Regulation of gonadotropin-releasing hormone (GnRH)-receptor gene expression in tilapia: effect of GnRH and dopamine.
The present work was designed to study certain aspects of the endocrine regulation of gonadotropin-releasing hormone receptor (GnRH-R) in the pituitary of the teleost fish tilapia. A GnRH-R was cloned from the pituitary of hybrid tilapia (taGnRH-R) and was identified as a typical seven-transmembrane receptor. Northern blot analysis revealed a single GnRH-R transcript in the pituitary of approximately 2.3 kilobases. The taGnRH-R mRNA levels were significantly higher in females than in males. Injection of the salmon GnRH analog (sGnRHa; 5-50 microg/kg) increased the steady-state levels of taGnRH-R mRNA, with the highest response recorded at 25 microg/kg and at 36 h. At the higher dose of sGnRHa (50 microg/kg), taGnRH-R transcript appeared to be down-regulated. Exposure of tilapia pituitary cells in culture to graded doses (0.1-100 nM) of seabream (sbGnRH = GnRH I), chicken II (cGnRH II), or salmon GnRH (sGnRH = GnRH III) resulted in a significant increase in taGnRH-R mRNA levels. The highest levels of both LH release and taGnRH-R mRNA levels were recorded after exposure to cGnRH II and the lowest after exposure to sbGnRH. The dopamine-agonist quinpirole suppressed LH release and mRNA levels of taGnRH-R, indicating an inhibitory effect on GnRH-R synthesis. Collectively, these data provide evidence that GnRH in tilapia can up- regulate, whereas dopamine down-regulates, taGnRH-R mRNA levels.
Levavi-Sivan
Berta
B
Department of Animal Sciences, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University, Rehovot 76100, Israel. sivan@agri.huji.ac.il
Safarian
Helena
H
Rosenfeld
Hanna
H
Elizur
Abigail
A
Avitan
Ayelet
A
D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D004298:Dopamine / Q000494:pharmacology; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects; D007987:Gonadotropin-Releasing Hormone / Q000235:genetics / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000378:metabolism; D008297:Male; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism; D019257:Quinpirole / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011966:Receptors, LHRH / Q000235:genetics*; D012727:Sex Characteristics; D017210:Tilapia / Q000235:genetics* / Q000378:metabolism
D012333:RNA, Messenger; D011966:Receptors, LHRH; D019257:Quinpirole; D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone; D004298:Dopamine