ISSN:
0362-2525
Keywords:
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Medicine
Notes:
In studying ultrastructural changes in metamorphosis-related degeneration of intersegmental muscles in Antheraea polyphemus, particular attention was directed to the mechanisms and timing of degradation of organelles and myofilaments. At emergence, the muscles are typical slowly contracting insect muscles, with a few dense body lysosomes and occasional autophagic vacuoles containing mitochondria. During the early phases of degradation the number of autophagic vacuoles, dense bodies, and lamellar bodies increases rapidly, along with an expansion of the Golgi system and the T system. Free glycogen particles and glycogenosomes are demonstrated by the PATAg test.Between 7 and 20 hours after ecdysis the T system continues to expand, the fibers subdivide, and the contractile system is degraded. Myofibrils fragment; myofilaments are not enclosed in isolating membranes at the time of their dissolution. The destruction of individual filaments occurs rapidly, with few intermediate stages being seen, while thick filaments tend to disappear earlier than thin filaments and Z-line material. The process is generalized and not confined to specific regions of the fiber. Autophagy destroys cell organelles in apparent synchrony with the first signs of nuclear pycnosis.By 20 to 30 hours after emergence, the fibers are reduced to lamellae of polynucleate sarcoplasm containing no organized contractile material. The sarcoplasm is filled with autophagic vacuoles containing mitochondria, dense lamellar or residual bodies, and ribosome-rich sarcoplasm. The number of mitochondria is drastically reduced at this time.In the final phases of involution (40-49 hours after emergence) shedding of the residual sarcoplasm precedes the expulsion of the pycnotic nuclei into the hemocoele.These results indicate that autophagy is responsible for the selective destruction of mitochondria, glycogen particles, ribosomes, and other organized sarcoplasmic structures. The one exception is the dissolution of the myofilaments, a process which remains undefined but which appears to be independent of lysosomal activity.
Additional Material:
1 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jmor.1051540104
