Kyle E. Orwig

Identification and Characterization of a Mouse Homolog for Decidual/Trophoblast Prolactin-Related Protein

Decidual/trophoblast PRL-related protein (d/tPRP) is one member of a large placental PRL gene family composed of at least nine members in the rat and four in the mouse. Only placental lactogen I and II have been characterized in both rat and mouse. The identification of mouse homologs for rat placental PRL family members will facilitate gene manipulation studies aimed at identifying functions for these hormones. In this report, we establish the presence of d/tPRP in the mouse and characterize its complementary DNA, protein, and pattern of expression during mouse gestation. Evaluation of the National Center for Biotechnology Information database of expressed sequence tags resulted in the identification of several mouse complementary DNA clones exhibiting significant homology to rat d/tPRP. One of these clones was obtained from IMAGE Consortium and Research Genetics for further investigation. The full-length mouse clone was found to have an 81% nucleotide homology with rat d/tPRP and to encode a 239-amino acid protein. Like rat d/tPRP, the mouse protein contains two putative N-linked glycosylation sites and six homologously located cysteine residues. Mouse d/tPRP maps to chromosome 13 along with other members of the mouse PRL family. Like the rat, mouse d/tPRP messenger RNA and protein are expressed by antimesometrial decidual cells and spongiotrophoblast and trophoblast giant cells in the junctional zone of the placenta. In summary, we have established the presence of d/tPRP in the mouse and demonstrated its similarity in structure and pattern of expression to rat d/tPRP. This level of conservation between species expands the biological significance of d/tPRP during pregnancy and provides additional opportunities for evaluating its function.

Transcriptional activation of the decidual/trophoblast prolactin-related protein gene.

The decidual/trophoblast PRL-related protein (d/tPRP) is dually expressed by decidual and trophoblast cells during pregnancy. We have characterized the proximal d/tPRP promoter responsible for directing d/tPRP expression in decidual and trophoblast cells. We have demonstrated that the proximal 93 bp of d/tPRP 5′-flanking DNA are sufficient to direct luciferase gene expression in primary decidual and Rcho-1 trophoblast cells, but not in fibroblast, undifferentiated uterine stromal cells or trophoblast cells of a labyrinthine lineage. The 93-bp d/tPRP promoter was also sufficient to direct differentiation-dependent expression in trophoblast giant cells. Mutational analysis demonstrated the differential importance of activating protein-1 and Ets regulatory elements (located within the proximal 93 bp of d/tPRP 5′-flanking DNA) for activation of the d/tPRP promoter in decidual vs. trophoblast cells. Disruption of the activating protein-1 regulatory element inhibited d/tPRP promoter activity by more than 95% in...

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.

Decidual signals in the establishment of pregnancy: The prolactin family

Summary Decidual cells are responsible for creating a uterine environment supportive of the development of extraembryonic and embryonic tissues. A hormone family structurally related to pituitary PRL is a component of the efferent decidual cell response. Thus far, members of the PRL gene family have been identified in primates and in the rat. Patterns of expression during gestation suggest a role for members of the decidual PRL family in the establishment and maintenance of the gestational state. Precise physiological roles for each member of the decidual PRL family remain to be elucidated.

The Rodent Placental Prolactin Family and Pregnancy

Endocrine signals produced by the placenta have a pivotal role in the establishment and maintenance of pregnancy. These signals include hormones, cytokines, and growth factors that act to coordinate events in maternal, extraembryonic, and embryonic compartments. Among the various regulatory signals secreted by the placenta are a prominent family of proteins related to pituitary prolactin (PRL). These proteins have amassed a rich history of investigation in several species.

Trophoblast-specific regulation of endocrine-related genes

Summary In order to increase our understanding of trophoblast-specific transcriptional controls we need to address two important concerns. First, we need to extend the number of genes investigated and the depth of the investigation on each gene. Next, we need to expand the model systems available for studying trophoblast-specific transcriptional controls. Human choriocarcinoma cell lines have been the most commonly used in vitro models. These cell populations have been valuable but are clearly limited in their applicability to all trophoblast cell lineages, especially those from nonprimate species. The Rcho-1 trophoblast cell line has proven to be a valuable model for the rodent trophoblast giant cell lineage (Soares et al., 1996). The further implementation of primary trophoblast culture models is paramount, as is the refinement of in vivo strategies for studying trophoblast-specific gene regulation.