M-type 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase is the productof a late muscle differentiation gene

Genes that are expressed in adult muscle, but not in myotubes, are useful m arkers of the last steps of muscle maturation. We have investigated at what stage of differentiation the muscle-specific (M) promoter of a gene that c odes for 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK2) become s functional. M-PFK2 mRNA, which is present in adult muscle, did not appear during differentiation of L6 myoblasts into myotubes induced by growth fac tor withdrawal and hormonal treatment, even when this differentiation was s timulated by expression of transgenes coding for myf-5 or Rb. A comparison with the expression pattern of muscle genes showed that M-PFK2 is a marker of mature skeletal muscle. We also found that M-PFK2 is expressed in both t ypes (slow-twitch and fast-twitch) of adult muscle. Thus, the M-PFK2 promot er is a novel model for studying the transcriptional control of the final s teps of muscle differentiation that are common to the two types of myofiber s. (C) 1999 Academic Press.