Table 1.

Summary of characteristics of embryonic, fetal, and adult myoblasts and myofibers.

	Culture appearance and clonogenicity	Signaling molecule response	Drug sensitivity	Myofiber morphology in culture
Embryonic myoblasts	Elongated, prone to differentiate and form small colonies, do not spontaneously contract in culture	Differentiation insensitive to TGFβ–1 or BMP4	Differentiation insensitive to phorbol esters (TPA), sensitive to merocynine 540	Mononucleated myofibers or myofibers with few nuclei
Fetal myoblasts	Triangular, proliferate (to limited extent) in response to growth factors, spontaneously contract in culture	Differentiation blocked by TGFβ–1 and BMP4	Differentiation sensitive to phorbol esters (TPA)	Large, multinucleated myofibers
Satellite cells/Adult myoblasts	Round, clonogenic, but undergo senescence after a limited number of passages, spontaneously contract in culture	Differentiation blocked by TGFβ–1 and BMP4	Differentiation sensitive to phorbol esters (TPA)	Large, multinucleated myofibers

	MyHCemb	MyHCperi	MyHCI	MyHCIIa	MyHCIIx	MyHCIIb
Embryonic myofibers	+	−	+	−	−	−
Fetal myofibers	+	+	+/−	+/−	+/−	+/−
Adult myofibers	−	−	−	+	+	+

All from Biressi (2007b) or review of Biressi et al. (2007a).

Derived from (Agbulut et al., 2003; Gunning and Hardeman, 1991; Lu et al., 1999; Rubinstein and Kelly, 2004; Schiaffino and Reggiani, 1996)