Two Gonadotropin-Releasing Hormone Receptors in the African Catfish: No Differences in Ligand Selectivity, but Differences in Tissue Distribution

• Published in: Endocrinology (Philadelphia) Vol. 143; no. 12; pp. 4673 - 4682
• Main Authors: Bogerd, Jan, Diepenbroek, W. Bas, Hund, Eveline, van Oosterhout, Floor, Teves, Ana C. C, Leurs, Rob, Blomenröhr, Marion
• Format: Journal Article
• Language: English
• Published: United States Endocrine Society 01.12.2002
• Subjects: Amino Acid Sequence; Animals; Catfishes; Cell Membrane - metabolism; Cloning, Molecular; Female; Humans; Iodine Radioisotopes; Ligands; Molecular Sequence Data; Organ Specificity; Ovary; Phylogeny; Receptors, LHRH - analysis; Receptors, LHRH - genetics; Receptors, LHRH - metabolism; RNA, Messenger - analysis
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/en.2002-220578

Ligand-binding studies revealed the presence of GnRH-binding sites in African catfish ovary. However, our expression profiling studies failed to detect the previously identified catfish GnRH receptor (cfGnRH-R1) mRNA in this tissue. This negative result instigated us to clone an additional catfish GnRH receptor (cfGnRH-R2) cDNA and study its expression in different tissues in conjunction with the expression of the two catfish GnRH (i.e. cfGnRH and cGnRH-II) genes. The highest cfGnRH-R1 and cfGnRH-R2 mRNA levels were detected in pituitary for cfGnRH-R1 and in brain and ovary for cfGnRH-R2. cfGnRH mRNA was coexpressed with cfGnRH-R1 mRNA in pituitary and brain and with cfGnRH-R2 mRNA in brain and ovary. Ubiquitous expression of cGnRH-II mRNA was observed in all tissues tested, with the highest expression in brain, heart, pituitary, ovary, and head-kidney. Binding studies revealed that cfGnRH-R1 had a higher affinity than cfGnRH-R2 for cGnRH-II, cfGnRH, and various other GnRH agonists. However, this was not reflected in the inositol phosphate or cAMP signal transduction properties of both types of cfGnRH-R. We therefore conclude that in catfish, functional ligand/receptor units evolved by restricted coexpression of a particular receptor in combination with a particular GnRH in particular (nearby) tissue(s).