Insect Control: Biological and Synthetic Agents - Index of

M389
L308
M272
T304
T393
V404
L420
Q503
V384
V416
versions of the gene switch used only the EcR LBDs
and were 1000 times less sensitive than the gene
switch reported by Tavva et al. (2007a).
A4.1. Recent Progress on Mode of Action
of 20-Hydroxyecdysone and Non-
Steroidal Ecdysone Agonist Insecticides
Prior research on JH or its analogs (JHA) and 20-E
had assumed that these two growth and developmental
hormones have independent pathways and
targets for action. Grace Jones and her collaborators
were the first to indicate that one of the EcR complex
proteins, ultraspiracle, is also a receptor for JH
(Jones and Sharp, 1997; Jones et al., 2001; Xu et al.,
2002). More recently, Konopova and Jindra (2007)
used RNAi-aided knock-down of the Drosophila
Methoprene tolerant gene (Met) ortholog in the
flour beetle, Tribolium castaneum, to demonstrate
precocious metamorphosis of early-stage beetle larvae
and that the TcMet RNAi insects’ phenotypes
were similar to those observed for allatectomized
lepidopteran larvae. Results from more recent
work on the honeybee, Apis melifera, the mosquito,
Aedes aegypti, tobacco budworm, Heliothis virescens,
and T. castaneum show that the target proteins
involved in ecdysteroid (EcR and USP) and JH (Met)
action interact and mediate cross-talk between these
two important hormones (Bitra and Palli, 2009;
M507
L518
Q503
L420
V384
V416
(a) (b) (c)
A4: Addendum 183
Figure A1 The ligand-binding pockets of (a) BtEcR-LBD, showing PonA bound, (b) HvEcR-LBD, with PonA bound and (c) HvEcR-
LBD, showing the bisacylhydrazine BYI06830 bound. Pockets were generated both with a 1.4 A˚ radius probe (transparent green), as
well as with a 1.2 A˚ probe (black mesh to locate more loosely-packed regions of the pocket wall. The looser packing of the walls of
the HvEcR-LBD ligand-binding pocket in the vicinity of residues L420, V416 and Q503 is evidenced both by the orientation of the side
chains of these residues and by the intrusion into the protein atomic volume of the ecdysteroid-binding pocket wall calculated with
the 1.2 A˚ probe. Opening of this region upon BYI06830 binding is evident in (c), with the pocket volume now opening outwards to
solvent. No such region of looser packing is evident in the walls of the ligand-binding pocket of BtEcR-LBD (see panel a).
Reproduced with permission from Carmichael et al. (2005).
M507
L518
Li et al., 2007; Wu et al., 2006; Parthasarathy and
Palli, 2007, 2008a, 2008b; Franssens et al., 2006a;
2006b; Flatt et al., 2008). Li et al. (2007) identified
a JH response element (JHRE1) common to 16
genes regulated by JH III. These researchers showed
that two proteins (FKBP39 and Chd64) that were
identified using DNA affinity column prepared
using conserved JHRE1 interact with EcR, USP,
and Met proteins, suggesting that 20E and JHIII
may function through multiple protein complexes
that include proteins involved in signal transduction
of both these hormones. Some of the aforementioned
studies have been aided by the use of RNAi
approaches to knocking out the function of target
genes in both T. castaneum and Drosophila L57
cells (Parthasarathy et al., 2008; Li et al., 2007). In
spite of these studies, major gaps in our understanding
of the biochemical and molecular details of the
mode of action of JH and its analogs remain. At the
same time, it is studies like these that use diverse
systems, approaches, and tools, which will help us
gain a better understanding of the elusive mode of
action of JH and its analogs.
Studies like these, in combination with the ability
to use RNAi gene knock down approaches, not only
enhance our understanding of hormone action, but
also open up possibilities for intervening in new
protein targets that are critical to the growth and
development of insects.