Density-dependent arrest of DNA replication is accompanied by decreased levels of c-myc mRNA in myogenic but not in differentiation-defective myoblasts
✍ Scribed by Thomas Sejersen; Janos Sümegi; Nils R. Ringertz
- Book ID
- 102881536
- Publisher
- John Wiley and Sons
- Year
- 1985
- Tongue
- English
- Weight
- 771 KB
- Volume
- 125
- Category
- Article
- ISSN
- 0021-9541
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✦ Synopsis
Myoblasts from primary rat cultures and established mouse (CIIO) and rat (L6, Arna 420) cell lines were examined for c-oncogene expression during exponential growth and under conditions which allowed myogenic differentiation. The abundance of c-Ki-ras transcripts in mRNA from confluent, quiescent cultures was reduced to 15-40% of that in rnRNA from exponentially growing cells. This reduction was found both in primary myoblast cultures, myoblast lines that formed rnyotubes (L6 and C110) and in a differentiation defective subline (Arna 420). The level of c-rnyc transcripts was lowered when rnyogenic rat L6 rnyoblasts reached a high cell density, stopped DNA synthesis and formed myotubes. At the same cell density, growth arrested myoblasts of differentiation defective Arna 420 cells maintained a high level of c-myc expression. This shows that DNA replication and c-rnyc expression are independently regulated. All rnyoblast lines also showed expression of c-abl during exponential growth phase. Reduced expression was seen in differentiated L6 and CllO cultures. No expression was detected when rnRNA from rnultiplying and differentiating myoblasts cultures were probed for c-rnyb, c-erbA, c-erbB, c-mos, c-fes, and c-src. The observations are consistent with a role for c-Ki-ras in rnyoblast proliferation and suggest that a reduction in c-rnyc expression may be a necessary prerequisite for terminal myogenic differentiation. 1982).