Skeletal muscle myofibrillogenesis as revealed with a monoclonal antibody to titin in combination with detection of the alpha- and gamma-isoforms of actin.
The distribution of titin during myofibrillogenesis was examined using rat skeletal muscle myogenic cultures and fluorescent-antibody staining. Efforts were made to compare the distribution and temporal sequence of incorporation of titin relative to that of the alpha- and gamma-isoforms of actin. The present observations suggested the following sequence of titin assembly: (1) newly synthesized titin molecules are distributed in a diffuse pattern throughout the sarcoplasm, (2) the titin molecules gradually associate with alpha- and gamma-actin-positive stress fiber-like structures (SFLS), (3) groups of titin molecules begin to segregate on the SFLS, and (4) titin molecules align in a mature doublet configuration in the sarcomeres of nascent myofibrils. Titin assembly on the SFLS often appeared prior to the onset of either alpha- or gamma-actin periodicity on nascent myofibrils; the latter result suggested a role for titin in sarcomeric organization. Actin distribution on SFLS and its periodicity on nascent myofibrils was usually identical between the alpha- and gamma-isoforms. This suggested that gamma-actin participated in myofibrillogenesis in a manner indistinguishable from that of alpha-actin. The transition seen from continuous actin staining of SFLS to the I-band staining pattern of mature myofibrils is discussed in relation to the corresponding reorganization of actin filaments and the molecular associations that this would entail.
Handel
S E
SE
Muscle Biology Laboratory, University of Wisconsin, Madison 53706.
Wang
S M
SM
Greaser
M L
ML
Schultz
E
E
Bulinski
J C
JC
Lessard
J L
JL
D000199:Actins / Q000276:immunology / Q000502:physiology*; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D002478:Cells, Cultured; D064211:Connectin; D005455:Fluorescent Antibody Technique; D066298:In Vitro Techniques; D009024:Morphogenesis; D009124:Muscle Proteins / Q000276:immunology / Q000502:physiology*; D009210:Myofibrils / Q000502:physiology*; D011494:Protein Kinases; D051381:Rats
D000199:Actins; D000911:Antibodies, Monoclonal; D064211:Connectin; D009124:Muscle Proteins; D011494:Protein Kinases