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Horodyski, 2006 ). Nutritional effects in insects are mediated by insulin sig-
naling ( Britton, Lockwood, Li, Cohen, & Edgar, 2002 ), and these observa-
tions suggest involvement of the insulin signaling pathway in the control of
JH synthesis. In the insulin receptor mutant ( InR )in Drosophila , JH synthesis
is reduced compared to wild-type flies ( Tatar et al., 2001; Tu, Yin, & Tatar,
2005 ), an effect that is due to decreased HMGR expression ( Belgacem &
Martin, 2007 ). Since insulin causes the reduction of sNPF expression in
Drosophila ( Root et al., 2011 ), and considering that sNPF also reduces
HMGR expression in Bombyx , the reduced JH synthesis seen in InR flies
is probably due to the upregulation of sNPF, so that HMGR expression
is suppressed followed by the decrease in JH synthesis. In addition, the target
of rapamycin pathway also regulates the expression of both HMGR and
HMGS in the cockroach, Blattella germanica , and this pathway is involved
in the control of JH biosynthesis in that insect ( Maestro et al., 2009 ).
3. MOLECULAR ACTIONOF JH ON INSECT MOLTING AND
METAMORPHOSIS
Studies of the action of JH at the molecular level have been hampered
due to, in particular, the marked tendency of the hormone to bind to sur-
faces, but notable advances have been made in the last few years; the most
important results have been summarized by Riddiford (2008) . In this
review, we briefly discuss the most recent findings including the long-
awaited discovery of a JH receptor.
3.1. Methoprene-tolerant (Met) as a JH receptor
The methoprene - tolerant ( Met ) gene, first found in Drosophila , is a member of
the basic helix-loop-helix (bHLH)-Per-Arnt-Sim (PAS) family of tran-
scriptional regulators ( Ashok, Turner, & Wilson, 1998 ). Met null mutants
are resistant to the morphogenetic effect of the JH analog methoprene
and are viable, although their fecundity is reduced ( Wilson & Ashok,
1998 ). JH is necessary for egg maturation so that yolk protein uptake is con-
trolled ( Soller, Bownes, & Kubli, 1999 ); therefore, it has been long thought
that the Met protein is involved in the JH signaling pathway. In Drosophila ,
germ cell - expressed ( gce ) is known as a paralog of Met ( Godlewski, Wang, &
Wilson, 2006 ), but only Met has been found in non- Drosophila insects
( Charles et al., 2011; Wang, Baumann, & Wilson, 2007 ). In non- Drosophila
insects such as Tribolium , knockout of Met RNA expression by the injection
of dsRNA caused precocious metamorphosis, and those individuals are
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