Two gonadotropin-releasing hormone receptors in the African catfish: no differences in ligand selectivity, but differences in tissue distribution.
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).
Bogerd
Jan
J
Research Group Endocrinology, Utrecht University, 3584 CH Utrecht, The Netherlands. j.bogerd@bio.uu.nl
Diepenbroek
W Bas
WB
Hund
Eveline
E
van Oosterhout
Floor
F
Teves
Ana C C
AC
Leurs
Rob
R
Blomenröhr
Marion
M
D000595:Amino Acid Sequence; D000818:Animals; D002397:Catfishes; D002462:Cell Membrane / Q000378:metabolism; D003001:Cloning, Molecular; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes; D008024:Ligands; D008969:Molecular Sequence Data; D009928:Organ Specificity; D010053:Ovary; D010802:Phylogeny; D012333:RNA, Messenger / Q000032:analysis; D011966:Receptors, LHRH / Q000032:analysis* / Q000235:genetics / Q000378:metabolism*
D007457:Iodine Radioisotopes; D008024:Ligands; D012333:RNA, Messenger; D011966:Receptors, LHRH