High impact information on MRF4

• In adult frogs, MRF4 RNA is detectable only in skeletal muscle (whereas MyoD, unexpectedly, is also expressed at low levels in the heart) [1].
• This implies that MRF4 is not involved in the commitment or early differentiation of muscle cells [1].
• During embryonic development, MRF4 RNA appears later than MyoD, at a time when the embryonic musculature already shows many differentiated features [1].
• A Xenopus MRF4 cDNA has been isolated and encodes an amino acid sequence with 72% identity to rat MRF4 [1].
• In Xenopus, previous studies showed that the transcripts of the myogenic regulatory factor (MRF) MRF4 accumulate during skeletal muscle differentiation, but nothing is known about the accumulation of XMRF4 protein during myogenesis [2].

Biological context of MRF4

• These results fail to support the hypothesis that MRF4 gene expression is triggered or is significantly up-regulated in myogenic cells by signals from motor axons [3].
• This suggests that MRF4 expression may be induced by innervation and hence may be involved in mediating transcriptional responses to innervation and that myogenin expression may compensate for the down-regulation of MRF4 gene [4].
• The up-regulation of myogenin by denervation suggests that myogenin expression may compensate for the down-regulation of MRF4 gene [5].

Anatomical context of MRF4

• MRF4 mRNA was detected later, just before the young myotube stage, and was strongly expressed during the different stages of the maturation of myotubes [6].

Associations of MRF4 with chemical compounds

• RT-PCR demonstrated similar MRF4 transcript levels in the aneural muscles and controls [3].

Analytical, diagnostic and therapeutic context of MRF4

• Consistent with this possibility, the level of Xenopus MRF4, but not MyoD, RNA is reduced in response to denervation of adult frog muscle [1].
• Muscle denervation persistently reduces the levels of MRF4 transcripts as early as the first stages of regeneration, whereas the levels of myogenin mRNA were increased in the late stages of regeneration [4].
• In adult Xenopus laevis, we analyzed, using reverse transcriptase-polymerase chain reaction (RT-PCR) and in situ hybridization, the influence of long-term muscle denervation on the accumulation of MRF4 and myogenin transcripts [5].

References