Identification, characterization, and expression of a new prolactin-like molecule in the hamster placenta

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.

Measurement of plasma and tissue relaxin concentrations in the pregnant hamster and fetus using a homologous radioimmunoassay

A homologous hamster relaxin RIA was developed to evaluate plasma and tissue concentrations of relaxin in the latter half of pregnancy in this species. Relaxin protein and mRNA were localized using antibodies developed to synthetic hamster relaxin and gene-specific molecular probes, respectively. Molecular weight and isoelectric point of the synthetic and native hormones were identical by electrophoretic methods, and synthetic hamster relaxin was active in the mouse interpubic ligament bioassay. Synthetic hormone was used as tracer and standard with rabbit antiserum to the synthetic hormone in the RIA. Relaxin was assayed in blood samples recovered from the retro-orbital plexus on Days 6, 8, 10, 12, 14, 15, and 16 of gestation and on Days 1 and 5 postpartum. Relaxin was first detected on Day 8 of gestation (3.7 +/- 0.6 ng/ml), increased to reach a maximum in the evening of Day 15 (826.0 +/- 124.0 ng/ml), and decreased by Day 16 (day of parturition). Relaxin concentrations were assayed in aqueous extracts of implantation sites (Days 6, 8, and 10) and chorioallantoic placentae (Days 12, 14, and 15). Concentrations were low on Day 6 (0.02 +/- 0.001 microg/g tissue), increased to Day 15 (6.96 +/- 0.86 microg/g tissue), and subsequently declined by the evening of Day 15. Relaxin protein and mRNA were localized to primary and secondary giant trophoblast cells in the chorioallantoic placental trophospongium. However, relaxin protein was not localized in ovaries of pregnant animals or oviductal tissues of cycling animals. Significant quantities of relaxin were detected in the serum of fetal hamsters recovered on Day 15.

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.

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.