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First published online January 31, 2007
Journal of Experimental Biology 210, 699-714 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02696
Midgut epithelial endocrine cells are a rich source of the neuropeptides APSGFLGMRamide (Cancer borealis tachykinin-related peptide Ia) and GYRKPPFNGSIFamide (Gly1-SIFamide) in the crabs Cancer borealis, Cancer magister and Cancer productus
1 Department of Biology, University of Washington, Box 351800, Seattle, WA
98195-1800, USA
2 Mount Desert Island Biological Laboratory, PO Box 35, Old Bar Harbor Road,
Salisbury Cove, ME 04672, USA
3 Department of Chemistry, University of Wisconsin-Madison, 1101 University
Avenue, Madison, WI 53706-1369, USA
4 Department of Chemistry, Bowdoin College, 6600 College Station, Brunswick,
ME 04011, USA
5 School of Pharmacy, University of Wisconsin-Madison, 777 Highland Avenue,
Madison, WI 53705-2222, USA
6 Department of Biology, Bowdoin College, 6500 College Station, Brunswick,
ME 04011, USA
* Author for correspondence (e-mail: crabman{at}u.washington.edu)
Accepted 13 December 2006
Over a quarter of a century ago, Mykles described the presence of putative endocrine cells in the midgut epithelium of the crab Cancer magister (Mykles, 1979). In the years that have followed, these cells have been largely ignored and nothing is known about their hormone content or the functions they play in this species. Here, we used a combination of immunohistochemistry and mass spectrometric techniques to investigate these questions. Using immunohistochemistry, we identified both SIFamide- and tachykinin-related peptide (TRP)-like immunopositive cells in the midgut epithelium of C. magister, as well as in that of Cancer borealis and Cancer productus. In each species, the SIFamide-like labeling was restricted to the anterior portion of the midgut, including the paired anterior midgut caeca, whereas the TRP-like immunoreactivity predominated in the posterior midgut and the posterior midgut caecum. Regardless of location, label or species, the morphology of the immunopositive cells matched that of the putative endocrine cells characterized ultrastructurally by Mykles (Mykles, 1979). Matrix-assisted laser desorption/ionization-Fourier transform mass spectrometry identified the peptides responsible for the immunoreactivities as GYRKPPFNGSIFamide (Gly1-SIFamide) and APSGFLGMRamide [Cancer borealis tachykinin-related peptide Ia (CabTRP Ia)], respectively, both of which are known neuropeptides of Cancer species. Although the function of these midgut-derived peptides remains unknown, we found that both Gly1-SIFamide and CabTRP Ia were released when the midgut was exposed to high-potassium saline. In addition, CabTRP Ia was detectable in the hemolymph of crabs that had been held without food for several days, but not in that of fed animals, paralleling results that were attributed to TRP release from midgut endocrine cells in insects. Thus, one function that midgut-derived CabTRP Ia may play in Cancer species is paracrine/hormonal control of feeding-related behavior, as has been postulated for TRPs released from homologous cells in insects.
Key words: brain-gut peptide, immunohistochemistry, laser-scanning confocal microscopy, matrix-assisted laser desorption/ionizaton-Fourier transform mass spectrometry, MALDI-FTMS
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