @entity1573 wing was investigated. Soluble extracts were prepared from young @entity1573 @entity121 muscles made @entity1184 by passive stretch and from unstretched contralateral controls. Extracts were tested for their ability to stimulate cell proliferation and @entity908 phosphokinase (CPK) activity in primary monolayer cultures of @entity1573 embryo muscle cells. Factors were present in muscle extracts which showed a dose-dependent stimulation of cell proliferation and CPK activity in vitro. Passive stretch for 5 days produced a rapid @entity1184 of the @entity121 which was accompanied by a dramatic increase in the activity of the growth factor(s). Release of stretch resulted in an arrest of growth and an immediate fall in growth factor activity. The difference in growth-stimulating activity between control and stretched @entity121 extracts could be demonstrated in @entity1573 transferrin-sensitive @entity1573 myoblast cultures. Stretch thus induces an increase in a class-specific growth factor, possibly Transferrin, in the @entity121 . Stretched @entity121 extracts stimulated: (a) @entity1573 myoblast proliferation to a greater extent than an optimum concentration of @entity1573 embryo extract, and (b) CPK activity in vitro to a greater extent than excess Transferrin. Both control and stretched @entity121 extracts supported the growth of @entity35 myoblasts. We conclude that @entity121 muscle extracts also contain unknown growth factor(s) which are different from Transferrin.
