The Journal of Neuroscience, March 1, 1998, 18(5):1786-1794
Steroid and Neuronal Regulation of Ecdysone Receptor Expression
during Metamorphosis of Muscle in the Moth, Manduca
sexta
Carol D.
Hegstrom1,
Lynn M.
Riddiford2, and
James W.
Truman2
1 Department of Psychology, University of California,
Berkeley, California 94720-1650, and 2 Department of
Zoology, University of Washington, Seattle, Washington 98195-1800
Ecdysteroids regulate the remodeling of the dorsal external oblique
1 (DEO1) muscle during metamorphosis in Manduca sexta (). We show that the temporal and spatial patterning of the A and B1 isoforms of the ecdysone receptor (EcR) within muscle DEO1 corresponds with the developmental fates of the
fibers. Using antibodies directed to specific isoforms of EcR, we show
that the expression of various EcR isoforms in myonuclei differ among
the five fibers of DEO1 and correspond with the developmental response
of the muscle to the changing steroid titers and to the pattern of
innervation. Muscle degeneration and apoptosis of myonuclei in all
fibers are correlated with the expression of only EcR-A just before
pupal ecdysis and then with the expression of low levels of both EcR-A
and EcR-B1 shortly after pupation. Only the first fiber of muscle DEO1
participates in the regrowth of the adult muscle, and only this fiber
shows an upregulation of EcR-B1 that is evident at 3 d after pupal
ecdysis. Denervation of the muscle prevents both the upregulation of
EcR-B1 and myoblast proliferation. We conclude that the developmental
fate of muscle DEO1 during metamorphosis is orchestrated by
interactions between rising and falling ecdysteroid titers, the pattern
of expression of EcR isoforms by the muscle, and interactions with
other cells in the local environment.
Key words:
muscle; nuclear hormone receptor; ecdysteroid; metamorphosis; receptor isoform; steroid receptor
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