Ž . Comparative Biochemistry and Physiology Part B 129 2001 575586 Cloning and expression of two isoforms of guanylate ž / ž cyclase C GC-C from the European eel Anguilla / anguilla Muriel M. Comrie, Christopher P. Cutler, Gordon Cramb  School of Biology, Bute Medical Buildings, Uni  ersity of St Andrews, St Andrews, Fife, KY16 9TS, UK Received 5 September 2000; received in revised form 10 November 2000; accepted 17 November 2000 Abstract Ž . Complementary DNA fragments for two isoforms of particulate guanylate cyclase C GC-C were cloned from the Ž . intestine of the European eel Anguilla anguilla . Both isoforms exhibited higher nucleotide and amino acid sequence Ž homologies to members of the GC-C family from other species than the related guanylate cyclase A or B GC-A or . GC-B isoforms from the eel. Northern blots indicated that probes for both isoforms, termed GC-C1 and GC-C2, selectively hybridised to 4.8-kb transcripts in the intestine and the kidney. Expression of the GC-C2 transcript in the intestine was increased by 100% following the transfer of yellow FW-acclimated eels to SW. Likewise developmental Ž . maturation of yellow eels into pre-migratory silver eels resulted in a significant increase 60% in the intestinal expression of GC-C2. No changes in expression of GC-C2 were seen in the kidney under any condition. RT-PCR indicated that the GC-C2 isoform is only expressed in anterior and mid-gut segments in FW-acclimated yellow eels. However, expression is also extended to the posterior gut segment when yellow eels are acclimated to SW or following developmental transformation into silver eels.  2001 Elsevier Science Inc. All rights reserved. Keywords: Anguilla; Eel; Intestine; Nucleotide sequence; Guanylate cyclase; GC-C; RT-PCR 1. Introduction Cyclic GMP is an important intracellular sec- ond messenger produced by an ever-expanding family of receptor guanylate cyclases. The guany- late cyclases exist either as cytosolic or mem- brane-associated forms; the cytosolic forms are  Corresponding author. Tel.: 44-1334-463530; fax: 44- 1334-463600. Ž . E-mail address: gc@st-and.ac.uk G. Cramb . heterodimers which are activated by nitric oxide or carbon monoxide and the membrane forms are single pass integral membrane proteins which are activated by various endogenous peptides. Pep- tide ligands that have been identified so far in- clude the members of natriuretic peptide family which comprise atrial, brain and C-type natri- Ž uretic peptides ANP, BNP and CNP, respec- . tively and the guanylin peptide family, compris- ing guanylin itself, uroguanylin and the most re- cently discovered lymphoguanylin. These peptides mediate their actions by binding and activating 1096-495901$ - see front matter  2001 Elsevier Science Inc. All rights reserved. Ž . PII: S 1 0 9 6 - 4 9 5 9 01 00367-0