Biology Reference
In-Depth Information
Another candidate for JH regulation is prothoracicotropic hormone
(PTTH) which stimulates PGs to secrete ecdysteroid. This peptide is pro-
duced by brain neurosecretory cells and is released into the hemolymph
from the CA in lepidopterans, so that PTTH might also affect JH synthesis,
but our study showed little effect of this nature (unpublished data).
Ecdysteroid is known to have a feedback action, both positively and neg-
atively, on its own synthetic organ, the prothoracic gland (
Sakurai, 2005
).
It has been suggested that JH too might have feedback loops (
Goodman &
Granger, 2005
). However, when CA of day 1 fourth instar larvae were
cultured with or without 0.01 or 1
m
g/ml methoprene for 8 h, JH synthesis
was little affected. In addition, when we cultured CC-CA complexes from
day 0 fifth instar
Bombyx
larvae with 100
m
M pravastatin, a derivative com-
pound of a competitive inhibitor of HMGR, compactin (
Endo, Kuroda,
& Tanzawa, 1976
) for 24 h, JH biosynthesis was completely shut down,
but the expression of none of the JH synthetic enzymes in the CA, including
HMGR itself, was affected (Kinjoh, Kaneko, & Hiruma, unpublished data).
Therefore, there is little evidence of the presence of feedback regulation of JH
synthesis by JH both at the level of JH synthesis and at the JH synthetic
enzymes.
Finally, a JH receptor has been found, and cumulative information on
the JH signaling pathway has increased tremendously during the past few
years; therefore, we can expect the components of the JH signaling network
to be fully described within the near future. This will allow fuller under-
standing of not only the cellular actions of JH in regulating metamorphosis
but also the interendocrine signaling that plays an important role in deter-
mining the timing of metamorphic developmental events.
ACKNOWLEDGMENTS
We thank Professor Stuart E. Reynolds for critically, and patiently, reading the manuscript.
This work was supported by grants from Japanese Society for the Promotion of Science
(23658044 and 22380032) and the Program for Promotion of Basic Research Activities
for Innovative Biosciences (PROBRAIN).
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Ashok, M., Turner, C., & Wilson, T. G. (1998). Insect juvenile hormone resistance gene
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