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Inside JEB |
INKA CELLS GET INSECTS OUT OF A TIGHT SPOT
kathryn{at}biologists.com
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When a growing insect shrugs off its restrictive outer layer, ready to
replace it with a looser fitting cuticle, the process is tightly choreographed
by hormone peptides that trigger a set of pre-programmed manoeuvres to rid the
insect of the unwanted layer. Dusan 
it
an and colleagues had
already studied ecdysis in fruit flies and two moth species, and discovered
that two of the key hormones involved in the three insects' life changes are
released by a group of cells in their tracheas, called Inka cells. But would
other insects use the same mechanism for triggering their own instar-to-instar
transition?
Working with an international team of researchers, itan
began testing 26 species, ranging from primitive silverfish and dragonflies up
to relatively advanced insects such as ants, for evidence of peptides that
might trigger ecdysis (p.
1275). They tested Inka cells from each insect's tracheae, and found
that the cells produced hormone peptides that were structurally similar to the
moth and fruit fly ecdysis hormones. The team also injected silk moth larvae
with tracheal extracts from several different insects to see whether the
peptides could produce ecdysis; the silk moths began shedding their skins,
proving that the extracts contained ecdysis-triggering hormones. But when the
team looked at the number, size and distributions of Inka cells across the
species, each insect had its own unique cell pattern and distribution, even
though the hormones they produce are closely related.
References
itan, D., itanová, I.,
Spalovská, I., Takác, P., Park, Y. and Adams, M. E.
(2003). Conservation of ecdysis-triggering hormone signalling in
insects. J. Exp. Biol.
206,1275
-1289.
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