The prothoracic glands, source of the molting hormone ecdysone, regress within a few days after the final molt, a process which was analyzed with electron microscopic methods in the cockroaches Leucophaea and Blaberus. This strictly timed event is accompanied by drastic alterations in cellular fine structure. Early signs of breakdown appear in groups of nuclei whose substance becomes segregated into patches of contrasting electron density characteristic of pyknosis.
The most conspicuous change in the cytoplasm of parenchymal cells concerns the appearance of large, heterogeneous inclusion bodies in which various cellular elements become segregated. These compartments seem to represent autophagic vacuoles within which the gradual degradation of much of their contents takes place, presumably under the influence of lysosomal enzymes. Undigested swirls of membranous character may remain sequestered within these packets for some time.
At advanced stages of cellular atrophy, plasma membranes and nuclear envelopes have gradually disappeared, and masses of protoplasm undergoing autolysis become invaded by a greater number of hemocytes than are present in nymphal glands. These phagocytic elements appear to engulf debris of parenchymal cells as well as some degenerating connective tissue elements. After the completion of the regressive process, the axial band of musculature characteristic of the nymphal gland persists on its own. Whether or not some parenchymal cells (or possibly their precursors) capable of reactivation persist in the proximity of this muscle is unknown.
The resorption of the prothoracic gland in the newly emerged insect is the result of physiological autolysis and seems to be aided by the activity of phagocytic hemocytes.
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Dedicated to Professor W. Bargmann on his 60th birthday in friendship and admiration.
This study was supported by Research Grants AM-03984, NB-02145 and NB-05219 from the U.S.P.H.S.
I wish to express my thanks to Mrs. S. Wurzelmann, Mrs. C. Jones, Mrs. C. Grubman, and Mr. S. Brown for their excellent technical assistance.
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Scharrer, B. Ultrastructural study of the regressing prothoracic glands of blattarian insects. Z.Zellforsch 69, 1–21 (1966). https://doi.org/10.1007/BF00406264
- Parenchymal Cell
- Autophagic Vacuole
- Electron Microscopic Method