Steroid control of muscle remodeling during metamorphosis in Manduca sexta

Abstract

During metamorphosis in the tobacco hornworm, Manduca sexta, the abdominal body-wall muscle DEO1 is remodeled to form the adult muscle DE5. The degeneration of muscle DEO1 involves the dismantling of its contractile apparatus followed by the degeneration of muscle nuclei. As some nuclei are degenerating, others begin to incorporate 5-bromodeoxyuridine (BrdU), indicating the onset of nuclear proliferation. This proliferation is initially most evident at the site where the motoneuron contacts the muscle remnant. The developmental events involved in muscle remodeling are under the control of the steroid hormones, the ecdysteroids. The loss of the contractile elements of the larval muscle requires the rise and fall of the prepupal peak of ecdysteroids, whereas the subsequent loss of muscle nuclei is influenced by the slight rise in ecdysteroids seen after pupal ecdysis. Incorporation of BrdU by muscle nuclei depends on both the adult peak of the ecdysteroids and contact with the motoneuron. Unilateral axotomy blocks proliferation within the rudiment, but it does not block its subsequent differentiation into a very thin muscle in the adult.

Morphological and functional maturation of a skeletal muscle regulated by juvenile hormone

“…These events are mainly regulated by 20-HE in the absence of JH (Weeks and Truman, 1985;Schwarz and Truman, 1983;Luedemann and Levine, 1996;Hegstrom and Truman, 1996; reviewed in Weeks and Truman, 1986). The importance of metamorphosis for flight muscle differentiation and development has been shown by manipulating the levels of JH.…”

Hormonal control of ventral diaphragm myogenesis during metamorphosis of the moth, Manduca sexta

“…The most extensively studied of these larval muscles is DEO1, which is remodeled to form the DE5 muscle of the adult (Hegstrom and Truman 1996a). As DEO1 is remodeled, the birefrigence of the larval muscle is lost on day P+2 and BUdR incorporation begins in the forming anlage 1 day later (Hegstrom and Truman 1996a).…”

“…The most extensively studied of these larval muscles is DEO1, which is remodeled to form the DE5 muscle of the adult (Hegstrom and Truman 1996a). As DEO1 is remodeled, the birefrigence of the larval muscle is lost on day P+2 and BUdR incorporation begins in the forming anlage 1 day later (Hegstrom and Truman 1996a). BUdR incorporation reaches a maximum between P+5 and P+7 days and then declines as the adult muscle starts showing birefringence on day P+9 (Hegstrom and Truman 1996a).…”

“…As DEO1 is remodeled, the birefrigence of the larval muscle is lost on day P+2 and BUdR incorporation begins in the forming anlage 1 day later (Hegstrom and Truman 1996a). BUdR incorporation reaches a maximum between P+5 and P+7 days and then declines as the adult muscle starts showing birefringence on day P+9 (Hegstrom and Truman 1996a). During the proliferative phase the width of the growing anlage begins increasing on day P+6, and the insertion angle changes between P+7 and P+8 days as the anterior portion of the anlage migrates across the epidermis to achieve its adult attachment site (Truman and Reiss 1995).…”

“…Adult-specific muscles are formed later during metamorphosis. Some of the adult-specific muscles are formed by the remodeling of larval muscles (Hegstrom and Truman 1996a) while others are formed by proliferation and subsequent differentiation of adult-specific myoblasts during late larval and early pupal stages (Bate et al 1991;Consoulas et al 1997). We report that either the proliferation or differentiation of adult-specific myoblasts of the ventral diaphragm are stimulated by the ecdysteroid, 20-hydroxyecdysone (20E), the type of response being dependent on the concentration of 20E to which the cells are exposed.…”