LPXRFa peptide system in the European sea bass: A molecular and immunohistochemical approach

Abstract

Gonadotropin-inhibitory hormone (GnIH) is a neuropeptide that suppresses reproduction in birds and mammals by inhibiting GnRH and gonadotropin secretion. GnIH orthologs with a C-terminal LPXRFamide (LPXRFa) motif have been identified in teleost fish. Although recent work also suggests its role in fish reproduction, studies are scarce and controversial, and have mainly focused on cyprinids. In this work we cloned a full-length cDNA encoding an LPXRFa precursor in the European sea bass, Dicentrarchus labrax. In contrast to other teleosts, the sea bass LPXRFa precursor contains only two putative RFamide peptides, termed sbLPXRFa1 and sbLPXRFa2. sblpxrfa transcripts were expressed predominantly in the olfactory bulbs/telencephalon, diencephalon, midbrain tegmentum, retina, and gonads. We also developed a specific antiserum against sbLPXRFa2, which revealed sbLPXRFa-immunoreactive (ir) perikarya in the olfactory bulbs-terminal nerve, ventral telencephalon, caudal preoptic area, dorsal mesencephalic tegmentum, and rostral rhombencephalon. These sbLPXRFa-ir cells profusely innervated the preoptic area, hypothalamus, optic tectum, semicircular torus, and caudal midbrain tegmentum, but conspicuous projections also reached the olfactory bulbs, ventral/dorsal telencephalon, habenula, ventral thalamus, pretectum, rostral midbrain tegmentum, posterior tuberculum, reticular formation, and viscerosensory lobe. The retina, pineal, vascular sac, and pituitary were also targets of sbLPXRFa-ir cells. In the pituitary, this innervation was observed close to follicle-stimulating hormone (FSH), luteinizing hormone (LH) and growth hormone (GH) cells. Tract-tracing retrograde labeling suggests that telencephalic and preoptic sbLPXRFa cells might represent the source of pituitary innervation. The immunohistochemical distribution of sbLPXRFa cells and fibers suggest that LPXRFa peptides might be involved in some functions as well as reproduction, such as feeding, growth, and behavior.

Molecular, cellular, morphological, physiological and behavioral aspects of gonadotropin-inhibitory hormone

“…In sockeye salmon, goldfish GnIH (LPXRFamide peptide)-ir cell bodies are located in the nucleus posterioris periventricularis of the hypothalamus and immunoreactive fibers are distributed in the pituitary and various brain regions (Amano et al, 2006) (Table 1). Paullada-Salmerón et al (2015) developed a specific antiserum against sea bass GnIH (sbLPXRFa), which revealed sbLPXRFa-ir perikarya in the olfactory bulbs-terminal nerve, ventral telencephalon, caudal POA, dorsal mesencephalic tegmentum and rostral rhombencephalon, and sbLPXRFa-ir fibers innervate the POA, hypothalamus, optic tectum, semicircular torus and caudal midbrain tegmentum, olfactory bulbs, ventral/dorsal telencephalon, habenula, ventral thalamus, pretectum, rostral midbrain tegmentum, posterior tuberculum, reticular formation and viscerosensory lobe, retina, pineal, vascular sac, and pituitary (Table 1). In the pituitary, sbLPXRFa-ir innervation was observed close to follicle-stimulating hormone (FSH), luteinizing hormone (LH), and GH cells (Table 1).…”

“…The grass puffer gene encodes a precursor polypeptide that may produce peptides that have C-terminal MPMRFamide or MPQRFamide sequence and one -RYamide peptide but not LPXRFamide (X = L or Q) peptides (Shahjahan et al, 2011). A polypeptide of European sea bass, which is orthologous to LPXRFamide precursor polypeptide also contains C-terminal MPMRFamide and MPQRFamide peptide sequences but not LPXRFamide (X = L or Q) peptides (Paullada-Salmerón et al, 2015).…”

Testicular Steroidogenesis and Locomotor Activity Are Regulated by Gonadotropin-Inhibitory Hormone in Male European Sea Bass

“…On the other hand, several studies have also reported that GNIH and/or its receptor (GNIHR) are expressed in gonads [21–24, 28] and are involved in the regulation of steroidogenesis in avian and mammalian species [23, 24, 26, 29]. In fish, the mechanisms of actions of Gnih on gonadotropin release and the reproductive axis are not so clear and contradictory findings have been reported [16, 18, 19, 45, 61, 62]. In addition, Gnih functions and implications in steroidogenesis and gametogenesis in teleosts have not been sufficiently assessed.…”

“…This species has also represented an interesting fish model for the study of environmental and endocrine control of reproduction [18, 34–45]. Recently, we identified a gnih gene in sea bass encoding a prepro- gnih mRNA that gives rise to two different RFamide peptides, named as sbGnih-1 and sbGnih-2, which are produced by proteolytic processing from a single protein precursor [45]. In a previous study [18], we reported an inhibitory role of Gnih (mainly sbGnih-2) in the reproductive axis of sea bass by acting at the brain and pituitary level.…”

Inhibitory Control of the Brain-Pituitary Reproductive Axis of Male European Sea Bass: Role of Gonadotropin Inhibitory Hormone

“…Moreover, GnIH and its homologous peptide inhibit the release of gonadotropin in higher vertebrates. In a search for novel factors regulating reproduction of fish using the D. labrax as a model [22], Paullada-Salmerón and colleagues isolated a GnIH ortholog precursor containing two putative GnIH peptides (sbGnIH-1 and sbGnIH-2). However, studies in fish have shown both stimulatory and inhibitory roles of GnIH in the reproductive axis by using pituitary cultures and intraperitoneal injection.…”