Biology Reference
In-Depth Information
2.4. Regulation by peptide hormones
JH biosynthetic activity by the CA can only be measured
in vitro
; the extent
of JH synthesis depends on how this is assayed
in vitro
. When a
brain-CC-CA complex is dissected intact and its JH synthetic activity is
measured
in vitro
, the amount of JH produced by the CA in each stage is
lower than would be the case without the brain (
Fig. 3.3
A). The JH syn-
thetic activity of the CA alone is approximately doubled compared to the
intact brain-CC-CA, but the pattern of JH synthesis during development
is similar to that of the brain-CC-CA complex. Although the CC-CA
complex without the brain produces a similar amount of JH to the CA alone,
the fluctuating pattern of JH synthetic activity is distinct; there are two
periods of depressed synthetic activity: on day 3 of the fourth larval stage
and again on day 0 of the fifth stage just after the final larval ecdysis
(
Fig. 3.3
A). JH synthetic activity by the CC-CA complex in the fourth
instar stadium thus parallels the JH titer in the hemolymph, although syn-
thesis is (as expected) shifted forward by several hours (
Niimi & Sakurai,
1997
;
Fig. 3.1
B); therefore, several factors supplied by the cephalic organs
regulate JH synthesis under
in vivo
conditions.
Recent studies show that many kinds of peptides can stimulate or inhibit
JH production by the CA (
Goodman & Granger, 2005
), but most of these
studies concern the isolation, characterization, and distribution of these
peptides (
Stay & Tobe, 2007; Weaver & Audsley, 2009
). In this section,
we concentrate on four peptides, short neuropeptide F (sNPF), AT, AST,
and ecdysis triggering hormone (ETH), and discuss how these peptides co-
operate to stimulate and/or suppress JH synthesis in stage-specific manners.
2.4.1 sNPF suppresses JH biosynthesis in a stage-specific fashion
sNPF is a short peptide [(A/L)R(P/L)RFamide] present in
Bombyx
for
which the mRNA is expressed primarily in the CC and a small amount
in the brain; the translated peptide in the CC is transferred to the CA
through nerve axons to suppress JH synthesis in early last stage larvae
(
Yamanaka et al., 2008
). Detailed analysis of the action of sNPF showed that
its inhibitory action on the CA was effective only from the day 3 fourth
instar and in early fifth stage larvae just after the last larval ecdysis; these
are the stages when CC-CA complexes produce a smaller amount of JH
in vitro
than that is produced by the CA alone (
Fig. 3.3
A). The two depres-
sions of the JH synthesis by the CC-CA complexes at these times are most
likely due to the release of sNPF from the CC where this peptide is