The complementary DNAs (cDNA) encoding the [Trp 7 ,Leu 8 ]-gonadotrophin-releasing hormone (salmon-type GnRH; sGnRH:GeneBank accession no. u60667) and the [His 5 ,Trp 7 ,Tyr 8 ]-GnRH (chicken-II-type GnRH; cGnRH-II: GeneBank accession no. u60668) precursor in the roach (Rutilus rutilus) were isolated and sequenced following reverse transcription and rapid amplification of cDNA ends (RACE). The sGnRH and cGnRH-II precursor cDNAs consisted of 439 and 628 bp, and included open reading frames of 282 and 255 bp respectively. The structures of the encoded peptides were the same as GnRHs previously identified in other vertebrates. The sGnRH and cGnRH-II precursor cDNAs, including the non-coding regions, had 88·6 and 79·9% identity respectively, to those identified in goldfish (Carassius auratus). However, significant similarity was not observed between the non-coding regions of the GnRH cDNAs of Cyprinidae and other fish. The presumed third exon, encoding partial sGnRH associated peptide (GAP) of roach, demonstrated significant nucleotide and amino acid similarity with the appropriate regions in the goldfish, but not with other species, and this may indicate functional differences of GAP between different families of fish. cGnRH-II precursor cDNAs from roach had relatively high nucleotide similarity across this GnRH variant. Cladistic analysis classified the sGnRH and cGnRH-II precursor cDNAs into three and two groups respectively. However, the divergence between nucleotide sequences within the sGnRH variant was greater than those encoding the cGnRH-II precursors. Consistent with the consensus developed from previous studies, Northern blot analysis demonstrated that expression of sGnRH and cGnRH-II was restricted to the olfactory bulbs and midbrain of roach respectively. This work forms the basis for further study on the mechanisms by which the tapeworm, Ligula intestinalis, interacts with the pituitary-gonadal axis of its fish host.

The cDNA encoding the [His5Trp7Tyr8] gonadotropin‐releasing hormone (chicken‐II‐type GnRH; cGnRH‐II) precursor from rainbow trout Oncorhynchus mykiss has been sequenced using reverse transcription and rapid amplification of cDNA ends (RACE). The precursor cDNA is 544 bp from which an open reading frame of 258 bases encodes a 86 amino acid precursor. The tripartite structure of the encoded peptide is identical to all other GnRHs reported to date. The rainbow trout cGnRH‐II cDNA, including both the precursor encoding and non‐coding regions, shared 52–80% identity with others of this variant characterized in fish. When the individual components that encode the tripartite structure were compared, identity was significant across the GnRH, signal and associated peptide encoding regions. Nucleotide similarity between non‐coding regions were generally low. In trout, only the cGnRH‐II, but not the signal or associated peptide encoding region, shared significant similarity to the cGnRH‐II precursor cDNAs characterized from the tree shrew. Cladistic analysis using the bases encoding cGnRH‐II precursors resulted in their broad division into two, fish and tree shrew. The fish could be classified generally into two, the Ostariophysi (siluriforms and cypriniforms) and Acanthopterygii (perciforms) together with the Protacanthoptergyii (salmoniforms). Trout shared greatest homology with the Acanthopterygii. Northern analyses identified a single transcript that was expressed in the midbrain only.