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synthesized. Although the fluctuation of sNPF in the hemolymph is un-
known, mRNA levels of sNPF in the CC are relatively high with some fluc-
tuations during the fourth instar and in the feeding stage of the fifth instar
stadium (
Hiruma, Kaneko, & Kinjoh, 2010
; unpublished data).
There are two isoforms of sNPF receptors: isoform 1 (
BNGR-A10
) and
isoform 2 (
BNGR-A11
)(
Yamanaka et al., 2008
) both are expressed in the
CA. Receptor mRNA levels in the CA, in particular of isoform 1, become
high on days 2-3 of the fourth larval stage, just when sNPF is effective in
inhibiting the JH synthesis, but decline sharply at the time (day 3 of the
fourth larval stage) when suppressive action of sNPF disappears. This indi-
cates that the pattern of sNPF receptor expression is one of the factors that
causes JH biosynthesis suppression by sNPF to be stage specific, at least in the
fourth larval stage.
In vitro
CA culture experiments with 20E suppress recep-
tor mRNA levels and indicate that the premolting surge of ecdysteroid is
among the factors regulating receptor levels. In addition, insulin also
suppressed
sNPF
receptor expression at this time (unpublished data). Similar
downregulation of the
sNPF
receptor by insulin signaling has also been
found in
Drosophila
odorant receptor neurons (
Root, Ko, Jafari, & Wang,
2011
). It will be necessary to measure insulin concentration in the hemo-
lymph to establish whether or not insulin functions to regulate sNPF recep-
tor levels
in vivo
.
Thus, the suppressive action of sNPF on JH synthesis after the final larval
ecdysis also contributes, in addition to the actions of ecdysteroid and dopa-
mine (see above), to the cessation of JH synthesis that is required for the
initiation of metamorphosis (
Figs. 3.3
A and
3.4
).
2.4.2 AT is a regulator for sNPF expression
ATwas the first peptide to be isolated that affects JH synthesis by the CA, but
the allatotropic action of AT evidently does not extend to insects from other
families. AT only activates the CA of female adult
Manduca
, the CA of other
insects being unaffected (
Kataoka et al., 1989
). We have attempted to elu-
cidate the strange function of this tridecapeptide using another Sphingid
moth,
Agrius convolvuli
, a relative of
Manudca
[
Agrius
AT is identical to that
of
Manduca
(H. Kataoka, personal communication)]. We found that AT did
activate JH synthesis by the CA from adult female
A. convolvuli in vitro
, but
this was only seen when we increased the temperature to 30
C, which was
the temperature that the original paper reported, from 25
C(
Fig. 3.3
B). AT
did not activate the CA from other stages or from males of
Agrius
even at