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Endocrine cascades during ecdysis in decapod crustaceans
 For insects, much is known concerning the precisely coordinated series of endocrine cascades culminating in successful ecdysis. Progress in this area has been rapid in view of the availability of genomic information for Drosophila, and of course, the extensive mutant background of this model. For crustaceans, much less is known. Nevertheless, we are beginning to dissect the neurohormonal pathways associated with ecdysis in crabs. Notwithstanding the very different ways in which both groups of arthropods control synthesis of ecdysteroids (moulting hormones)- in insects ecdysteroidogenesis is stimulated by prothoracicotropic hormone (PTTH), yet in crustaceans, this process is inhibited by moult-inhibiting hormone (MIH), there seem to be some endocrine cascades which occur during ecdysis (crustacean cardioactive peptide, and some newly discovered neurohormones!), which are common to both groups of arthropods. However, there are some that are unique to crustaceans, for example the release of crustacean hyperglycaemic hormone from gut endocrine cells prior to ecdysis, which result in water uptake, thus leading to post-ecdysial swelling. Whilst decapod crustaceans are of course genetically intractable, they offer some advantages, not least in terms of their size, which allows real-time monitoring of hormone titres. Furthermore the impending completion of the first crustacean genome (Daphnia) (http://wfleabase.org/), will allow comparison from a post-genomic perspective, thus opening up an extremely exciting new era in crustacean endocrinology, which will completely transform the field!
Funded by BBSRC.
Researchers: Dr S.G. Webster, Dr J S Chung |
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The red crabs of Christmas Island, roles of crustacean hyperglycaemic hormone in diel and seasonal migration physiology
 The annual migration of red crabs, which are endemic to Christmas Island in the Indian Ocean has rightly been called one of the great spectacles of the natural world. Each year, at the start of the wet season, on full moon, many millions of mature male and female red crabs (Gecarcoidea natalis) migrate to the shores of the island to interact, mate and spawn. This migration involves significant energy demands on the crabs, but during the dry season, crabs are relatively inactive. Furthermore, since these crabs are entirely terrestrial, there are opposing burdens placed upon their osmoregulatory mechanisms during the year. Evidence is now accumulating suggesting that a key adaptive hormone, which influences energy mobilisation and osmoregulatory capacity in red crabs is the well known crustacean hyperglycaemic hormone (CHH). Since this crab shows extreme adaptation to seasonal xeric/wet conditions and undergoes long, energy demanding migrations, we are now in the enviable position of being able to further define the roles of this hormone in these processes, by careful measurement of CHH titres and corresponding gene expression profiles from samples collected in the field during diel and seasonal cycles. In a parallel project, we seek to understand the analogous processes in the blue crab, Discoplax hirtipes.
Please note: This project is funded to, and coordinated by, the principal investigator, Professor Steve Morris, Bristol University, to whom enquiries should be made.
Funded by NERC.
Researchers: Prof. S. Morris, Dr U. Postel, Ms Lucy Turner (Bristol), Dr. S.G. Webster (Bangor) |
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Molecular neurogenetics of rhythmicity in intertidal crustaceans
 The major environmental variable affecting interdidal organisms is the daily ebb and flow of the tides. Accordingly, in all examples so far studied, anticipation of immersion, via a so called endogenous, free-running, “circatidal clock” with a period of ca. 12.4h seems to be universal. In contrast, it has been long known that terrestrial organisms possess biological clocks which free-run with an approximate 24h rhythm. The molecular components which make up the circadian clock have been widely conserved in friutflies (Drosophila), rodents and other mammals, and the interacting feedback and feedforward loops involved in maintenance of the circadian oscillators (the clock) are well known. In contrast, we know nothing about the molecular mechanisms involved in the circatidal clock- Is it just a circadian clock(s) running at twice the speed? Or are there new components; indeed is there a novel circatidal clock, which must, in evolutionary terms pre-date that of the terrestrial circadian counterpart?
We are examining this problem by using a model crustacean which possesses extraordinarily robust circatidal rhythms, the speckled sea louse, Eurydice pulchra. This animal is useful since its circatidal rhythms can be salvaged in arrhythmic animals, by cycles of turbulence (shaking) at 12h intervals. Accordingly, we have developed a head tissue microarray, which we are interrogating with mRNA (fluor- labelled cDNA) from timed series of animals exposed to ciracatidal and circadian entrainment regimes, to eventually identify genes whose transcript abundance varies over 12.4 or 24h periodicities. Further to this, we are examining neurones in the brain, which express canonical circadian transcripts/ proteins (Per, Clock, Cycle), to see whether changes in cyclical abundance of these “circadian” genes change according to circatidal or circadian regimes.
This project is coordinated by Professor C.P. Kyriacou (Leicester), and involves the invaluable input of Dr. M.H. Hastings, who first described the rhythmic behaviour of Eurydice in detail over 20 years ago!
Funded by BBSRC
Researchers: Prof. C.P. Kyriacou, Dr L. Zhang (Leicester), Dr. D.C. Wilcockson, Dr, S.G. Webster (Bangor), Dr. M.H. Hastings (LMB Cambridge). |
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