Cloning, Characterization, and Tissue Distribution of Prolactin Receptor in the Sea Bream (Sparus aurata)

Abstract

The prolactin receptor (PRLR) was cloned and its tissue distribution characterized in adults of the protandrous hermaphrodite marine teleost, the sea bream (Sparus aurata). An homologous cDNA probe for sea bream PRLR (sbPRLR) was obtained by RT-PCR using gill mRNA. This probe was used to screen intestine and kidney cDNA libraries from which two overlapping clones (1100 and 2425 bp, respectively) were obtained. These clones had 100% sequence identity in the overlapping region (893 bp) and were used to deduce the complete amino acid sequence of sbPRLR. The receptor spans 2640 bp and encodes a protein of 537 amino acids. Features characteristic of PRLR, two pairs of cysteines, WS box, hydrophobic transmembrane domain, box 1, and box 2, were identified and showed a high degree of sequence identity to PRLRs from other vertebrate species. SbPRLR is 29 and 32% identical to tilapia (Oreochromis niloticus) and goldfish (Carassius auratus) PRLRs, respectively. In the sea bream two PRLR transcripts of 2.8 and 3.2 kb were detected in the intestine, kidney, and gills and a single transcript of 2.8 kb was detected in skin and pituitary by Northern blot. Spermiating gonads (more than 95% male tissue; gonado-somatic index of 0.6) contained, in addition to the 2.8-kb transcript, three more transcripts of 1.9, 1.3, and 1.1 kb. RT-PCR, which is a far more sensitive method than Northern blot, detected PRLR mRNA in gills, intestine, brain, pituitary, kidney, liver, gonads, spleen, head-kidney, heart, muscle, and bone. Immunohistochemistry using specific polyclonal antibodies raised against an oligopeptide from the extracellular domain of sbPRLR detected PRLR in several epithelial tissues of juvenile sea bream, including the anterior gut, renal tubule, choroid membrane of the third ventricle, saccus vasculosus, branchial chloride cells, and branchial cartilage.

Expression and cellular localization of insulin-like growth factor-II protein and mRNA in Sparus aurata during development

“…The function of the saccus has been suggested to be mainly concerned with homeostasis of the cerebrospinal fluid; others have suggested that it may be concerned with osmoregulation via the activity of ATPase enzymes involved in transport of Na + /K + and Mg 2+ /Ca 2+ (Jansen et al 1981). Observations of the presence of immunoreactive IGF-II (present study) and IGF-I (G Radaelli, M Patruno, L Maccatrozzo & B Funkenstein, unpublished observations) in the saccus of S. aurata, together with previous reports on immunoreactive prolactin receptors in this organ of S. aurata (Santos et al 2001) further support a role in osmoregulation. Other organs involved in osmoregulation also exhibited IGF-II immunoreactivity in the current study: skin, epithelial cells of the gill filaments and epithelium of kidney tubules.…”

Expression of prolactin-releasing peptide and prolactin in the euryhaline mudskippers (Periophthalmus modestus): prolactin-releasing peptide as a primary regulator of prolactin

“…Since such high extrapituitary expression has been reported only in teleosts such as rainbow trout, goldfish and other perciforms (Santos et al 1999, Yang et al 1999, Imaoka et al 2000, production of PRL might be centralized into pituitary during terrestrial tetrapod evolution. The larger size of extrapituitary PRL transcripts may reflect a difference of promoter usage as reported in mammalian lymphocytes and decidua, whose RNA transcripts are larger than the pituitary counterpart (Ben-Jonathan et al 1996).…”

“…However, the control of extrapituitary PRL expression is still poorly understood, both at the transcriptional and at the secretory levels (Goffin et al 2002). Since extrapituitary PRL expression in trout, goldfish and seabream has been reported to be relatively high, unlike that in tetrapods (Santos et al 1999, Yang et al 1999, Imaoka et al 2000, studies using aquatic teleosts should shed new light on the regulation of extrapituitary PRL in terrestrial vertebrates.…”

The role of prolactin in fish reproduction

“…PRLR sequences have been characterised for several species of fish, including goldfish [113], seabream [95], blue discus (Symphysodon aequifasciatus) [52], Japanese flounder (Paralichthys olivaceus) [41], starry flounder [72], fugu [59], and Nile tilapia [92]. These genes encode mature peptides of ca.…”

“…Firstly, PRLR mRNA and mature protein have been found in the gonads of a number of fish species, including Mozambique tilapia [31], Nile tilapia [91], seabream [20,95], Japanese flounder [41], goldfish [113], fugu (Takifugu rubripes) [59], and starry flounder [72], suggesting that PRL may be involved in spermatogenesis, vitellogenesis, and/or ovulation. Further studies involving immunohistochemical analyses of fish gonads across the full reproductive cycle are required to clarify these functions.…”