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

Central growth hormone action regulates metabolism during pregnancy

The maternal organism undergoes numerous metabolic adaptations to become prepared for the demands associated with the coming offspring. These metabolic adaptations involve changes induced by several hormones that act at multiple levels, ultimately influencing energy and glucose homeostasis during pregnancy and lactation. Previous studies have shown that central growth hormone (GH) action modulates glucose and energy homeostasis. However, whether central GH action regulates metabolism during pregnancy and lactation is still unknown. In the present study, we generated mice carrying ablation of GH receptor (GHR) in agouti-related protein (AgRP)-expressing neurons, in leptin receptor (LepR)-expressing cells or in the entire brain to investigate the role played by central GH action during pregnancy and lactation. AgRP-specific GHR ablation led to minor metabolic changes during pregnancy and lactation. However, while brain-specific GHR ablation reduced food intake and body adiposity during gestation, LepR GHR knockout (KO) mice exhibited increased leptin responsiveness in the ventromedial nucleus of the hypothalamus during late pregnancy, although their offspring showed reduced growth rate. Additionally, both Brain GHR KO and LepR GHR KO mice had lower glucose tolerance and glucose-stimulated insulin secretion during pregnancy, despite presenting increased insulin sensitivity, compared with control pregnant animals. Our findings revealed that during pregnancy central GH action regulates food intake, fat retention, as well as the sensitivity to insulin and leptin in a cell-specific manner. Together, the results suggest that GH acts in concert with other "gestational hormones" to prepare the maternal organism for the metabolic demands of the offspring.

Hypoxia and Placental Development

Hemochorial placentation is orchestrated through highly regulated temporal and spatial decisions governing the fate of trophoblast stem/progenitor cells. Trophoblast cell acquisition of specializations facilitating invasion and uterine spiral artery remodeling is a labile process, sensitive to the environment, and represents a process that is vulnerable to dysmorphogenesis in pathologic states. Hypoxia is a signal guiding placental development, and molecular mechanisms directing cellular adaptations to low oxygen tension are integral to trophoblast cell differentiation and placentation. Hypoxia can also be used as an experimental tool to investigate regulatory processes controlling hemochorial placentation. These developmental processes are conserved in mouse, rat, and human placentation. Consequently, elements of these developmental events can be modeled and hypotheses tested in trophoblast stem cells and in genetically manipulated rodents. Hypoxia is also a consequence of a failed placenta, yielding pathologies that can adversely affect maternal adjustments to pregnancy, fetal health, and susceptibility to adult disease. The capacity of the placenta for adaptation to environmental challenges highlights the importance of its plasticity in safeguarding a healthy pregnancy. Birth Defects Research 109:1309-1329, 2017.© 2017 Wiley Periodicals, Inc.

Placentophagia in weanling female laboratory rats

Placentophagia is common in parturient mammals and offers physiological and behavioral advantages for mothers. In natural environments, weanlings are often present during the birth of younger siblings, but it is unknown if weanling rats are placentophagic or prefer placenta over other substances. To examine this, primiparous rats were remated during the postpartum estrus and their weanling daughters remained in the natal nest during their mother's next parturition. Continuous observation revealed that 58% of weanlings were placentophagic. To determine if this placentophagia occurs away from parturient mothers, weanling females still living in their natal nest were offered placenta, liver, or cake frosting in a novel chamber. They ingested more placenta and liver than frosting. Thus, many weanling female laboratory rats are placentophagic during the birth of younger siblings but do not selectively prefer placenta when tested outside their natal nest. Consequences of placentophagia by weanling female rats are unknown, but it may promote their alloparenting or later postpartum mothering.

Trophoblasts regulate the placental hematopoietic niche through PDGF-B signaling

The placenta is a hematopoietic organ that supports hematopoietic stem/progenitor cell (HSPC) generation and expansion without promoting differentiation. We identified PDGF-B signaling in trophoblasts as a key component of the unique placental hematopoietic microenvironment that protects HSPCs from premature differentiation. Loss of PDGF-B or its receptor, PDGFRβ, induced definitive erythropoiesis in placental labyrinth vasculature. This was evidenced by accumulation of CFU-Es and actively proliferating definitive erythroblasts that clustered around central macrophages, highly reminiscent of erythropoiesis in the fetal liver. Ectopic erythropoiesis was not due to a requirement of PDGF-B signaling in hematopoietic cells but rather in placental trophoblasts, which upregulated Epo in the absence of PDGF-B signaling. Furthermore, overexpression of hEPO specifically in the trophoblasts in vivo was sufficient to convert the placenta into an erythropoietic organ. These data provide genetic evidence of a signaling pathway that is required to restrict erythroid differentiation to specific anatomical niches during development.

Extrapituitary growth hormone

Pituitary somatotrophs secrete growth hormone (GH) into the bloodstream, to act as a hormone at receptor sites in most, if not all, tissues. These endocrine actions of circulating GH are abolished after pituitary ablation or hypophysectomy, indicating its pituitary source. GH gene expression is, however, not confined to the pituitary gland, as it occurs in neural, immune, reproductive, alimentary, and respiratory tissues and in the integumentary, muscular, skeletal, and cardiovascular systems, in which GH may act locally rather than as an endocrine. These actions are likely to be involved in the proliferation and differentiation of cells and tissues prior to the ontogeny of the pituitary gland. They are also likely to complement the endocrine actions of GH and are likely to maintain them after pituitary senescence and the somatopause. Autocrine or paracrine actions of GH are, however, sometimes mediated through different signaling mechanisms to those mediating its endocrine actions and these may promote oncogenesis. Extrapituitary GH may thus be of physiological and pathophysiological significance.

Benzopyrene and experimental stressors cause compensatory differentiation in placental trophoblast stem cells

Stress causes decreased cell accumulation in early periimplantation embryos and the placental trophoblast stem cells derived from them. Benzopyrene and many other stressors activate stress enzymes that lead to suppressed stem cell accumulation through diminished proliferation and increased apoptosis. Trophoblast stem cells proliferate and a subpopulation of early postimplantation trophoblast cells differentiate to produce the first placental hormones that arise in the implanting conceptus. These hormones mediate antiluteolytic effects that enable the continuation of a successful implantation. The normal determination and differentiation of placental trophoblast stem cells is dependent upon a series of transcription factors. But, these transcription factors can also be modulated by stress through the activity of stress enzymes. This review enumerates and analyzes recent reports on the effects of benzopyrene on placental function in terms of the emerging paradigm that placental differentiation from stem cells can be regulated when insufficient production of stem cells is caused by stress. In addition, we review the other effects caused by benzopyrene throughout placental development.

Spatial and temporal expression of the 23 murine Prolactin/Placental Lactogen-related genes is not associated with their position in the locus

Background

The Prolactin (PRL) hormone gene family shows considerable variation among placental mammals. Whereas there is a single PRL gene in humans that is expressed by the pituitary, there are an additional 22 genes in mice including the placental lactogens (PL) and Prolactin-related proteins (PLPs) whose expression is limited to the placenta. To understand the regulation and potential functions of these genes, we conducted a detailed temporal and spatial expression study in the placenta between embryonic days 7.5 and E18.5 in three genetic strains.

Results

Of the 22 PRL/PL genes examined, only minor differences were observed among strains of mice. We found that not one family member has the same expression pattern as another when both temporal and spatial data were examined. There was also no correlation in expression between genes that were most closely related or between adjacent genes in the PRL/PL locus. Bioinformatic analysis of upstream regulatory regions identified conserved combinations (modules) of putative transcription factor binding sites shared by genes expressed in the same trophoblast subtype, supporting the notion that local regulatory elements, rather than locus control regions, specify subtype-specific expression. Further diversification in expression was also detected as splice variants for several genes.

Conclusion

In the present study, a detailed temporal and spatial placental expression map was generated for all murine PRL/PL family members from E7.5 to E18.5 of gestation in three genetic strains. This detailed analysis uncovered several new markers for some trophoblast cell types that will be useful for future analysis of placental structure in mutant mice with placental phenotypes. More importantly, several main conclusions about regulation of the locus are apparent. First, no two family members have the same expression pattern when both temporal and spatial data are examined. Second, most genes are expressed in multiple trophoblast cell subtypes though none were detected in the chorion, where trophoblast stem cells reside, or in syncytiotrophoblast of the labyrinth layer. Third, bioinformatic comparisons of upstream regulatory regions identified predicted transcription factor binding site modules that are shared by genes expressed in the same trophoblast subtype. Fourth, further diversification of gene products from the PRL/PL locus occurs through alternative splice isoforms for several genes.

Pregnancy and lactation modulate maternal splenic growth and development of the erythroid lineage in the rat and mouse

Maternal physiology changes dramatically during the course of gestation and lactation to meet the needs of the developing fetus and newborn. In the present study, we examined the influence of pregnancy and lactation on growth and erythroid gene expression patterns of the maternal spleen. Holtzman Sprague-Dawley rats and CD-1 mice were killed at various stages of gestation and post partum. We observed pregnancy dependent increases in spleen weight and spleen DNA content in both the rat and mouse. In the rat, spleen size was greatest at the end of pregnancy and regressed post partum. In contrast, mouse spleen size peaked by gestational Day 13 and regressed to its non-pregnant weight before parturition. Pregnancy dependent changes in the size of the spleen were primarily due to an increase in red pulp. Maternal spleen expression of erythroid-associated genes (erythroid Krüppel-like factor, erythroid 5-aminolevulinate synthase-2, β-major globin) was influenced by pregnancy and lactation. A pregnancy dependent increase in erythroid progenitors was also observed. In summary, the demands of pregnancy and lactation cause marked adaptations in the maternal spleen. The maternal spleen increases in size and exhibits an expansion of the erythroid lineage.

Prolactin-like protein-f subfamily of placental hormones/cytokines: responsiveness to maternal hypoxia

The prolactin (PRL) family of hormones/cytokines is involved in the maintenance of pregnancy and adaptations to physiological stressors. In this report, we identify and characterize a new member of the rat PRL family, examine the impact of maternal hypoxia on placental PRL family gene expression, and investigate maternal adaptive responses to hypoxia. Perusal of the PRL gene family locus in the rat genome resulted in the identification of a putative new member of the rat PRL family. The new member is closely related to the previously reported PRL-like protein-F (PLP-F) and has been named PLP-Fbeta and the originally characterized PLP-F, now termed PLP-Falpha. The two proteins exhibit structural similarities but possess distinct cell- and temporal-specific expression profiles. In vivo hypoxia stimulates placental PLP-Falpha and PLP-E mRNA expression in the rat and mouse, respectively. Rcho-1 trophoblast cells can differentiate into trophoblast giant cells, express PLP-Falpha, and exhibit enhanced PLP-Falpha mRNA levels when cultured under low oxygen tension (2%). Exposure to hypobaric hypoxia during latter part of pregnancy did not significantly impact the expression of PLP-Fbeta mRNA. Finally, exposure to hypobaric hypoxia during midpregnancy led to increased maternal red blood cells, hemoglobin concentrations, hematocrit, and increased concentrations of maternal splenic mRNAs for key proteins involved in hemoglobin synthesis, erythroid Krüppel-like factor, erythroid 5-aminolevulinate synthase-2, and beta-major globin. In summary, adaptive responses to maternal hypoxia include activation of placental PLP-Falpha/E gene expression, which may then participate in maternal hematological adjustments required for maintaining maternal and fetal oxygen delivery.

Enhanced recovery from thrombocytopenia and neutropenia in mice constitutively expressing a placental hematopoietic cytokine

Expression of the placental hormone, prolactin-like protein E (PLP-E), a potent cytokine that acts on multiple myeloid lineages, is normally restricted to pregnancy and certain hematopoietic disease states. We hypothesized that the restricted pattern of PLP-E expression is necessary to avoid hyperstimulation of myelopoiesis. To test this idea, we have produced PLP-E transgenic mice and analyzed their steady-state blood cell levels. We find that blood cell levels remain in the normal range, and thus the constitutive expression of a cytokine of pregnancy fails to overcome the tight control of hematopoietic set points for blood cell levels. In contrast, an effect of constitutive PLP-E expression is detected during the recovery from low blood platelet levels (acute thrombocytopenia) and from low granulocyte levels (acute neutropenia) but not from anemia. Mice producing high circulating concentrations of PLP-E recover more rapidly from both thrombocytopenia and neutropenia, as seen both by an earlier increase of progenitor numbers in the bone marrow and the earlier return to normal circulating blood cell levels.

A transgenic analysis of mouse lactate dehydrogenase C promoter activity in the testis

Transcription of the mouse testis-specific lactate dehydrogenase c (mldhc) gene is limited to cells of the germinal epithelium. Cloning and analysis of the mldhc promoter revealed that a 100-bp core promoter was able to regulate testis-specific transcription in vitro and in transgenic mice. Surprisingly, expression of the reporter in transgenic testes was limited to pachytene spermatocytes, whereas native LDH-C(4) was detected in pachytene and all later germ cells. To locate additional regulatory sequence that could recapitulate the native LDH-C(4) distribution pattern, we investigated the contribution of 5' and 3' flanking sequences to the regulation of LDH-C(4) expression. We found that transcription factor YY1 binds to the mldhc promoter, that the mldhc 3' untranslated sequence does not permit a postmeiotic expression of a beta-galactosidase reporter in transgenic mice, and that native mldhc mRNA is predominately meiotic, with only a low level of postmeiotic distribution. Our results suggest that the high level of LDH-C(4) in postmeiotic cells results from mRNA and protein stability.

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.

Effect of iron deficiency on placental cytokine expression and fetal growth in the pregnant rat

Iron deficiency anemia is the most common nutritional disorder in the world. Anemia is especially serious during pregnancy, with deleterious consequences for both the mother and her developing fetus. We have developed a model to investigate the mechanisms whereby fetal growth and development are affected by maternal anemia. Weanling rats were fed a control or iron-deficient diet before and throughout pregnancy and were killed at Day 21. Dams on the deficient diet had lower hematocrits, serum iron concentrations, and liver iron levels. Similar results were recorded in the fetus, except that the degree of deficiency was markedly less, indicating compensation by the placenta. No effect was observed on maternal weight or the number and viability of fetuses. The fetuses from iron-deficient dams, however, were smaller than controls, with higher placental:fetal ratios and relatively smaller livers. Iron deficiency increased levels of tumor necrosis factor alpha (TNFalpha) only in the trophoblast giant cells of the placenta. In contrast, levels of type 1 TNFalpha receptor increased significantly in giant cells, labyrinth, cytotrophoblast, and fetal vessels. Leptin levels increased significantly in labyrinth and marginally (P = 0.054) in trophoblast giant cells. No change was observed in leptin receptor levels in any region of the placentas from iron-deficient dams. The data show that iron deficiency not only has direct effects on iron levels and metabolism but also on other regulators of growth and development, such as placental cytokines, and that these changes may, in part at least, explain the deleterious consequences of maternal iron deficiency during pregnancy.

Trophoblast giant-cell differentiation involves changes in cytoskeleton and cell motility

Trophoblast giant-cell differentiation is well-characterized at the molecular level, yet very little is known about how molecular changes affect the cellular functions of trophoblast in embryo implantation. We have found, using both explanted E7.5 mouse embryo ectoplacental cone and the rat choriocarcinoma (Rcho-1) cell line, that trophoblast differentiation is distinguished by dramatic changes in cytoarchitecture and cell behavior. Undifferentiated trophoblast cells contain little organized actin and few small, peripheral focal complexes and exhibit high membrane protrusive activity, while differentiated trophoblast giant cells contain prominent stress fibers, large internal as well as peripheral focal adhesions, and become immotile. The dramatic changes in cell behavior and cytoskeletal organization of giant cells correlate with changes in the activities of the Rho family of small GTPases and a decrease in tyrosine phosphorylation of focal adhesion kinase. Together, these data provide detailed insight into the cellular properties of trophoblast giant cells and suggest that giant-cell differentiation is characterized by a transition from a motile to a specialized epithelial phenotype. Furthermore, our data support a phagocytic erosion, rather than a migratory infiltration, mechanism for trophoblast giant-cell invasion of the uterine stroma.

Murine prolactin-like protein E synergizes with human thrombopoietin to stimulate expansion of human megakaryocytes and their precursors

The aim of this study was to determine the effect of promegakaryocytopoietic murine hormone prolactin-like protein E (PLP-E) on human megakaryocytopoiesis. Human bone marrow CD34+ cells, cultured in serum-free medium with combinations of thrombopoietin (TPO), stem cell factor (SCF), Flt-3 ligand (Flt-3L), and PLP-E, were analyzed via microscopy, flow cytometry, and clonogenic assay. Unlike the situation with mouse cells, PLP-E alone did not promote human megakaryocyte (MK) differentiation, but instead synergizes with TPO to increase colony-forming unit megakaryocyte (CFU-MK), burst-forming unit erythroid (BFU-E), and and colony-forming unit granulocyte erythroid macrophage mixed (CFU-GEMM) expansion, as well as total MK production. These effects can be attributed to an increase in colony frequency, combined with a significantly greater total cell expansion induced by adding PLP-E along with TPO. The number of cells in each CFU-MK colony is an indication of the maturity of the progenitor population, with larger colonies deriving from a more immature progenitor cell. PLP-E significantly expanded immature, intermediate, and mature CFU-MK subsets at 3 days of culture, as well as the intermediate and mature subsets at day 6. PLP-E combined with TPO induced significant expansion of all CFU-MK subsets at all time points. PLP-E further increased the effect of SCF and Flt-3L on TPO-induced total cell and CFU-MK expansion.PLP-E may act as a survival factor for primitive human megakaryocytic and erythroid progenitors. It appears to preserve the highly proliferative immature fraction of the progenitor compartment but by itself does not promote total cell proliferation or human MK production. PLP-E may prove useful in combination with TPO and other cytokines for ex vivo expansion of hematopoietic progenitors to be used in a clinical setting.

Identification and characterization of a new member of the placental prolactin-like protein-C (PLP-C) subfamily, PLP-Cbeta

We have isolated a complementary DNA (cDNA) clone that encodes a new member of the PRL-like protein-C (PLP-C) subfamily of the PRL gene family. The clone was amplified from a 13.5-day-old mouse conceptus cDNA library by PCR using primers based on conserved regions of PLP-C sequences. The full-length cDNA encodes a predicted protein of 241 residues, which contains a putative signal sequence and 2 putative N-linked glycosylation sites. The predicted protein shares 55-66% amino acid identity with mouse PLP-Calpha and rat PLP-D, PLP-H, PLP-Cv, and PLP-C and also contains 6 homologously positioned cysteine residues. Thus, we named this protein PLP-Cbeta for consistency. We have also isolated rat PLP-Cbeta from rat placenta cDNA library. Surprisingly, two messenger RNA (mRNA) isoforms of rat PLP-Cbeta were isolated: one mRNA (rPLP-Cbeta) encodes a 241-amino acid product, but another mRNA (rPLP-Cbetadelta39) lacks 39 bases that encode for a region rich in aromatic amino acids. The 39-bp region corresponds to exon 3 of other PLP-C subfamily members, such as PLP-Calpha, PLP-Cv, and d/tPRP. It suggests that the two isoforms are probably generated by an alternative splicing from a single gene. RT-PCR analysis revealed that the rPLP-Cbeta form was dominantly expressed in placenta, although both isoforms are coexpressed during placentation. The mouse PLP-Cbeta mRNA expression, which was specific to the placenta, was first detected by Northern analysis on embryonic day 11.5 (E 11.5) and persisted until birth. However, in situ hybridization analysis revealed mPLP-Cbeta expression on E 10.5 in specific trophoblast subsets, such as giant cells and spongiotrophoblast cells. mPLP-Cbeta mRNA was detected in the labyrinthine zone on E 18.5, suggesting that spongiotrophoblast cells had penetrated the labyrinthotrophoblast zone. Consistent with the observed expression in trophoblast giant cells, PLP-Cbeta expression was also detected in in vitro differentiated Rcho-1 cells, which express the trophoblast giant cell phenotype. In summary, overall high amino acid identity (79%), the locations of cysteine residues, and consensus sites for N-linked glycosylation between mouse and rat PLP-Cbeta clearly indicate that PLP-Cbeta is a bona fide member of the PLP-C subfamily. The conservation between mouse and rat, the presence of alternative isoforms, and the pattern of expression during gestation suggest the biological significance of PLP-Cbeta during pregnancy.

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.

The human growth hormone gene cluster locus control region supports position-independent pituitary- and placenta-specific expression in the transgenic mouse

The human growth hormone (hGH) cluster contains five genes. The hGH-N gene is predominantly expressed in pituitary somatotropes, whereas the remaining four genes, the chorionic somatomammotropin genes (hCS-L, hCS-A, and hCS-B) and hGH-V, are expressed selectively in the placenta. In contrast, the mouse genome contains a single pituitary-specific GH gene and lacks any GH-related CS genes. Activation of the hGH transgene in the mouse is dependent on its linkage to a previously described locus control region (LCR) located -15 to -32 kilobases upstream of the hGH cluster. The sporadic, nonreproducible expression of hCS transgenes lacking the LCR suggests that they may be dependent on hGH LCR activity as well. To determine whether the hCS genes could be expressed with appropriate placental specificity, a series of five transgenic mouse lines carrying an 87-kilobase human genomic insert encompassing the majority of the hGH gene cluster and the entire contiguous LCR was established. All of the hGH cluster genes were appropriately expressed in each of these lines. High level expression of hGH was restricted to the pituitary and hCS to the labyrinthine layer of the placenta. The expression of the GH cluster genes in their respective tissues paralleled transgene copy numbers irrespective of the transgene insertion site in the host mouse genome. These studies have extended the utility of the transgenic mouse model for the analysis of the full spectrum of hGH gene cluster activation. Further, they support a role for the hGH LCR in placental hCS, as well as pituitary hGH gene activation, and expression.

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.

Identification of four new members of the rat prolactin/growth hormone gene family

The rodent prolactin (PRL)/growth hormone (GH) gene family currently consists of at least 14 distinct genes that are expressed mainly in pituitary, uterus, and/or placenta. We report here the identification of novel four members from rat with significant homology to PRL. The encoding proteins are not homologs of other known members of this hormone family. The four new cDNAs were assigned to PRL family based on sequence homology and were referred to as PRL-like protein-I (PLP-I), PLP-J, PLP-K, and PLP-L, following the current naming order of rodent PLP family, where PLP-H is the most recent gene. They encode amino acids with 211-228 amino acids, and 34-38% identity with PRL. All have one or two N-linked glycosylation sites. Among the examined rat tissues by Northern blot analysis, only PLP-I was expressed in testis. Our results indicate that the rodent PRL/GH gene family is large with at least 18 distinct genes.

Induction of megakaryocyte differentiation by a novel pregnancy-specific hormone

Maturation of megakaryocytes and subsequent platelet release are normally regulated by a network of cytokines, including thrombopoietin and various interleukins. Because abnormal platelet production and activation have been implicated in gestational pathologies, additional pregnancy-specific cytokines may play important roles in the regulation of megakaryocytopoiesis. Consistent with this hypothesis, we have found that the hormone prolactin-like protein E, a placental hormone that we have recently characterized, targets megakaryocytes through a specific cell surface receptor and induces megakaryocyte differentiation through a gp130-dependent signal transduction pathway.

A new member of the mouse prolactin (PRL)-like protein-C subfamily, PRL-like protein-C alpha: structure and expression

In this study, we establish the presence of a unique member of the PRL-like protein-C (PLP-C) subfamily in the mouse, PLP-C alpha, characterize its complementary DNA and gene, and map its chromosomal location and pattern of expression during pregnancy. Mouse PLP-C alpha encodes for a 239 amino acid protein and possesses from 69-71% identity with rat PLP-C, PLP-Cv, PLP-D, and PLP-H. Another feature characteristic of PLP-C subfamily members that is also present in mouse PLP-C alpha is a 6-exon/5-intron gene structure including an aromatic domain encoded by exon 3. Southern analysis with mouse and rat PLP-C subfamily probes suggested the existence of a single mouse PLP-C alpha gene. Mouse PLP-C alpha maps to chromosome 13 along with other members of the mouse PRL family. Expression of mouse PLP-C alpha increases dramatically as gestation advances and is restricted to spongiotrophoblast and trophoblast giant cells of the junctional zone. In summary, we have established the presence of a new PLP-C subfamily member in the mouse and demonstrated its similarity in structure and expression to rat PLP-C subfamily members. This level of conservation between species expands the biological significance of the PLP-C subfamily and provides additional opportunities for genetically evaluating its function.

Identification of trophoblast-specific regulatory elements in the mouse placental lactogen II gene

Placental lactogen II, the major ligand for the PRL receptor during the second half of gestation in rodents, is synthesized specifically by placental trophoblast giant cells. A transient transgenic analysis has been used to localize the giant cell-specific regulatory region within the mouse placental lactogen II gene to sequences between -1340 and -2019 upstream of the transcriptional start site. More precise mapping of the regulatory elements has been accomplished by transfection of promoter constructs into Rcho-1 trophoblast cells, resulting in the characterization of two positive regulatory elements in the -1471 to -1340 region; two other regulatory elements have been implicated but not further characterized, a negative regulatory element between -2019 and -1778 and another positive element within the region from -1340 to -569. Both of the characterized positive regulatory elements are recognized by factors that are enriched in differentiated giant cells compared with proliferative trophoblasts, and these factors are either absent or at low levels in fibroblasts. The complexes that form on the two elements are distinct and neither element competes with the other for factor binding, thus implicating at least two different regulatory elements in late-gestational trophoblast giant cell-specific gene expression.

Three new members of the mouse prolactin/growth hormone family are homologous to proteins expressed in the rat

A search of a mouse expressed sequence tag database for novel messenger RNAs (mRNAs) in the PRL/GH family has identified three clones that are homologous to the rat PRL-like protein A (PLP-A), PRL-like protein B (PLP-B), and decidual/trophoblast PRL-related protein (d/tPRP). Full-length complementary DNA clones for each of these three mouse mRNAs have been sequenced. Mouse PLP-A is predicted to be synthesized as a precursor of 227 residues and secreted as a glycoprotein of 196 amino acids; the secreted protein shares 78% identity with rat PLP-A. The open reading frame for mouse PLP-B encodes a protein of 230 residues; the putative mature glycoprotein of 201 amino acids is 66% identical to rat PLP-B. The third mouse complementary DNA clone encodes a precursor protein of 240 residues and a secreted glycoprotein of 211 amino acids with 64% identity to rat d/tPRP. All three mouse mRNAs are expressed specifically in the placenta or decidua. The highest levels of the PLP-A mRNA are detected on day 12, at which time expression is localized to a subset of trophoblast giant cells, especially those cells that line maternal blood sinuses. PLP-B mRNA levels are high on day 10 in decidual cells and on day 12 in spongiotrophoblasts. The mRNA similar to rat d/tPRP is present at high levels even earlier in gestation (day 8) and is localized to the decidual layer. The identification of PRL-related mRNAs in common between the mouse and rat indicates that the encoded hormones are evolutionarily conserved and, therefore, likely to play important roles in reproductive physiology.