Myogenesis of striated muscle in vitro: Hormone and serum requirements for the development of glycogen synthetase in myotubes

✍ Scribed by Gabriel De La Haba; George W. Cooper; Virginia Elting

• Publisher: John Wiley and Sons
• Year: 1968
• Tongue: English
• Weight: 634 KB
• Volume: 72
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.1040720105

✦ Synopsis

The fusion in vitro of embryonic niyoblasts to form multinucleated myotubes requires the addition of serum to a basal nutrient medium. The serum requirement for fusion can be satisfied by insulin with somatotropin potentiating its effect. Myotubes formed under these conditions fail to differentiate to cross-striated, spontaneously contractile muscle fibers. This arrest of develorment is reversible if serum is restored to the medium.

Development of the enzyme glycogen synthetase was studied as an additional indicator of muscle differentiation. In cultures developing i n the presence of serum, this enzyme was demonstrated by autoradiography to be highly concentrated in myotubes as compared to mononuclear cells. The activity of the enzyme remains low in (1) cultures formed in response to insulin and somatotropin in the absence of serum, as well as ( 2 ) in cultures formed in unsupplemented basal medium which are virtually lacking i n myotubes. The addition of serum to (1) restores the development of this enzyme. Serum which has been extensively digested with the proteolytic preparation, pronase, and subjected to boiling temperature, when combined with insulin and somatotropin is also capable of promoting the development of glycogen synthetase to a specific activity which exceeds the control. The serum factor is not lost on exhaustive dialysis, nor can enzyme promoting activity be liberated by heat denaturation of serum proteins.