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This Article Accepted manuscript (PDF) All Versions of this Article: JOE-08-0544v1 202/1/179    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Joseph, N. Articles by Dunn, I. Search for Related Content PubMed PubMed Citation Articles by Joseph, N. Articles by Dunn, I.

N Joseph, Genetics and Genomics, The Roslin Institute, Edinburgh, United Kingdom
K Morgan, The Queens Medical Research Institute, MRC human reproductive sciences unit, edinburgh, United Kingdom
R Sellar, The Queens Medical Research Institute, MRC Human Reproductive Sciences Unit, Edinburgh, United States
D McBride, Genetics and Genomics, The Roslin Institute, Edinburgh, United Kingdom
R Millar, The Queens Medical Research Institute, MRC Human Reproductive Sciences Unit, Edinburgh, United Kingdom
I Dunn, Genetics and Genomics, The Roslin Institute, Edinburgh, United Kingdom

Correspondence: Nerine Joseph, Email: nerine.joseph{at}bbsrc.ac.uk

Two gonadotrophin releasing hormone (GnRH) isoforms (cGnRH-I and GnRH-II) and two GnRH receptor subtypes (cGnRH-R-I and cGnRH-R-III) occur in chickens. Differential roles for these molecules in regulating gonadotrophin secretion or other functions are unclear. To investigate this we cloned cGnRH-R-III from a broiler chicken and compared its structure, expression and pharmacological properties with cGnRH-R-I. The broiler cGnRH-R-III cDNA was 100% identical to the sequence reported in the red jungle fowl and white leghorn breed. Pituitary cGnRH-R-III mRNA was ~1400 fold more abundant than cGnRH-R-I mRNA. Northern analysis indicated a single cGnRH-R-III transcript. A pronounced sex and age difference existed, with higher pituitary transcript levels in sexually mature females versus juvenile females. In contrast, higher expression levels occurred in juvenile males versus sexually mature males. Functional studies in COS-7 cells indicated that cGnRH-R-III has a higher binding affinity for GnRH-II than cGnRH-I (Kd: 0.57 v 19.8 nM) with more potent stimulation of inositol phosphate production (ED50: 0.8 v 4.38 nM). Similar results were found for cGnRH-R-I, (Kd: 0.51 v 10.8 nM) and (ED50: 0.7 v 2.8 nM). The initial rate of internalisation was faster for cGnRH-R-III than cGnRH-R-I (26%.min-1 v 15.8%.min-1). Effects of GnRH antagonists were compared at the two receptors. Antagonist #27 distinguished between cGnRH-R-I and cGnRH-R-III (IC50: 2.3 v 351 nM). These results suggest that cGnRH-R-III is probably the major mediator of pituitary gonadotroph function, that antagonist #27 may allow delineation of receptor subtype function in-vitro and in-vivo and that tissue-specific recruitment of cGnRH-R isoforms has occurred during evolution.