Biology Reference
In-Depth Information
The concentration of JH in the hemolymph is regulated not only by its
biosynthesis but also by its degradation, secretion, sequestration, etc. It is
thought that synthesis is the most important among these regulated processes
(
Gilbert, Granger, & Roe, 2000
). Much progress has been made in the past
25 years in understanding the regulation of JH biosynthesis by various
factors; peptide hormones such as allatotropins (ATs) and allatostatins (ASTs)
(
Stay & Tobe, 2007; Weaver & Audsley, 2009
), neurotransmitters (see review,
Goodman & Granger, 2005
), cAMP (
Granger et al., 1994
), and ecdysteroids
(
Gu & Chow, 1996; Kaneko, Kinjoh, Kiuchi, & Hiruma, 2011; Whisenton,
Bowen, Granger, Gilbert, & Bollenbacher, 1985; Whisenton, Watsona,
Granger, & Bollenbacher, 1987
) are all regulators of JH biosynthesis (see
reviews,
Goodman & Granger, 2005; Stay & Tobe, 2007
). Most studies of
JH-regulatory peptides, however, have concentrated on the gene structures
of the peptides, and their actions have been studied on relatively few different
developmental stages and different insect species. The stage-specific regulatory
mechanisms and roles of these factors on JH synthesis in relation to growth,
molting, and metamorphosis are as yet poorly understood.
Studies on JH lag far behind in those on ecdysteroids, which is mainly
due to the minute size of the CA and the “sticky” chemical nature of
JHs, which make experimental manipulation and measurement of these hor-
mones challenging. The sesquiterpenoid nature of these hormones, which
are not found in mammals, also makes it hard to incorporate knowledge
from other better-studied organisms. Moreover, the effects of JH on one
of the most prominent model insects,
Drosophila melanogaster
, are less easily
monitored than those on other insect groups such as lepidopterans.
For these reasons, it is helpful to study JH and its actions in a well-studied
lepidopteran model in which JH has strong, clear effects. The silkworm
B. mori
is suitable for this, genome information having been available for
some time (
The International Silkworm Genome Consortium, 2008
).
The various biological actions of JH have also been well studied, so that
Bombyx
allows us to study JH action at the molecular level much more easily
than in other non-
Drosophila
insect species. This chapter summarizes the
regulatory mechanisms of JH biosynthesis by three major factors,
ecdysteroids, catecholamines, and peptides, during molting and metamor-
phosis mainly in
Bombyx
larvae as a model case. The precise stage-specific
regulation of JH synthesis is shown to be achieved by the coordinated action
of several factors, which activate or inactivate JH synthesis in different ways
at different life stages, so that JH synthesis is properly adjusted to allow pro-
gress through the normal life cycle. In addition, we briefly describe how JH
