Lapatinib Interestingly GAL has also been shown to be co

Interestingly, GAL has also been shown to be co-expressed and/or secreted in luteinizing hormone releasing hormone (LHRH) (Merchenthaler et al., 1991, Marks et al., 1994) and kisspeptin (KISS) neurons (Porteous et al., 2011). Furthermore, GAL was shown to stimulate luteinizing hormone (LH) secretion in the pituitary (Sahu et al., 1994), suggesting a role in the activation of the LH surge and in the activation of gonadal steroid production at puberty onset. Conversely, 17β-estradiol (E2) treatments increased GAL binding in the uterus of immature castrated quails (Tsutsui et al., 1998) and changed the number and/or affinity of galanin-binding sites in several Lapatinib regions in rats (Planas et al., 1995), suggesting galanin receptors (GALR) may be regulated by gonadal steroids. The identification of three galanin receptor subtypes (GALR1, GALR2 and GALR3) in human and rats (Habert-Ortoli, 1994, Parker et al., 1995, Fathi et al., 1997, Wang et al., 1997a, Wang et al., 1997b, Kolakowski et al., 1998, Pang et al., 1998), allowed confirmation of a direct effect of sex steroids in the regulation of GALR1 and GALR2 gene transcription in the brain (Bouret et al., 2000). In addition, changes in GALR1 gene expression in the preoptic area during the estrous cycle were also detected (Faure-Virelizier et al., 1998), further confirming a regulation of GALRs by sex steroids, as found for the ligand. In fish, most studies have focused on the role of galanin on feeding regulation (reviewed by Mensah et al. (2010)) and few reports have dealt with its involvement in reproductive functions. As with mammalian species, fish display brain GAL-ir sexual dimorphism (Cornbrooks and Parsons, 1991a, Cornbrooks and Parsons, 1991b, Prasada Rao et al., 1996, Jadhao and Meyer, 2000) and in eels, GAL levels vary according to reproductive and physiological stages (Olivereau and Olivereau, 1991). In addition, in a preliminary in vitro study with goldfish pituitary cells galanin stimulated LH release (Prasada Rao et al., 1996), suggesting parallelism between fish and mammals in putative GAL reproductive functions. Information on galanin receptors in fish is even scarcer as to date there is only one in silico genome survey identifying putative ortholog GALR gene duplicates (GALR1a, GALR1b and GALR2) (Liu et al., 2010) and a report correlating the expression of zebrafish (Danio rerio) GALR1a in the intestine with different feeding regimes (Li et al., 2013). The European sea bass (Dicentrarchus labrax), henceforth designated sea bass, is an aquaculture species with a high incidence of precocious puberty in males, a problem that negatively affects productivity (Taranger et al., 2010). The present study aimed at identifying and characterizing sea bass ortholog GALRs and to investigate whether sex steroid treatments modify their expression in brain and testes of pre-pubertal fish.
Methods
Results
Discussion The present study identified two paralog pairs of GALR genes in sea bass, confirming a teleost specific duplication of GALR1 genes (dlGALR1a and dlGALR1b) and identifying novel GALR2 gene duplications in sea bass and tetrapod species, indicating a duplication prior to the teleost lineage. Additional characterization of these receptors suggested both dlGALR1 genes to be sensitive to 11KT in the testes of pre-pubertal fish. The genomic structure and deduced amino acid sequences of dlGALRs are highly conserved with the human GALR1 and GALR2 receptors. The sea bass GALR1 duplicate genes have a conserved genomic structure composed by three coding exons as previously described for human and mouse GALR1 genes (Jacoby et al., 1997, Iismaa et al., 1998). The first exon spans from the putative N-terminal onto the end of transmembrane region 5, the second exon includes the third intracellular loop and the third exon spans from transmembrane region 6 onto the putative C-terminus. The sea bass GALR2 gene duplicates also have a conserved two exon gene structure when compared to the mammalian ortholog GALR2 (Iismaa et al., 1998, Pang et al., 1998). The dlGALR2 duplicates first exon spans from the putative N-terminal onto the end of transmembrane region 3 and the second exon encodes from the second intracellular domain until the putative C-terminus.