The chicken type III GnRH receptor homologue is predominantly expressed in the pituitary, and exhibits similar ligand selectivity to the type I receptor

Abstract

Two 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 vs 19·8 nM) with more potent stimulation of inositol phosphate production (ED50: 0·8 vs 4·38 nM). Similar results were found for cGnRH-R-I, (Kd: 0·51 vs 10·8 nM) and (ED50: 0·7 vs 2·8 nM). The initial rate of internalisation was faster for cGnRH-R-III than cGnRH-R-I (26 vs 15·8%/min). Effects of GnRH antagonists were compared at the two receptors. Antagonist #27 distinguished between cGnRH-R-I and cGnRH-R-III (IC50: 2·3 vs 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.

Membrane rafts and GnRH receptor signaling

“…Interestingly, the mammalian type I receptor does differ from GnRH receptors found in non-mammalian vertebrates such as catfish [25] and Xenopus [26]. In contrast to the mammalian type I GnRHR, the non-mammalian GnRHRs do possess prototypical C-terminal tails, are phosphorylated by GRK’s and are characterized by more rapid internalization and desensitization kinetics [24, 27]. …”

Reproductive management of poultry

“…46,47 There is high expression of GnRHR3 in the pituitary gland. 48 Therefore, the releasing hormone for LH is chicken GnRH-I and the receptor is cGnRHR3.…”

Comparative and Evolutionary Aspects of Gonadotropin-Inhibitory Hormone and FMRFamide-Like Peptide Systems

“…By controlling gonadotropin secretion, GnIH regulates reproductive development and maintenance in birds (Ubuka et al, 2003 , 2006 ; Shimizu and Bédécarrats, 2006 ; Maddineni S. et al, 2008 ; Joseph et al, 2009 ) and mammals (Yano et al, 2004 ; Quennell et al, 2010 ; Sethi et al, 2010 ; Iwasa et al, 2012 ; Losa-Ward et al, 2012 ; Poling et al, 2012 ; Jørgensen et al, 2014 ; León et al, 2014 ; Soga et al, 2014 ; Zhao et al, 2014 ; Semaan and Kauffman, 2015 ; Xiang et al, 2015 ). GnIH regulates estrous or menstrual cycle in female mammals (Kriegsfeld et al, 2006 ; Gibson et al, 2008 ; Smith et al, 2010 ; Molnár et al, 2011 ; Clarke et al, 2012 ; Li et al, 2012 ; Salehi et al, 2013 ; Jørgensen et al, 2014 ; Russo et al, 2015 ).…”

“…As summarized earlier GnIH regulates reproductive activity in chordates by acting on GnRH neurons in the brain or gonadotropes in the pituitary or within the gonads (Hinuma et al, 2000 ; Tsutsui et al, 2000 ; Fukusumi et al, 2001 ; Ukena et al, 2002 , 2003b ; Bentley et al, 2003 , 2008 ; Ubuka et al, 2003 , 2005 , 2006 , 2008 , 2009b , c , 2012a , 2013 ; Yano et al, 2003 , 2004 ; Yoshida et al, 2003 ; Ciccone et al, 2004 ; Osugi et al, 2004 , 2012 ; Amano et al, 2006 ; Kriegsfeld et al, 2006 ; Shimizu and Bédécarrats, 2006 , 2010 ; Johnson et al, 2007 ; Clarke et al, 2008 , 2012 ; Dardente et al, 2008 ; Gibson et al, 2008 ; Johnson and Fraley, 2008 ; Maddineni S. et al, 2008 ; Maddineni S. R. et al, 2008 ; Murakami et al, 2008 ; Revel et al, 2008 ; Small et al, 2008 ; Smith et al, 2008 , 2010 , 2012 ; Anderson et al, 2009 ; Ducret et al, 2009 ; Gingerich et al, 2009 ; Joseph et al, 2009 ; Kadokawa et al, 2009 ; Legagneux et al, 2009 ; Qi et al, 2009 , 2013 ; Rizwan et al, 2009 , 2012 ; Sari et al, 2009 ; Wu et al, 2009 ; Chowdhury et al, 2010 ; Mason et al, 2010 ; McGuire and Bentley, 2010 ; Pineda et al, 2010a , b ; Quennell et al, 2010 ; Sethi et al, 2010 ; Tobari et al, 2010 ; Zhang et al,…”