Insect Biochemistry and Molecular Biology 30 2000 663–669 www.elsevier.comlocateibmb
The modes of action of juvenile hormones: some questions we ought to ask
K.G. Davey
Department of Biology, York University, Toronto, Ontario, Canada M3J 1P3 Received 31 October 1999; received in revised form 31 December 1999; accepted 25 January 2000
Abstract
This paper argues that the current dogma that juvenile hormones are structurally unique and constitute a family of derivatives of farnesoic acid which are produced by the corpus allatum CA, secreted into the hemolymph, frequently transported by binding
proteins, enter cells by diffusion across the cell membrane and there the products of the CA interact in some way with the genome, probably via nuclear receptors of the steroid superfamily, may not be tenable. It does so by examining the following questions.
How many JHs are there? Are there other sources of JH in insects? Are there non-farnesoids with JH activity in insects? How does JH get into cells? Is the product of the CA the effective hormone? How many modes of action are there? How many receptors
are there?
2000 Elsevier Science Ltd. All rights reserved.
Keywords: Juvenile hormone; Thyroid hormones; Receptors; Reproduction; Vitellogenesis; Metamorphosis
1. Introduction
Scientists toiling in any discipline are subject to a shared view of that field, which amounts to a commonly
held set of assumptions that direct the thinking in that field. We who work in insect endocrinology have
inherited a view from the pioneers of our subject about how juvenile hormone might effect its manifold actions.
This view has its origins in the notion that “insects pro- vide unrivalled material for physiological study”
Wigglesworth, 1976, and that insects, being simpler organisms, ought to be able to illuminate physiology in
general. We have perhaps translated that into a convic- tion that the endocrinology of insects is simpler, but we
are beginning to glimpse a complexity of action which rivals that of mammalian endocrine action. Moreover,
we are convinced, I suspect, that insects really are likely to be models for more complex organisms, and that the
wealth of information accumulated about the action of hormones in more complex organisms will be broadly
applicable to the JH field. It is not my objective to chal-
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0965-174800 - see front matter
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lenge this specific assumption, for that has already been done to a degree Jones, 1995.
I intend rather to examine a set of more specific assumptions about JH. Simply put, we appear jointly to
subscribe to the following dogma. Juvenile hormones are structurally unique among animals and constitute a fam-
ily of derivatives of farnesoic acid which are produced by the corpus allatum CA, secreted into the hemo-
lymph, transported by binding proteins, enter cells by diffusion across the cell membrane, and there the pro-
ducts of the CA interact in some way with the genome, probably via nuclear receptors of the steroid superfamily.
A scientist who is asked by colleagues to deliver a lec- ture at an international conference has a responsibility
to step back from the field a little and take a broader view. I intend to discharge that responsibility by raising
a number of questions about the assumptions that under- pin the dogma. In doing so, I will be highly selective
about the literature which I will quote: this is not intended to be another review on the action of JH. This
contribution is intended to provoke discussion and thought rather than answer questions: it is intended to
emphasise our ignorance rather than document our knowledge.
664 K.G. Davey Insect Biochemistry and Molecular Biology 30 2000 663–669
2. The questions
