Evidence of rainbow trout prolactin interaction with its receptor through unstable homodimerisation

This study aims to characterise Prolactin receptor (PRLR) in rainbow trout for which no information is available despite the availability of Salmonid PRL preparations. By screening a freshwater rainbow trout intestine cDNA li brary with a probe corresponding to the extracellular domain (ECD) of tilap ia PRLR, we have cloned a 2.5 kb insert coding for the PRLR. The mature pro tein of 614 amino acid residues is similar to PRLR isolated in tilapia and also the long form of mammalian PRLR. Analysis of PRLR gene expression in o smoregulatory organs revealed the presence of a unique transcript, thus con firming the involvement of this hormone in the control of osmoregulation in this fish species. By using surface plasmon resonance (SPR) technology, ki netic measurement of interaction between trout PRL and its receptor ECD was studied. This approach allowed us to demonstrate the formation of a transi ent, unstable homodimeric complex. This unstability could explain the inabi lity to perform binding experiments using homologous PRL. In contrast, hete rologous lactogenic ligands were able to interact through a more stable com plex. Whether these characteristics of PRL-receptor interaction in rainbow trout are different to what occurs in tilapia where a homologous radiorecep tor assay was developed would require further studies. (C) 2001 Elsevier Sc ience Ireland Ltd. All rights reserved.