The GnRH system in the European sea bass (Dicentrarchus labrax)

Abstract

The cDNA sequences encoding three GnRH forms, sea bream GnRH (sbGnRH), salmon GnRH (sGnRH) and chicken GnRH II (cGnRH II), were cloned from the brain of European sea bass, Dicentrarchus labrax. Comparison of their deduced amino acid sequences to the same forms in the gilthead sea bream, Sparus aurata, and striped bass, Morone saxatilis, revealed high homology of the prepro-cGnRH II (94% and 98% respectively), and prepro-sGnRH (92% to both species). The sbGnRH exhibited dissimilar identities, with high homology to the striped bass (93%), and lower homology (59%) to the gilthead sea bream. Two transcript types were identified for the GnRH-associated peptide (GAP)-sGnRH as well as for the GAP-cGnRH II, which suggests a possible alternative splicing followed by the addition of an early stop codon. In order to obtain antibodies specific for the three GnRH precursors, recombinant GAP proteins were produced. The differential expression of the three GnRHs previously reported in the brain by means of in situ hybridization, using riboprobes corresponding to the GAP-coding regions, was fully confirmed by immunocytochemistry using antibodies raised against the recombinant GAP proteins, indicating that the transcripts are translated into functional proteins. Moreover, this approach allowed us to follow, for the first time, the specific projections of the different cell groups: sGAP fibers are distributed mainly in the forebrain with few projections reaching the pituitary, sbGAP fibers are mainly present in the preoptic area, mediobasal hypothalamus and predominantly project to the pars distalis of the pituitary, whereas cGnRH II fibers have a widespread distribution primarily in the posterior brain, and do not project to the pituitary. These new tools will be extremely useful to study further the development, regulation and functional significance of three independent GnRH systems in the brain of vertebrate species.

mRNA expression of GnRH variants and receptors in the brain, pituitary and ovaries of pejerrey (Odontesthes bonariensis) in relation to the reproductive status

“…Taking into account that this peptide was undetectable in the pituitary of different teleosts (Senthilkumaran et al 1999;Amano et al 2002;González-Martínez et al 2002;Zmora et al 2002), and cGnRH-II levels in fish brain remain constant during the sexual cycle in some species (Collins et al 2001;Dufour et al 1993;Okuzawa et al 1990;Senthilkumaran et al 1999), cGnRH-II does not seem to be directly involved in gonadotropin secretion. However, there are also reports suggesting that cGnRH-II may be involved in the regulation of pituitary function in other teleost species: (1) (3) it has also a well-documented gonadotropin-releasing activity (Mylonas and Zohar 2001).…”

GnRH systems of Cichlasoma dimerus (Perciformes, Cichlidae) revisited: a localization study with antibodies and riboprobes to GnRH-associated peptides

“…Furthermore, the appearance of the three GnRH systems at different developmental stages reinforces the specificity of the tools used in this study. Zamora et al (2002) have demonstrated that the sea bass cDNAs encoding for the precursors of sGnRH and cGnRH II have 87%-99% sequence identity with the corresponding sequences from other perciforms, viz., striped bass, sea bream, and African cichlid. In turn, the sbGnRH precursor sequence identity is approximately 90% similar to that of the striped bass and 40%-60% similar to that of the sea bream and African cichlid.…”

Afferent and Efferent Connections of the Pineal Organ in the European Sea Bass <i>Dicentrarchus labrax:</i> A Carbocyanine Dye Tract-Tracing Study

“…Catecholaminergic cells were also observed within the ventromedial thalamic nucleus, around the fasciculus retroflexus (periventricular pretectum), the posterior commissure and the dorsolateral thalamic nucleus, as well as in the posterior tubercle of this species [Batten et al, 1993]. Recently, the presence of kisspeptin 1 and GnRH-II cells was described in the habenula and medial tegmental area of the sea bass, respectively [González-Martínez et al, 2001Zmora et al, 2002;Escobar et al, 2010]; both neuropeptidergic systems are implicated in the processing of environmental and metabolic information . The habenula, dorsal and ventral thalamus, posterior tubercle and mesencephalic tegmentum also contain NPYimmunoreactive neurons in other teleost and non-teleost species [Pontet et al, 1989;Batten et al, 1990;Vecino and Ekström, 1992;García-Fernández et al, 1992;Subhedar et al 1996;Castro et al, 1999;Rodríguez-Gómez et al, 2001;Chiba, 2005].…”