Nuclear domains in skeletal myotubes: the localization of transferrin receptor mRNA is independent of its half-life and restricted by binding to ribosomes.
The retention of mRNAs near the nuclei that synthesize them may be an important feature of the organization of multinucleated skeletal myotubes. Here, we assess the possible role of two factors in this localization. First, we examine the role of mRNA half-life, by studying the distribution of the mRNA for the transferrin receptor (TfR), whose half-life can be manipulated in culture by changing the availability of iron. In situ hybridization of myotubes of the mouse muscle cell line C2 shows that TfR mRNA is concentrated in the core of the myotubes. Its distribution around the nuclei is often asymmetric and its concentration changes abruptly. Stable transcripts display the same asymmetric localization as unstable ones, suggesting that half-life does not determine subcellular localization of TfR mRNA. Differential effects of the protein synthesis inhibitors puromycin and cycloheximide suggest that the mRNA is retained in position by its association with ribosomes. We then examine the distribution of the rough endoplasmic reticulum (RER) and find it to be broader than the distribution of TfR mRNA. In contrast to TfR mRNA, the mRNA for a secreted immunoglobulin kappa light chain has a more uniform distribution. Taken together, the results suggest that TfR mRNA may associate with RER subdomains by specific targeting.
Ralston
E
E
Laboratory of Neurobiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-4062, USA. esr@codon.nih.gov
McLaren
R S
RS
Horowitz
J A
JA
D000818:Animals; D002451:Cell Compartmentation; D002460:Cell Line; D002467:Cell Nucleus / Q000648:ultrastructure; D003513:Cycloheximide / Q000494:pharmacology; D018870:Endoplasmic Reticulum, Rough / Q000648:ultrastructure; D006207:Half-Life; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000378:metabolism / Q000648:ultrastructure*; D018482:Muscle, Skeletal / Q000378:metabolism / Q000648:ultrastructure*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011691:Puromycin / Q000494:pharmacology; D012333:RNA, Messenger / Q000302:isolation & purification*; D011990:Receptors, Transferrin / Q000302:isolation & purification*; D012270:Ribosomes / Q000378:metabolism
D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D011990:Receptors, Transferrin; D011691:Puromycin; D003513:Cycloheximide