The role of 20-hydroxyecdysone in stimulating DNA synthesis in corpora allata of the silkworm, Bombyx mori.
Temporal changes in DNA synthesis were examined in the corpora allata of the silkworm Bombyx mori during the penultimate larval stadium. 5'-Bromo-2'-deoxyuridine (BrdU) labeling revealed that allatal DNA synthesis rose early in the stadium, peaking at about 2% of corpus allatum (CA) cells 24 hr after ecdysis. This corresponded to a rising phase of the ecdysteroid titer reported previously. DNA synthesis declined to a nearly undetectable level 1 day later. In larvae fed on leaves coated with 20-hydroxyecdysone (20E), the number of BrdU-labeled cells increased continuously after the normal peak and reached about 8% of CA cells at the end of the stadium. However, total count of CA cells from whole-mount monolayers and colchicine treatment indicated that, regardless of DNA content, CA cells did not divide. To determine if the rise in 20E was responsible for the onset of allatal DNA synthesis, we have established an organ culture system to support de novo DNA synthesis in vitro. The number of BrdU-labeled cells increased with increasing 20E concentration between 0.1 and 0.5 microg ml-1 in the medium, corresponding well to the rising 20E titer in the hemolymph. The level of DNA synthesis in culture was further elevated when 20% hemolymph was added together with 20E, suggesting that other direct stimulatory factors for allatal DNA synthesis may also exist in the hemolymph.
Chiang
A S
AS
Department of Life Science, National Tsing-Hua University, Taiwan, Hsinchu, 30043, Republic of China. lscas@life.nthu.edu.tw
Chen
S F
SF
Chang
L H
LH
D000818:Animals; D000963:Antimetabolites / Q000378:metabolism; D012831:Bombyx / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D001973:Bromodeoxyuridine / Q000378:metabolism; D002452:Cell Count; D003335:Corpora Allata / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D004247:DNA / Q000096:biosynthesis* / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004441:Ecdysterone / Q000494:pharmacology*; D006458:Hemolymph / Q000502:physiology; D018978:Molting / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors
D000963:Antimetabolites; D004441:Ecdysterone; D004247:DNA; D001973:Bromodeoxyuridine