Identification and distribution of CCK-related peptides and mRNAs in the rainbow trout, Oncorhynchus mykiss

Peptides homologous to mammalian cholecystokinin (CCK), and their correspon ding cDNAs, have been isolated and sequenced from the rainbow trout. Oncorh ynchus mykiss. Three cDNAs encoding CCK-like preprohormones were identified from the brain. The cDNAs encode three different putative CCK-8 peptides c ontaining Asn, Leu or Thr, in position 6 (counting from the C-terminus). He nce, the trout CCKs are named CCK-N, CCK-L and CCK-T respectively. RT-PCR s howed differential expression of the three mRNAs although all were detected in the brain and intestine, similar to the expression pattern of CCK in te trapods. In situ hybridization on trout brain sections using S-35-labeled g ene-specific antisense oligonucleotides showed that the three mRNAs were pr esent in different parts, suggesting that the three CCK peptides may have d ifferent functions in the brain. Purification of CCR-immunoreactive materia l from the trout brain resulted in two CCK octapeptides: DYNGWMDF . NH2 (CC K-N) and DYLGWMDF . NH2 (CCK-L) present in equal amounts. In the pyloric ca eca, three forms of CCK-L were identified, consisting of 7, 8 and 21 residu es, respectively. The last was dominating and had the sequence ASGPGPSHKIKD RDYLGWMDF . NH2. All isolated peptides were fully sulfated. The trout is th e first species in which three different CCK-like cDNAs have been identifie d. (C) 2001 Elsevier Science B.V. All rights reserved.