Distribution of the endoplasmic reticulum and its relationship with the sarcoplasmic reticulum in skeletal myofibers.
We have analyzed the distribution of the endoplasmic reticulum (ER) within isolated rat skeletal muscle flexor digitorum brevis myofibers. Studies with confocal microscopy indicated that the resident ER proteins displayed a perinuclear and cross-striated distribution that extended over the I band areas. Interestingly, two discrete distribution patterns were observed when different receptor or viral marker proteins were blocked in the ER. Accordingly, the vesicular stomatitis virus G protein that lost its efficient export through the Golgi apparatus during myogenesis preferentially marked the A-I junctional areas. The proteins that retained their Golgi processing after myogenesis, on the contrary, concentrated around the myonuclei and over the Z lines. Furthermore, the ER exit site marker sec23 located to Z lines but not to A-I junctions. To analyze the ultrastructural organization of the ER, we infected myofibers with recombinant virus expressing KDEL-tagged peroxidase that is translocated into the ER. With transmission electron microscopy, peroxidase activity was found in perinuclear and Z line-flanking tubular structures, but also within the terminal cisternae of the sarcoplasmic reticulum. The translocon-associated protein exhibited a similar localization. Taken together, the terminal cisternae contained unevenly distributed rough ER structures apparently lacking the export function. The exporting ER comprised perinuclear and Z line-flanking structures.
Kaisto
Tuula
T
Department of Anatomy and Cell Biology, University of Oulu, P.O. Box 5000, Fin-90014 University of Oulu, Finland.
Metsikkö
Kalervo
K
D000818:Animals; D002451:Cell Compartmentation / Q000502:physiology; D004721:Endoplasmic Reticulum / Q000378:metabolism / Q000648:ultrastructure*; D005260:Female; D005455:Fluorescent Antibody Technique; D006056:Golgi Apparatus / Q000378:metabolism / Q000648:ultrastructure; D008562:Membrane Glycoproteins / Q000378:metabolism; D008854:Microscopy, Electron; D018485:Muscle Fibers, Skeletal / Q000378:metabolism / Q000648:ultrastructure*; D018482:Muscle, Skeletal / Q000378:metabolism / Q000648:ultrastructure*; D017510:Protein Folding; D021381:Protein Transport / Q000502:physiology*; D011506:Proteins / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism / Q000648:ultrastructure*; D033921:Vesicular Transport Proteins; D014759:Viral Envelope Proteins / Q000378:metabolism
C028391:G protein, vesicular stomatitis virus; D008562:Membrane Glycoproteins; D011506:Proteins; D011993:Recombinant Fusion Proteins; C512740:Sec23a protein, rat; D033921:Vesicular Transport Proteins; D014759:Viral Envelope Proteins