The second prolactin receptor in Nile tilapia (Oreochromis niloticus): molecular characterization, tissue distribution and gene expression

Identification and sequence analysis of prolactin receptor and its differential expression profile at various developmental stages in striped hamsters

Prolactin (PRL) plays critical roles in regulation of biological functions with the binding of specific prolactin receptor (PRLR). Revealing the expression patterns of PRLR at different developmental stages is beneficial to better understand the role of PRL and its mechanism of action in striped hamsters. In this study, the cDNA sequence of PRLR (2866-base-pairs) was harvested from the pituitary of mature female striped hamsters (Cricetulus barabensis) that contains an 834-base-pair 5′-untranslated region (1-834 bp), a 1848-base-pair open reading frame (835-2682 bp), and a 184-base-pair 3′-untranslated region (2683-2866). The 1848-base-pair open reading frame encodes a mature prolactin-binding protein of 592 amino acids. In the mature PRLR, two prolactin-binding motifs, 12 cysteines, and five potential Asn-linked glycosylation sites were detected. Our results showed that the PRLR mRNA quantity in the hypothalamus, pituitary, ovaries, or testis was developmental-stage-dependent, with the highest level at sub-adult stage and the lowest level at old stage. We also found that PRLR mRNAs were highest in pituitary, medium level in hypothalamus, and lowest in ovaries or testis. PRLR mRNAs were significantly higher in males than in females, except in the hypothalamus and pituitary from 7-week-old striped hamsters. Moreover, the PRLR mRNAs in the hypothalamus, pituitary, and ovaries or testis were positively correlated with the expression levels of GnRH in the hypothalamus. These results indicated that the PRLR has conserved domain in striped hamster, but also possesses specific character. PRLR has multiple biological functions including positively regulating reproduction in the striped hamster.

Osmoregulatory actions of prolactin in the gastrointestinal tract of fishes

In fishes, prolactin (Prl) signaling underlies the homeostatic regulation of hydromineral balance by controlling essential solute and water transporting functions performed by the gill, gastrointestinal tract, kidney, urinary bladder, and integument. Comparative studies spanning over 60 years have firmly established that Prl promotes physiological activities that enable euryhaline and stenohaline teleosts to reside in freshwater environments; nonetheless, the specific molecular and cellular targets of Prl in ion- and water-transporting tissues are still being resolved. In this short review, we discuss how particular targets of Prl (e.g., ion cotransporters, tight-junction proteins, and ion pumps) confer adaptive functions to the esophagus and intestine. Additionally, in some instances, Prl promotes histological and functional transformations within esophageal and intestinal epithelia by regulating cell proliferation. Collectively, the demonstrated actions of Prl in the gastrointestinal tract of teleosts indicate that Prl operates to promote phenotypes supportive of freshwater acclimation and to inhibit phenotypes associated with seawater acclimation. We conclude our review by underscoring that future investigations are warranted to determine how growth hormone/Prl-family signaling evolved in basal fishes to support the gastrointestinal processes underlying hydromineral balance.

miR-135a Targets and Regulates Prolactin Receptor Gene in Goat Mammary Epithelial Cells

Mammary gland development and lactation are typical traits controlled by multiple genes, hormones, and regulatory factors. Prolactin receptor (PRLR), a specific receptor of prolactin, has been reported to have important physiological functions in regulating mammogenesis and lactogenesis. However, the post-transcriptional regulation mechanisms of PRLR expression have not yet been shown in detail. In this study, the expression of miR-135a and PRLR at different development stages of Laoshan dairy goat mammary gland tissues was investigated. After overexpression and silencing expression of miR-135a in cultured primary mammary epithelial cells, the regulatory relationship between miR-135a and PRLR was examined through dual-luciferase reporter assay, and the expression of PRLR at both mRNA and protein levels was examined by real-time quantitative polymerase chain reaction (RT-qPCR) and western blot. Collectively, our results suggested that PRLR is a direct target gene of miR-135a, miR-135a is a novel regulator of PRLR, and it might play an essential role in the regulation of animal mammary gland development and lactation.

Effects of salinity and prolactin on gene transcript levels of ion transporters, ion pumps and prolactin receptors in Mozambique tilapia intestine

Euryhaline teleosts are faced with significant challenges during changes in salinity. Osmoregulatory responses to salinity changes are mediated through the neuroendocrine system which directs osmoregulatory tissues to modulate ion transport. Prolactin (PRL) plays a major role in freshwater (FW) osmoregulation by promoting ion uptake in osmoregulatory tissues, including intestine. We measured mRNA expression of ion pumps, Na(+)/K(+)-ATPase α3-subunit (NKAα3) and vacuolar type H(+)-ATPase A-subunit (V-ATPase A-subunit); ion transporters/channels, Na(+)/K(+)/2Cl(-) co-transporter (NKCC2) and cystic fibrosis transmembrane conductance regulator (CFTR); and the two PRL receptors, PRLR1 and PRLR2 in eleven intestinal segments of Mozambique tilapia (Oreochromis mossambicus) acclimated to FW or seawater (SW). Gene expression levels of NKAα3, V-ATPase A-subunit, and NKCC2 were generally lower in middle segments of the intestine, whereas CFTR mRNA was most highly expressed in anterior intestine of FW-fish. In both FW- and SW-acclimated fish, PRLR1 was most highly expressed in the terminal segment of the intestine, whereas PRLR2 was generally most highly expressed in anterior intestinal segments. While NKCC2, NKAα3 and PRLR2 mRNA expression was higher in the intestinal segments of SW-acclimated fish, CFTR mRNA expression was higher in FW-fish; PRLR1 and V-ATPase A-subunit mRNA expression was similar between FW- and SW-acclimated fish. Next, we characterized the effects of hypophysectomy (Hx) and PRL replacement on the expression of intestinal transcripts. Hypophysectomy reduced both NKCC2 and CFTR expression in particular intestinal segments; however, only NKCC2 expression was restored by PRL replacement. Together, these findings describe how both acclimation salinity and PRL impact transcript levels of effectors of ion transport in tilapia intestine.

Characterization of genes encoding prolactin and prolactin receptors in starry flounder Platichthys stellatus and their expression upon acclimation to freshwater

This study aims to investigate the genes encoding prolactin (PRL) and prolactin receptors (PRLR) and their tissue-specific expression in starry flounder Platichthys stellatus. Starry flounder PRL gene consisting of five exons encodes an ORF of 212 amino acid residue comprised of a putative signal peptide of 24 amino acids and a mature protein of 188 amino acids. It showed amino acid identities of 73 % with tuna Thunnus thynnus, 71 % with black porgy Acanthopagrus schlegelii, 69 % with Nile tilapia Oreochromis niloticus, 64 % with pufferfish Takifugu rubripes, 63 % with rainbow trout Oncorhynchus mykiss, and 60 % with mangrove rivulus Kryptolebias marmoratus. Phylogenetic analysis of piscine PRLs also demonstrated a similarity between starry flounder and other teleosts but with a broad distinction from non-teleost PRLs. PRLR gene consists of eight exons encoding a protein of 528 amino acid residues. It showed a similarity to the PRLR2 subtype as reflected by amino acid identities of 54 % with A. schlegelii, 48.1 % with K. marmoratus, 46.3 % with tilapia O. mossambicus, and 46.1 % with O. niloticus PRLR2 as compared to PRLR1 isoform having less than 30 % identities. While mRNA transcript corresponding to PRL was detected only from the pituitary, most of PRLR mRNA was detected in the gill, kidney, and intestine, with a small amount in the ovary. The level of PRL transcript progressively increased during 6 days of acclimation to freshwater and then decreased but stayed higher than that of seawater at 60 days of acclimation. An opposite pattern of changes including a decrease at the beginning of the acclimation but a slight increase in the level osmolality was found as adaptation continued. The results support the osmoregulatory role of PRL signaling in starry flounder.