title: An in vitro study on regulation of prothoracic gland activity in the early last-larval instar of the silkworm Bombyx mori.
abstract: The endocrine mechanisms that regulate prothoracic gland (PG) activity in early stages of final larval instar of the silkworm Bombyx mori were investigated using a newly developed long-term cultivation system of the gland. The PGs dissected from day-0 fifth instar larvae did not secrete detectable amounts of ecdysone for the first 24 h in culture but started secretion within the next 2 days. The amount of secreted ecdysone increased day by day. When day-0 PGs were co-cultivated with corpora allata, however, they remained inactive for at least 8 days. PGs dissected from 1-day younger larvae (day-3 fourth instar larvae) secreted ecdysone for the first 24 h but stopped secretion for the next 24 h, followed by recovery of ecdysone secretory activity. By contrast, PGs from day-1 fourth instar larvae remained active throughout a cultivation period without any sign of inactivation. However, when the same glands were exposed to a high titer of 20-hydroxyecdysone for the second 24h in culture, they gradually lost their activity. These results indicate that PGs of fourth instar larvae are inactivated by ecdysteroid through a negative feedback mechanism and that thus inactivated PGs spontaneously recover ecdysone secretory activity in the early fifth instar unless inhibited by juvenile hormone.
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan. mizoguch@bio.nagoya-u.ac.jp
authors.forename: Akira
authors.initials: A
authors.lastname: Mizoguchi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kataoka
mesh_terms: D000818:Animals; D012831:Bombyx / Q000254:growth & development* / Q000378:metabolism*; D004440:Ecdysone / Q000378:metabolism*; D007301:Insect Hormones / Q000378:metabolism*; D007605:Juvenile Hormones / Q000378:metabolism*; D007814:Larva / Q000502:physiology; D008297:Male; D009924:Organ Culture Techniques
chemical_list: D007301:Insect Hormones; D007605:Juvenile Hormones; D004440:Ecdysone; C009089:prothoracicotropic hormone