Isolation and identification of a cDNA clone of rat placental lactogen II

Genes and signals regulating murine trophoblast cell development

A fundamental step in embryonic development is cell differentiation whereby highly specialised cell types are developed from a single undifferentiated, fertilised egg. One of the earliest lineages to form in the mammalian conceptus is the trophoblast, which contributes exclusively to the extraembryonic structures that form the placenta. Trophoblast giant cells (TGCs) in the rodent placenta form the outermost layer of the extraembryonic compartment, establish direct contact with maternal cells, and produce a number of pregnancy-specific cytokine hormones. Giant cells differentiate from proliferative trophoblasts as they exit the cell cycle and enter a genome-amplifying endocycle. Normal differentiation of secondary TGCs is a critical step toward the formation of the placenta and normal embryonic development. Trophoblast development is also of particular interest to the developmental biologist and immunobiologist, as these cells constitute the immediate cellular boundary between the embryonic and maternal tissues. Abnormalities in the development of secondary TGCs results in severe malfunction of the placenta. Herein we review new information that has been accumulated recently regarding the molecular and cellular regulation of trophoblast and placenta development. In particular, we discuss the molecular aspects of murine TGC differentiation. We also focus on the role of growth and transcription factors in TGC development.

Effects of cadmium on the expression of placental lactogens and Pit-1 genes in the rat placental trophoblast cells

Cadmium is an endocrine disrupter (ED) with detrimental effects on mammalian reproduction. The placenta is a primary target for cadmium toxicity during pregnancy. Very little of this metal crosses the placenta to the fetus, and consequently it accumulates in high concentrations in the placenta. Cadmium affects on steroid synthesis and has estrogen- and androgen-like activities. In this study, we investigated the toxic effects of cadmium on placental trophoblast cells as well as the mRNA levels of placental lactogens (PLs), which are under the control of estrogen and play a pivotal role during pregnancy. Pregnant F344 Fisher rats were injected subcutaneously with 0, 0.2, and 2.0mg/kg BW/day of cadmium (CdCl(2)) dissolved in saline from days 11 to 19 of pregnancy and were sacrificed on day 20. The mRNA levels of the PL-Iv and -II genes and Pit-1alpha and beta isotype genes, the trans-acting factor of PLs, were analyzed by Northern blot hybridization and reverse transcription-polymerase chain reaction, respectively. The frequency of the placental trophoblast cells was observed histochemically. Developmental data and apoptotic chromosomal DNA fragmentation of placental cells were also observed. The mRNA levels of PL-Iv and -II were reduced in a dose-dependent manner by cadmium. The mRNA levels of the Pit-1alpha and beta isotype genes were also reduced by cadmium. In the uterus-conjugated region of the placental junctional zone, the frequency rates of trophoblast cells were lower in the cadmium-treated groups than in the control group. High-dose cadmium exposure (2.0mg) induced not only the reduction of trophoblast cell frequency but also apoptotic chromosomal DNA fragmentation in the junctional zone of the placenta. Developmental metrics such as placental and fetal weights and a number of live fetuses, decreased, while a numbers of resorptions, dead fetuses, and post-implantation losses increased significantly (p<0.05) in the cadmium-treated groups compared to the control. These data suggested that cadmium inhibits the expression of PL genes and reduces the number of trophoblast cells in the rat placenta via an estrogen-like activity, leading to significant toxic effects on placental growth and physiological function in rats.

The rat prolactin gene family locus: species-specific gene family expansion

In the rat there is a large family of paralogous genes related to prolactin (PRL). Members of the PRL family are expressed in cell- and temporal-specific patterns in the anterior pituitary, uterus, and placenta. An overriding feature of the PRL family is its association with pregnancy. In this investigation, we used information derived from the public rat genome database as a tool for identifying new members of the rat PRL family. The entire rat PRL gene family locus spans approximately 1.7 megabases (Mb) on Chromosome 17. Genes possessed either 5- or 6-exon organization patterns. We provide information on three newly identified genes orthologous to previously identified members of the mouse PRL gene family [placental lactogen-Ialpha (PL-Ialpha), PL-Ibeta, and proliferin (PLF)] and a new member of the PRL family, termed PRL-like protein-P (PLP-P). Information is also presented on the existence of multiple PLP-M transcripts, which are generated by alternative splicing. Expansion of the PRL family has occurred independently in rodents versus the cow and does not exist in the human and dog. Elucidation of the rat PRL gene family locus provides tools for studying the genetics and biology of the rat PRL family and new insights into species-specific gene family expansion.

Trophoblast differentiation in vitro: establishment and characterisation of a serum-free culture model for murine secondary trophoblast giant cells

Differentiation of trophoblast giant cells is an early event during the process of murine embryo implantation. However, differentiation of secondary trophoblast giant cells in the rodent is still only partially understood, probably because of the lack of suitablein vitromodels and cell markers. In order to advance our understanding of trophoblast differentiation, suitablein vitromodels and markers are required to study their development. The objectives of this study were to establish and characterise a serum-freein vitromodel for murine secondary trophoblast cells. Secondary trophoblast giant cells growingin vitroand paraffin sections of day 8.5 postcoitum mouse embryos were processed for immunostaining to establish the expression of potential markers using antibodies to blood group antigens, E-cadherin, α7integrins and activator protein-γ, as well as placental lactogen-II. Within 3 days in serum-free culture, ectoplacental cone-derived secondary trophoblast cells underwent simultaneous induction of both morphological and functional differentiation. Secondary trophoblasts grewin vitroas a monolayer of cells with giant nuclei and expressed B and Le-b/Le-y blood group antigens, α7integrins and placental lactogen-II, as well as activator protein-γ. Transcripts for activator protein-γ and placental lactogen-II were detected in cultures by RT-PCR and for placental lactogen-II byin situhybridisation. At later time-points apoptosis increased. A fibronectin substrate significantly increased secondary trophoblast cell numbers and surface area of outgrowth. The increase in cells with giant nuclei coincided with induction of placental lactogen-II expression. A relationship was found between the nuclear area of secondary trophoblast cells and expression of placental lactogen-II.

Circadian expression of Mel1a and PL-II genes in placenta: effects of melatonin on the PL-II gene expression in the rat placenta

In the mammal, melatonin regulates the seasonal and/or circadian rhythm of PRL levels. Since several members of the PRL gene family are expressed during late pregnancy, we investigated the relationship between the expression of placental lactogen (PL)-II-one member of the PRL family- and melatonin, as well as the placental expression of one of the receptors for melatonin, melatonin receptor 1a (Mel(1a())). Herein we provide the first demonstration that Mel(1a) is not only expressed in the rat placenta, but that it is spatially and temporally regulated throughout late pregnancy. In situ hybridization and Northern blot analyses show that Mel(1a) mRNA is localized in the rat placenta on gestational day 19, and is mainly restricted to the spongiotrophoblast and trophoblast giant cells. Interestingly, the junctional zone of the placenta at this time showed the strongest gene expression when the tissue was obtained at 16:00 h (daytime) and showed the least expression when it was obtained at 04:00 h (night-time). In contrast, the labyrinth zone showed the strongest expression in tissue obtained at night and showed the least expression in tissue obtained during the day. PL-II gene expression also exhibited a circadian rhythm but the direction of the fluctuation was exactly opposite to that of the Mel(1a) gene, such that at night the junctional zone had the strongest expression, while the labyrinth zone had the weakest. In vitro treatment of placental tissue with an melatonin agonist, chloromelatonin, greatly decreased PL-II mRNA levels. That Mel(1a) plays a regulatory role in the expression of PL-II in the late-pregnancy rat placenta is strongly suggested by the pattern of its own spatial and temporal expression.

The mouse prolactin gene family locus

In the mouse, there is a large family of paralogous genes closely related to PRL. The objective of this report was to investigate the organization of the mouse PRL gene family locus. PRL family genes reside on chromosome 13 of the mouse genome. The PRL gene family members were localized to a series of overlapping bacterial artificial chromosome clones and arranged based on structural relationships. Additionally, several new members of the PRL gene family were identified. Placental lactogen I (PL-I) was found to be encoded by three closely related (>98% exon sequence identity) contiguous genes (termed: PL-Ialpha, PL-Ibeta, and PL-Igamma). Two previously unidentified mouse orthologs for members of the rat PRL family, PRL-like protein-I (PLP-I) and PLP-K were discovered, as were two new members of the PLP-C subfamily, PLP-Cgamma and PLP-Cdelta, and two new entirely unique members of the PRL family, PLP-N and PLP-O. Amino acid sequences predicted from the latter two genes most closely resembled proliferin-related protein. Each of the nine newly discovered genes is expressed in trophoblast cells of the mouse placenta in a gestationally specific pattern. In summary, elucidation of the mouse PRL gene family locus provides new insights into the expansion of the mouse PRL family and new tools for studying the genetics and biology of its members.

Identification of three prolactin-related hormones as markers of invasive trophoblasts in the rat

An expressed-sequence tag database search has identified three rat cDNA clones in the prolactin/growth hormone family, including a homologue of mouse proliferin-related protein (PRP). The encoded proteins of the two novel clones, designated prolactin-like proteins L (PLP-L) and M (PLP-M), are predicted to be synthesized as precursors of 229 and 227 amino acids, modified by N-linked glycosylation, and secreted as mature glycoproteins of 199 and 200 residues, respectively. Murine homologues to PLP-L and PLP-M were also identified. The open reading frame of rat PRP encodes a precursor protein of 245 amino acids and predicts a secreted 215-amino acid glycoprotein with 81% identity to mouse PRP. All three rat mRNAs are expressed in the placenta, and expression is not detected in other tissues. PLP-L mRNA expression is observed from Days 11-20, with highest levels at Day 13; highest levels of PLP-M are observed from Day 11 until parturition, with peak levels also on Day 13; and highest levels of PRP are also observed from Day 11 until term, with maximal expression on Day 17. All three genes are most highly expressed in invasive trophoblast cells lining the central placental vessel. The identification of molecular markers for endovascular trophoblasts serves to highlight the invasive nature of rodent placentation and may prove useful for future studies of placental function.

Constitutive expression of placental lactogen in pancreatic beta cells: effects on cell morphology, growth, and gene expression

To explore the roles of lactogens in islet function, we generated a stable line of rat insulinoma (INS-1) cells that express rat placental lactogen II (rPLII) constitutively in culture. We used this cell line (Ins-rPLII) to examine the effects of endogenous rPLII on beta-cell growth, islet formation, and the expression of glucose transporter 2 (glut-2) and insulin mRNA. Growth and maturation of Ins-rPLII cells were compared with that of cells transfected stably with an empty expression plasmid (control) and of INS-1 cells treated with exogenous prolactin. The Ins-rPLII cells proliferated more rapidly than control cells in serumfree medium and showed distinct morphologic characteristics in culture. Whereas the control cells flattened readily on plastic and formed a branching monolayer, the Ins-rPLII cells remained more rounded, sent out fewer projections, and formed more numerous (p<0.01) and larger (p<0.01) beta-cell clusters. Larger clusters assumed a spherical form with well-delineated smooth borders and detached more readily from the culture plates. Maturational progression of the Ins-rPLII cells was associated with a 40% increase in preproinsulin mRNA (p<0.05) and a 2-3-fold increase in glut-2 mRNA (p<0.01). Induction of glut-2 mRNA was accompanied by a 1.4-2.4-fold increase (p< 0.01) in the uptake of radiolabeled 2-deoxyglucose. Similar effects were observed in INS-1 cells exposed for 48 h to exogenous prolactin. These findings suggest novel roles for the lactogenic hormones in the maturation and growth of pancreatic islets. Lactogen induction of beta-cell aggregation coupled with localized beta-cell growth may contribute to the expansion of islet mass that occurs in pregnancy and during the perinatal period. The induction of insulin and glut-2 mRNA provides a mechanism by which the lactogens may increase fetal and maternal insulin production and enhance the sensitivity of the pancreas to glucose.

Prolactin (PRL)-like protein J, a novel member of the PRL/growth hormone family, is exclusively expressed in maternal decidua

A search of a nonmouse, nonhuman, expressed sequence tag database for messenger RNAs in the PRL/GH family has identified a novel rat complementary DNA clone. The encoded protein, designated PRL-like protein J (PLP-J), is predicted to be synthesized as a precursor of 211 amino acids, modified by N-linked glycosylation, and secreted as a mature glycoprotein of 182 residues. PLP-J messenger RNA synthesis is limited to early pregnancy with abundant expression on day 7, slightly declining expression on day 9, and no detectable expression by day 11. Unlike most other PRL family members, PLP-J does not appear to be synthesized by placental trophoblasts but, rather, by decidual cells surrounding the implantation site. By sequence similarity to rat PLP-J, a murine clone was identified in a mouse expressed sequence tag database. Mouse PLP-J was used to map the gene to a 700-kb region of mouse chromosome 13 that includes other members of the PRL/GH family.

PLP-I: a novel prolactin-like gene in rodents

In this report, we describe molecular cloning and characterization of cDNAs encoding a novel rat prolactin-like protein. The rat cDNAs were isolated from the decidua and the gene was named PLP-I. cDNAs for the mouse equivalent were also cloned by the cross-hybridization technique. Pregnancy-specific expression of the rat PLP-I gene was observed in the rat placenta by Northern analysis. Location of signal peptide cleavage sites in rat and mouse pre-PLP-I proteins was predicted using a theoretical method. A molecular phylogenetic tree for the growth hormone-prolactin superfamily including the novel member, PLP-I, constructed using the neighbor-joining method, places rat/mouse PLP-I closest to rat/mouse placental lactogen I and II.

Endothelial cell chemotaxic activity expressed in rat placenta is not associated with prolactin-like proteins B and C

Conditioned medium from gestation day 18 rat placental cultures showed potent stimulation of the directional migration of human retinal endothelial cells. To examine the role of major secreted placental proteins in this chemotaxic activity, prolactin-like proteins (PLPs)-B and C were purified from rat placenta using immuno-affinity chromatography. In contrast to conditioned medium, native PLP-B and PLP-C preparations failed to show any significant stimulation of endothelial cell migration. This study further examined the ability of PLP-B to bind to rat receptors for growth hormone (GH-R) and prolactin (PRL-R). In competitive binding assays with [125I]-hGH, neither native nor recombinant PLP-B preparations showed significant high affinity binding to the transfected rat GH-R or PRL-R. In summary, neither PLP-B nor PLP-C exhibit the potent chemotaxis stimulatory activity of placental conditioned media, nor does PLP-B show evidence of ability to act via rat GH or PRL receptors.

Identification of two new members of the mouse prolactin gene family

The prolactin (PRL) family consists of a collection of genes expressed in the uterus, placenta, and anterior pituitary. These cytokines/hormones participate in the control of maternal-fetal adaptations to pregnancy. In this report, we establish the presence of two new members of the mouse PRL family. Novel expressed sequence tags (ESTs) with significant homology to PRL were isolated from embryonic, ectoplacental cone, and placental cDNA libraries. The cDNAs were sequenced and compared to other members of the PRL family. The two new cDNAs were assigned to the PRL family based on sequence homology and were referred to as PRL-like protein-F (PLP-F) and PRL-like protein-G (PLP-G). PLP-F cDNA encodes for a predicted 267 amino acid protein containing a 30 amino acid signal peptide and three putative N-linked glycosylation sites. PLP-G cDNA encodes for a predicted 266 amino acid protein containing a 30 amino acid signal peptide and six putative N-linked glycosylation sites. Sequence alignments of these proteins with other members of the PRL family suggest some unique features. Both sequences contain an extra amino acid segment located between exons two and three of the prototypical PRL gene and a nine amino acid carboxy terminal extension. PLP-F contained an additional 15 amino acid region situated between exons four and five of the prototypical PRL gene. Both PLP-F and PLP-G mRNAs were expressed in the placenta but not in other tissues (uterus, brain, thymus, heart, lung, diaphragm, liver, kidney, and ovary). In summary, the two newly identified members share approximately 50% amino acid sequence identity, are specifically expressed in the placenta, and represent a new subfamily within the PRL family.

Rat placental lactogen II gene: characterization of gene structure and placental-specific expression

Rat placental lactogen II (rPLII) was the first described member of the rat PRL-like placental gene family in which nine novel proteins have now been identified. In this article, we present data on the isolation and characterization of the rPLII gene. Two genomic clones, GC I (18.5 kb) and GC II (9.4 kb), were isolated from an EMBL3 Sprague-Dawley rat liver genomic DNA library. GC I, which was used for further analysis, contains the entire coding region and extensive 5' and 3' flanking information. The rPLII gene, estimated to be 5.4 kb in size, has the same five-exon and four-intron structure and identical intron/exon splice sites and types as the rPRL gene. A major transcription start site 58 bp upstream of the initiator methionine codon and several minor sites 1-3 bp 5' and 3' of this site were identified by primer extension of day 18 placental messenger RNA. The rPLII gene has been localized to chromosome 17, using a series of hybrid cell lines derived from mouse hepatoma cells (MWTG3) and adult rat hepatocytes; this is the same chromosome designation as the PRL gene itself and other cloned placental members of this gene family. Luciferase reporter constructs containing 5' flanking DNA sequences were tested in transient transfection assays in the rat choriocarcinoma cell line, Rcho, and the rat pituitary GC cell line. Both a 4.5- and 3-kb 5' flanking sequence supported luciferase expression in the Rcho but not the GC cells. A 765-bp fragment showed no activity in either cell type. Transient transgenic mice, generated with the 3-kb 5' rPLII/luciferase construct, expressed varying amounts of luciferase expression in the placenta.

Two novel members of the prolactin/growth hormone family are expressed in the mouse placenta

Two novel members of the mouse PRL/GH family have been identified through a search of an expressed sequence tag database. The encoded proteins do not appear to be homologs of other known members of this hormone family. One of these proteins, designated PRL-like protein E (PLP-E), is predicted to be synthesized as a precursor of 265 amino acids, modified by N-linked glycosylation, and secreted as a mature glycoprotein of 236 residues. The second clone encodes a protein of 253 residues with consensus sites for N-linked glycosylation; the secreted form of the protein, designated PRL-like protein F (PLP-F), is predicted to be 223 amino acids in length. Both of these messenger RNAs are expressed specifically in the placenta, with peak levels of PLP-E on days 10-12 and of PLP-F on days 14-16. Expression of PLP-E is restricted to the trophoblast giant cells, whereas PLP-F is synthesized only in the spongiotrophoblasts. The genes for both of these proteins map to a 700-kilobase region of mouse chromosome 13 that includes other members of the PRL/GH family.

Rat placental lactogens initiate and maintain lactation yet inhibit suckling-induced prolactin release

Mammalian reproduction is dependent on both a successful pregnancy and on the subsequent period of lactation. In the rat, ovulation occurs shortly after parturition making it possible for a dam to be simultaneously pregnant and lactating. The present studies investigate the effect of placental hormones on suckling-induced prolactin (PRL) release and the contribution of placental hormones to milk synthesis and secretion. A rat choriocarcinoma cell line, Rcho-1, which secretes placental lactogens (PLs) following transplantation in vivo, attenuated suckling-induced PRL release on both d 9 and d 14 of lactation by 43 and 58%, respectively. When PRL secretion was completely inhibited by bromocriptine, a dopamine agonist, Rcho-1-bearing dams still maintained a normal litters weight gain, demonstrating that placental lactogens can continue an established lactation. The Rcho-1 tumors also initiated milk synthesis and secretion in nulliparous rats continuously exposed to pups. Whereas none of the 11 control virgins began lactating and had an average pup weight loss of 2.07 g, the Rcho-1-bearing rats began lactating, as evidenced by a significant reduction in pup weight loss. Thirty percent of these rats became fully lactationally competent. Northern blot analysis showed that the Rcho-1 tumors expressed both PL-I and PL-II mRNA in all experimental groups. These tumors also secreted PL-I into the circulation, as shown by radioimmunoassay.

Placental lactogen-I variant utilizes the prolactin receptor signaling pathway

Placenta lactogen-I variant (PL-Iv) is a member of a family of proteins expressed by the rat placenta with characteristics similar to prolactin (PRL). In this report, we present the molecular cloning, chromosomal localization, and heterologous expression of PL-Iv. Nucleotide sequence analysis of the PL-Iv cDNA clone predicted a precursor protein of 223 amino acids, including a 28-amino acid signal sequence. The PL-Iv gene was localized to chromosome 17 of the rat genome, which also carries other members of the PRL gene family. PL-Iv heterologously expressed in Chinese Hamster ovary (CHO) cells exhibited similar immunoreactive and electrophoretic characteristics with PL-Iv produced by the rat placenta. N-terminal sequencing verified the identity and purity of the recombinant PL-Iv species and the site of cleavage of the signal peptide from the mature secreted PL-Iv species. Recombinant PL-Iv was shown to bind to ovarian and liver PRL receptors, stimulate the proliferation of Nb2 lymphoma cells, and activate Jak2. Each of these actions is consistent with PL-Iv utilizing the PRL receptor signal transduction pathway.

Cloning of a novel rat placental prolactin-like protein C-related cDNA

Prolactin-like protein C (PLP-C) is a major rat placental protein which is expressed during the second half of pregnancy and belongs to the growth hormone-prolactin family. Here we report on the isolation of overlapping rat placental cDNAs which specify a transcript of 915 base pairs and predict a 205-amino acid translated product. The full-length cDNA shares 93% homology with the nucleotide sequence reported for PLP-C, and the putative protein, which we designate PCRP (prolactin-like protein C-related protein), exhibits 88% homology with the PLP-C precursor protein. PCRP lacks the signal sequence and the first 2 N-terminal cysteine residues present in PLP-C. Northern blot analysis indicated the basal zone-specific expression of PCRP mRNA, with no detectable expression in decidua and labyrinth. Southern blot analysis of rat genomic DNA using PCRP cDNA as a probe demonstrated multiple hybridization bands, suggestive of a family of genes encoding prolactin-like proteins. Western immunoblot analysis of basal zone culture media using a PCRP antipeptide antiserum revealed at least 5 immunoreactive proteins. The existence of a PLP-C family of proteins in rat placenta after midpregnancy suggests their functional significance in the maintenance of pregnancy and fetal development.

Expression and characterization of recombinant rat placental prolactin-like protein C

Prolactin-like protein C (PLP-C) is a member of the rat placental family of proteins which are structurally related to pituitary prolactin (PRL). In an effort to characterize the receptor specificity and biological activity of PLP-C, we used a PLP cDNA to express the recombinant protein in a bacterial system. The PLP-C cDNA was modified by oligonucleotide mutagenesis and ligated into a human carbonic anhydrase II (hCAII) expression vector. Following a single step affinity purification, the hCAII-PLP-C fusion protein was digested with enterokinase to release a 25 kDa protein. N-Terminal sequence analysis of the 25 kDa band demonstrated identity with PLP-C. A polyclonal antiserum to the fusion protein cross reacted with seven major proteins in rat placental culture media of which two were the native forms of PLP-C. Recombinant PLP-C was not mitogenic in the Nb2 lymphoma bioassay and did not exhibit high affinity binding to rat PRL receptor. The choice of hCA-II fusion allows for rapid purification of rPLP-C which will aid in further investigation of the biological role of PLP-C.

Rat prolactin-like protein A partial gene and promoter structure: promoter activity in placental and pituitary cells

Rat prolactin-like protein A (rPLP-A) is a member of a rapidly expanding family of prolactin-related proteins that are expressed during pregnancy by the rat placenta according to specific developmental patterns. Although the factors involved in the pituitary-specific expression of the prolactin and growth hormone genes themselves have been extensively studied, essentially nothing is known of the factors responsible for the placental expression of these new family members. In this paper we describe the isolation of rPLP-A genomic clones, analyze a portion of the 5' flanking sequence of this gene and use the recently described rat choriocarcinoma cell line, Rcho, in transient transfection studies to show that a 975 base-pair (bp) fragment of 5' flanking sequence is sufficient to specify placental expression of the rPLP-A gene.

Somatic cell mapping, polymorphism, and linkage analysis of bovine prolactin-related proteins and placental lactogen

The bovine prolactin gene family includes novel members expressed in the fetal placenta that are distinct from placental lactogen. In this study, we investigated the genetic organization of four members of this gene family (PRP1, PRP3, PRP6, and PRP10) as well as placental lactogen (PL). Using a bovine-rodent hybrid somatic cell panel, all five genes were assigned to bovine chromosome 23, which contains prolactin and the major histocompatibility group (BOLA). Restriction fragment length polymorphisms were detected by all probes in breeding populations with the restriction enzyme MspI, whereas no polymorphisms were detected with BamHI. EcoRI, HindIII, TaqI, and PstI produced polymorphic fragments with some but not all of the probes tested. A PRP10 polymorphism, which is apparently the result of a insertion/deletion event, detected polymorphism frequency differences between Bos indicus and Bos taurus. No recombinational events were observed with these probes and prolactin using linkage analysis involving 91 American Holsteins. The bovine prolactin gene family was incorporated into a linkage group containing CYP21. Our studies demonstrate that members of the bovine prolactin gene family have a close physical association with each other, and all members demonstrate genetic variability in the breeding population.

Multiple forms of rat placental lactogen-II (rPL-II): purification and partial characterization of rPL-II

The present study was designed to develop a procedure for purifying rPL-II and a homologous radioimmunoassay (RIA) for rPL-II. Molecular profiles of rPL-II were also investigated in tissue and plasma. rPL-II was purified 3,780-fold, based on its radioreceptor assay (RRA) activity compared to ovine prolactin (0PRL), from the placenta of day 18 pregnant rats using ammonium sulfate precipitation and chromatography on phenyl-Sepharose, DEAE-TOYOPEARL 650S, AF-chelate TOYOPEARL 650M and Sephadex G-100. Electrophoretic analysis on SDS gel revealed molecular weight heterogeneity of purified rPL-II, which consisted of three proteins; a major form with a molecular weight of 20.0 K and two minor forms with molecular weights of 20.6 K and 21.0 K under non-reducing conditions. One of the minor forms of rPL-II observed under non-reducing conditions disappeared with 2-mercaptoethanol treatment and the rest of the hormones migrated as 24.5 K and 25.0 K molecular weight species, suggesting that it is a cleaved form of rPL-II. Purified rPL-II displaced 125I-labelled oPRL from binding sites on rabbit mammary gland membranes in a dose-dependent manner. rPL-II and rPRL were, respectively, 21 and 2 per cent as effective as oPRL in the displacement. Antibody to purified rPL-II was raised in rabbits and a homologous RIA for rPL-II was developed. No displacement was observed with rPRL, rGH, oPRL, and other pituitary hormones up to 1,000 ng/ml. Molecular profiles of rPL-II in the placental tissue and plasma from day 18 pregnant rats were examined by gel chromatography on Sepharcryl S-300 HR and by Western blotting. Chromatography of the placental extracts revealed a single peak, which accounted for 86 per cent of the total RIA activity. Anti-rPL-II antiserum detected proteins of at least three molecular sizes as monomeric forms with molecular weights of 20.0, 20.6, and 21.0 K in the non-reducing placental extracts. One of them disappeared with 2-mercaptoethanol treatment and other two proteins had molecular weights of 24.5 and 25.0 K, indicating monomeric heterogeneity of rPL-II in the tissue. The elution profile of day 18 plasma in RIA activity gave two major peaks; the first, eluting just after the void volume (approximate molecular weight of 530 K) accounted for 35 per cent of the total RIA activity, and the second coinciding with the same elution volume as the monomeric form in the placental extract constituted about 26 per cent of the total RIA activity.(ABSTRACT TRUNCATED AT 400 WORDS)

A novel cDNA clone encoding a prolactin-like protein that lacks the two C-terminal cysteine residues isolated from bovine placenta

A new prolactin-like cDNA clone, bPLP-IV, was isolated from a bovine placental cDNA library and the complete nucleotide sequence was determined. The bPLP-IV encodes a protein consisting of 237 amino acids, which is related to, but different from seven other known bovine prolactin-like proteins including two placental lactogens. The predicted amino acid sequence of the bPLP-IV shows over 52% identity to other known members of bovine prolactin-like proteins, 48% to bovine prolactin, 40% to both two bovine placental lactogens and only 22% to bovine growth hormone. The bPLP-IV protein has a unique feature in its primary structure, lacking the two C-terminal cysteine residues which are completely conserved in all other known members of prolactin-growth hormone-placental lactogen gene family. The expression of bPLP-IV in developing bovine placenta was apparently stage-specific, being maximal in the full-term placenta.

Characterization of placental prolactin-like protein-A in intracellular and extracellular compartments

Prolactin-like protein-A (PLP-A) was purified from medium conditioned by junctional zone explants dissected from the rat chorioallantoic placenta via concanavalin A affinity chromatography, sodium dodecyl sulfate-gel electrophoresis and two-dimensional gel electrophoresis. Monomeric PLP-A was found to be heterogeneous and consisted of two major molecular sizes, 29 and 33 kDa. The charge and size heterogeneity attributed to monomeric PLP-A could be accounted for by the addition of N-linked carbohydrate moieties to the PLP-A structure. Monomeric PLP-A lacked lactogenic bioactivities and several attempts to sequence 29 and 33 kDa PLP-A monomers proved unsuccessful. Biochemical characterization of PLP-A species present in various intracellular and extracellular compartments indicated that PLP-A is normally secreted as high molecular weight complexes and that PLP-A species were also targeted to the nucleus. PLP-A species isolated from placental cytosol or from serum of pregnant rats predominantly circulated as disulfide-linked high molecular weight complexes. PLP-A antipeptide antisera showed limited but specific reactivity with the high molecular weight PLP-A species. We have specifically identified a 29 kDa protein species in placental cell nuclei with three antibodies directed to three different regions of the predicted amino acid sequence of PLP-A. The 29 kDa nuclear immunoreactive protein had an equivalent electrophoretic mobility to the 29 kDa PLP-A protein of junctional zone cytosol. The 33 kDa PLP-A protein was not identified in the nucleus. The biological significance of the circulating high molecular weight PLP-A species or the nuclear PLP-A species remains to be determined.

Ontogeny of placental lactogen-I and placental lactogen-II expression in the developing rat placenta

The purpose of this investigation was to identify the cellular origin, and the temporal and regional characteristics of placental lactogen-I (PL-I) and placental lactogen-II (PL-II) expression during placental development in the rat. PL-I and PL-II mRNA expression were assessed by Northern blot analysis and in situ hybridization. PL-I and PL-II protein expression were determined by Western blot and immunocytochemical analyses. PL-I mRNA was first detected by in situ hybridization at Day 6 of gestation in mural trophoblast giant cells and a day later, PL-I protein was first detected by immunocytochemistry. PL-I immunostaining extended to the polar trophoblast giant cells as gestation advanced. Polar trophoblast giant cell staining for PL-I was not as intense as the mural trophoblast giant cell staining. Northern and Western blot analyses confirmed the asymmetric distribution of PL-I expression. PL-I mRNA migrated as a 1-kb species and PL-I protein migrated as 30- and 36-40-kDa forms. PL-I expression abruptly declined at Day 12, and by Day 13, PL-I was not detectable. PL-II protein was first detectable at Day 11 of gestation and was localized to trophoblast giant cells. PL-II mRNA could be detected at Day 10 of gestation. Northern and Western blot analyses indicated that PL-II expression significantly increased as gestation advanced and that PL-II expression was asymmetrically distributed similar to PL-I. PL-II mRNA migrated as a 1-kb species and PL-II protein migrated as a 25-kDa species. Blastocysts recovered on Day 4 of gestation initially showed no detectable expression of PL-I or PL-II; however, after 2 days of culture PL-I protein expression was detectable. Biochemical characteristics of PL-I synthesized and secreted by blastocyst outgrowths were similar to PL-I synthesized and secreted by Day 10 placental explants. In summary, (1) PL-I and PL-II are produced by trophoblast giant cells of the developing placenta, (2) PL-I and PL-II exhibit distinct temporal and regional patterns of expression during placental morphogenesis, and (3) PL-I expression by blastocyst outgrowths can be induced in vitro, whereas a more complex array of signals appears necessary for induction of PL-II expression.

Synthesis and secretion of ovine placental lactogen and its biochemical properties

The biochemical properties of ovine placental lactogen (oPL) have been previously determined following purification, which has yielded various results. To clarify the properties of oPL prior to purification, oPL was examined in solubilized fetal cotyledonary tissue (d 100 of gestation) or conditioned culture medium by electrophoretic, immunoblotting and immunoprecipitation techniques. In cotyledonary tissue or conditioned culture medium, oPL has an apparent molecular weight (Mr) of 22,000 with an isoelectric point (pI) of 9.2. Incorporation of [3H]-glucosamine or [3H]-mannose into immunoreactive oPL could not be detected, nor did the presence of tunicamycin in explant culture medium alter the apparent Mr of oPL. In vitro translation of d 100 fetal cotyledonary mRNA, followed by immunoprecipitation, provided evidence that pre-oPL has an apparent Mr of 25,000. The size of oPL mRNA was determined to be approximately 1,350 base pairs by Northern hybridization procedures using an oligonucleotide probe which was generated from oPL amino acid sequence data. These experiments suggest that the only intracellular processing oPL undergoes is removal of a amino-terminal signal sequence. We conclude that oPL is synthesized and secreted as a single nonglycosylated-basic protein, at a time during gestation when circulating oPL is elevated.

Prolactin and related peptides in pregnancy

This brief review has attempted to portray the complex involvement of prolactin in pregnancy. Pituitary prolactin production and lactotroph proliferation are markedly affected by oestrogens and pregnancy. Enlargement of pre-existing prolactinomas may occur during pregnancy induced with dopamine agonist drugs, and this can be a major clinical problem with larger tumours. Prolactin is produced by late luteal and decidualized endometrium as well as by the pituitary gland, but much less is known about its secretory regulation or its function. The family of prolactin-related protein hormones is rapidly expanding with the recognition of placental lactogens, variant growth hormone, proliferin, decidual luteotropin, and at least two further prolactin-related peptides in rodents. This complex system of related but distinct protein hormones, with different temporal patterns of production during gestation, suggests an important physiological role, but it remains to be seen to what extent they are involved in placental function itself, maternal metabolism or fetal growth.

Cellular localization of rat placental lactogen II and rat prolactin-like proteins A and B by in situ hybridization

In situ hybridizations using 35S-labelled antisense and sense RNA probes of rPLII, rPLP-A and rPLP-B were carried out on developing rat placenta to determine which cell types synthesized each specific mRNA. Cellular localization of the sites of synthesis of these placental RNAs would help to decide whether these proteins were functioning in the mother of the fetus. The cells of the basal zone are known to have access only to the maternal blood supply, while the labyrinth region is supplied by both maternal and fetal blood vessels. The data in this paper show that at day 12 of pregnancy the rPLII mRNA is synthesized in the primary and secondary giant cells. At later days, hybridization is seen in both the giant cells of the basal zone, and cells in the labyrinth, suggesting that rPLII has a function not only in the mother, but also in the fetus. The rPLP-A mRNA is synthesized in both the giant cells and the cytotrophoblasts of the basal zone. No hybridization is seen to any cells in the labyrinth, even at the later days when it appears that all cytotrophoblasts synthesize rPLP-A mRNA. The rPLP-B mRNA is synthesized exclusively by the cytophoblasts of the fetal placenta. Like rPLP-A, all these cells synthesize this mRNA in the late term placenta. The synthesis of the rPLP-A and rPLP-B mRNAs in cells which have access only to the maternal circulation suggest that they have a role in the mother.

Regulation of cell-type-specific transcription and differentiation of the pituitary

The transcription of rat prolactin and growth hormone genes in vitro requires a pituitary transcription factor, specific to certain cell types in the pituitary, which currently appears to be the PUF-I/Pit-1/GHF-1 protein. This factor binds to cis-regulatory elements in the 5' region of both genes and exerts a positive influence on transcription initiation presumably by interacting with general transcription factors. The PUF-I/Pit-1/GHF-1 transcriptional regulatory protein probably has an important role in not only the differentiation of the pituitary lactotroph/somatotroph cell lineage; it is also expressed in the early development of the nervous system but its function there is less well documented. It appears to be one member of a family of trans-activator proteins involved in differential gene expression in several cell types.

Isolation of a novel prolactin-like cDNA clone from bovine placenta: occurrence of new family members

A novel cDNA clone that hybridized to bovine prolactin cDNA was isolated from a bovine (Bos taurus) placental cDNA library and the nucleotide sequence was analyzed. The cDNA clone, named bPLP-III, contained one open reading frame encoding a protein consisting of 239 amino acids. The amino-acid sequence of bPLP-III is 43 and 57% homologous to bovine preprolactin and a bovine prolactin-related protein, bPRC-I, respectively, but only 23% homologous to bovine pregrowth hormone. The predicted mature protein of bPLP-III is distinct from bovine placental lactogens in amino-acid composition, suggesting that bPLP-III is the clone for a new member of prolactin-related mRNA expressed in bovine placenta.

Antipeptide antibodies reveal structural and functional characteristics of rat placental lactogen-II

The purpose of this investigation was to develop specific immunologic probes to rat placental lactogen-II (PL-II) and to use the immunologic probes to further characterize rat PL-II. Five oligopeptides corresponding to different regions of rat PL-II (amino acids 1-13, 56-70, 89-103, 107-118, 150-164) were chemically synthesized by solid phase methods and purified to homogeneity by reverse phase high performance liquid chromatography. The synthetic peptides were coupled to keyhole limpet hemocyanin (KLH) and the peptide-KLH conjugates were used to immunize rabbits. Antibody production was monitored by enzyme-linked immunoassay (EIA), electrophoresis and immunoblotting analyses. Each of the antipeptide antisera showed reactivity with the entire rat PL-II protein; however, the extent of the reactivities of each antiserum with rat PL-II was dependent on the conformational state of rat PL-H. Antisera directed to amino acids 56-70 showed the best reactivity toward each of the conformational states of rat PL-II tested. Antibodies generated to the entire rat PL-II protein specifically recognized the 56-70 amino acid sequence but showed limited reactivity with synthetic peptide corresponding to amino acids 1-13, 89-103, 107-118, and 150-164 of rat PL-II. Antisera to amino acids 56-70 of rat PL-II were specific for PLs as demonstrated by their recognition of rat PL-II, mouse PL-II and human PL and by their lack of reactivity with rat pituitary prolactin and growth hormone and with a series of other synthetic peptides to rat PL-II and rat prolactin-like protein-A. The immunorecognition of human PL was restricted to antipeptide antibodies directed to amino acids 56-70 of rat PL-II. The chemically synthesized peptides representing various regions of rat PL-II did not show significant interactions with prolactin receptors, and antisera directed to the peptides failed to interfere with the binding of either rat PL-II or human PL to prolactin receptors. In summary, we have generated a series of immunologic probes for studying the structure of rat PL-II. The sequence comprising amino acids 56-70 of rat PL-II was shown to make up at least part of an epitope for rat PL-II and to be a region of significant structural homology with mouse PL-II and human PL.

Pituitary-specific factor binding to the human prolactin, growth hormone, and placental lactogen genes

The human genes coding for growth hormone (GH), chorionic somatomammotropin (placental lactogen, CS), and prolactin (Prl) are related evolutionarily but are expressed in phenotypically distinct cell types despite their nucleotide sequence homology. We show here that the promoters of the human Prl and CS genes contain cis-acting sequences that confer pituitary-specific expression in a cell-free transcription assay. Similar data are obtained with the human GH gene, consistent with earlier work by others. Footprinting analysis shows that neighboring sequences in each of these three promoters are protected from deoxyribonuclease I digestion by rat pituitary cell extracts. Footprinting competition experiments and gel retardation assays with synthetic oligonucleotides suggest that a single factor is responsible for the pituitary-specific footprints seen on the human Prl, CS, and GH genes. They also suggest that this factor is identical or closely related to the trans-acting factor GHF-1/Pit-1. Similarities with and differences from the rat GH and Prl genes are discussed.

Heterogeneity of immunoreactive prolactin in the rat brain

Three immunoreactive prolactin proteins (24 Kd, 16 Kd, and 12 Kd) were identified in the rat brain using sodium dodecyl sulphate polyacrylamide gel electrophoresis, and western blot analyses. In male and female brains, the primary prolactin protein has a molecular weight of 24 Kd which is similar to that of pituitary prolactin. Two additional proteins with apparent molecular weights of 16 Kd and 12 Kd were also identified and were found in greater concentrations in the brain than in the pituitary, and were more predominant in the female brain. In addition, brain extracts proteolytically modify the 24K dalton PRL resulting in the formation of two fragments with apparent molecular weights of 16 and 8 Kd. These data indicate that the prolactin identified in the rat brain is similar to pituitary prolactin, and suggests, that like other PRL target tissues the brain may have the capacity to proteolytically modify prolactin.

Immunological studies of rodent placental lactogens

Structural relationships among the placental lactogens (PLs) from the mouse, the rat, and the hamster were examined by evaluating the cross-reactions between the PLs with a polyclonal antiserum to each PL. Two techniques, competitive radioimmunoassay displacement curves and immunoblotting of SDS-polyacrylamide gels, were used to evaluate the cross-reactions. By the first technique, a greater general similarity is found between mouse PL and rat PL than between either of these hormones and hamster PL. In contrast, the immunoblotting technique shows a greater similarity between mouse PL and hamster PL than between either of these hormones and rat PL. In the radioimmunoassays, the antibodies are reacting with the three-dimensional surfaces of the native PLs, while in the immunoblots the PLs have been denatured and unfolded. Thus, the different cross-reactions found by the two methods may reflect a dichotomy between the relationships in the primary and tertiary structures of the rodent PLs. Incomplete displacement by rat PL in the mouse PL radioimmunoassay suggests that mouse PL and hamster PL appear to share at least one surface feature that is completely absent on rat PL. All three anti-PL antisera react with multiple molecular weight bands in preparations of mouse PL and rat PL (but not hamster PL), indicating that mouse PL and rat PL are composed of several different molecular weight species while hamster PL consists of a single molecular weight form.

The human growth hormone gene locus: structure, evolution, and allelic variations

Genomic clones containing the closely related genes for human growth hormone (hGH) and chorionic somatomammotropin (hCS) were obtained from genomic bacteriophage lambda and cosmid libraries. The entire GH/CS chromosomal locus was reconstructed utilizing overlapping restriction fragments characterized from the isolated clones. The hGH/hCS locus contains two GH genes and three CS genes spanning 48 kb of DNA in the order: 5'-(hGH-1/hCS-5/hCS-1/hGH-2/hCS-2)-3', confirming analysis of cosmid clones obtained from a different human library (Barsh et al., 1983). To complete the characterization of the hCS genes, the nucleotide sequence of the hCS-5 gene was determined. Sequence analysis revealed a mutation of the 5' splice site at the exon II-intron B boundary, suggesting that the hCS-5 gene is a pseudogene. The nucleotide sequence of an allelic variant of the hCS-2 gene was determined and found to contain a single amino acid substitution and the deletion of a single codon. The hGH/hCS gene locus was further characterized by the localization of at least 27 Alu-type repetitive sequences and identification of three unique sequences in the vicinity of several hGH and hCS genes which define the probable breakpoints of the evolutionary duplication units. These data, combined with the nucleotide sequences of all five GH and CS genes, indicate that the hGH/hCS gene locus has evolved by duplication mechanisms. Evidence for the occurrence of at least one gene conversion event involving the hCS-1 gene precursor and the hCS-2 gene was found, indicating that the hGH/hCS gene locus has evolved by concerted mechanisms. The structure of the hCS genes is discussed in light of recent studies of CS genes from other mammalian species.