S.M. Khorshed Alam

The prolactin family: effectors of pregnancy-dependent adaptations

Prolactin (PRL) is a hormone involved in many biological functions. In some species, there is a family of PRL-related genes; such is the case in the mouse and rat. The actions of members of the PRL family can be distinguished based on the involvement of the PRL receptor signaling pathway (classical versus nonclassical). Recent insights into the biology of the PRL family have been derived from mouse mutagenesis studies. There is compelling evidence suggesting that the PRL family contributes to the regulation of pregnancy-dependent adaptations to physiological stressors.

A uterine decidual cell cytokine ensures pregnancy-dependent adaptations to a physiological stressor

In the mouse, decidual cells differentiate from uterine stromal cells in response to steroid hormones and signals arising from the embryo. Decidual cells are crucially involved in creating the intrauterine environment conducive to embryonic development. Among their many functions is the production of cytokines related to prolactin (PRL), including decidual prolactin-related protein (DPRP). DPRP is a heparin-binding cytokine, which is abundantly expressed in uterine decidua. In this investigation, we have isolated the mouse Dprp gene, characterized its structure and evaluated its biological role. Dprp-null mice were made by replacing exons 2 to 6 of the Dprp gene with an in-frame enhanced green fluorescent protein (EGFP) gene and a neomycin (neo) resistance cassette. Heterozygous intercross breeding of the mutant mice yielded the expected mendelian ratio. Pregnant heterozygote females expressed EGFP within decidual tissue in locations identical to endogenous Dprp mRNA and protein expression. Homozygous Dprp-null mutant male and female mice were viable, exhibited normal postnatal growth rates, were fertile and produced normal litter sizes. A prominent phenotype was observed when pregnant Dprp-null mice were exposed to a physiological stressor. DPRP deficiency interfered with pregnancy-dependent adaptations to hypoxia resulting in pregnancy failure. Termination of pregnancy was associated with aberrations in mesometrial decidual cells, mesometrial vascular integrity, and disruptions in chorioallantoic placenta morphogenesis. The observations suggest that DPRP participates in pregnancy-dependent adaptations to a physiological stressor.

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-Iα (PL-Iα), PL-Iβ, 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.

Subfertility Linked to Combined Luteal Insufficiency and Uterine Progesterone Resistance

Early pregnancy loss is common and can be caused by a range of factors. The Brown Norway (BN) rat exhibits reproductive dysfunction characterized by small litter size and pregnancy failure and represents a model for investigating early pregnancy loss. In this study, we investigated the establishment of pregnancy in the BN rat and gained insight into mechanisms causing its subfertility. Early stages of BN uteroplacental organization are unique. The BN primordial placenta is restricted in its development and correlates with limited BN uterine decidual development. BN uterine decidua was shown to be both structurally and functionally distinct and correlated with decreased circulating progesterone (P4) levels. Ovarian anomalies were also apparent in BN rats and included decreased ovulation rates and decreased transcript levels for some steroidogenic enzymes. Attempts to rescue the BN uterine decidual phenotype with steroid hormone therapy were ineffective. BN uteri were shown to exhibit reduced responsiveness to P4 but not to 17beta-estradiol. P4 resistance was associated with decreased transcript levels for the P4 receptor (Pgr), a P4 receptor chaperone (Fkbp4), and P4 receptor coactivators (Ncoa1 and Ncoa2). In summary, the BN rat exhibits luteal insufficiency and uterine P4 resistance, which profoundly affects its ability to reproduce.

Decidual Cells Produce a Heparin-binding Prolactin Family Cytokine with Putative Intrauterine Regulatory Actions

Pregnancy in mice and rats is associated with the production of a large family of hormones/cytokines related to prolactin (PRL). The hormones/cytokines are hypothesized to coordinate maternal and fetal adaptations to pregnancy. In this study, PRL-like protein-J (PLP-J, also known as PRL family 3, subfamily c, member 1 (Prl3c1)) is shown to be a product of the uterine decidua and a regulator of postimplantation intrauterine events. PLP-J-specific antibodies and a series of recombinant PLP-J proteins were generated and used to investigate PLP-J expression and as ligands for investigating biological targets. Decidual PLP-J migrates as a 29-kDa protein and localizes to a band of decidual cells surrounding the trophoblast cell layer on gestation day 8.5. PLP-J ligands specifically bound in situ to the surrounding uterine stromal cells and vasculature within the decidua of gestation day 8.5 implantation sites. We then investigated the in vitro actions of PLP-J on uterine stromal cells and endothelial cells. PLP-J specifically interacted with both cell populations. PLP-J promoted uterine stromal cell proliferation and inhibited endothelial cell proliferation. We determined that PLP-J does not interact with PRL receptors. Instead, PLP-J interacts with heparin-containing molecules, including syndecan-1, which is expressed in gestation day 8.5 pregnant uteri, as well as in uterine stromal cells and endothelial cells. The restricted expression of PLP-J and its specific interactions with uterine stromal cells and endothelial cells suggests that it acts locally and regulates decidual cell development and the endometrial vasculature.

A standardized nomenclature for the mouse and rat prolactin superfamilies

Institute of Maternal-Fetal Biology, University of Kansas Medical Center, Kansas City, Kansas, 66160, USA Department of Physiology, University of Manitoba, R3E 3J7, Winnipeg, Manitoba, Canada Department of Molecular and Cellular Physiology, University of Cincinnati, Cincinnati, Ohio, 45267, USA Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, Illinois, 60208, USA Mouse Genome Informatics Resource and Mouse Genomic Nomenclature Committee, The Jackson Laboratory, Bar Harbor, Maine, 04609, USA Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, Iowa, 50011, USA Department of Cellular Biochemistry, Veterinary Medical Sciences/Animal Resource Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku Tokyo, Japan Rat Genome Database, Medical College of Wisconsin, Milwaukee, Wisconsin, 53226, USA Biochemistry Department, School of Life Sciences, University of Sussex, Brighton, BN1 9QG, UK

Identification of target genes for a prolactin family paralog in mouse decidua

Prolactin family 8, subfamily a, member 2 (PRL8A2; also called decidual prolactin-related protein; dPRP) is a member of the expanded prolactin family. PRL8A2 is expressed in the uterine decidua and contributes to pregnancy-dependent adaptations to hypoxia. The purpose of this study was to identify gene targets for PRL8A2 action within the uteroplacental compartment. Affymetrix DNA microarray analysis was performed for RNA samples from WT and Prl8a2 null tissues. Validation of the DNA microarray was performed using quantitative RT-PCR. Nine genes were confirmed with decreased expression in Prl8a2 null tissues (e.g., Klk7, Rimklb, Arhgef6, Calm4, Sprr2h, Prl4a1, Ccl27, Lipg, and Htra3). These include potential decidual, endothelial and trophoblast cell targets positively regulated by PRL8A2. A significant upregulation of Derl3, Herpud1, Creld2, Hsp90b1, Ddit3 and Hspa5 was identified in Prl8a2 null tissues, reflecting an increased endoplasmic reticulum (ER) stress response. ER stress genes were prominently expressed in the uterine decidua. We propose that PRL8A2 is a mediator of progesterone-dependent modulation of intrauterine responses to physiological stressors.

Prolactin Family of the Guinea Pig, Cavia porcellus

Prolactin (PRL) is a multifunctional hormone with prominent roles in regulating growth and reproduction. The guinea pig (Cavia porcellus) has been extensively used in endocrine and reproduction research. Thus far, the PRL cDNA and protein have not been isolated from the guinea pig. In the present study, we used information derived from the public guinea pig genome database as a tool for identifying guinea pig PRL and PRL-related proteins. Guinea pig PRL exhibits prominent nucleotide and amino acid sequence differences when compared with PRLs of other eutherian mammals. In contrast, guinea pig GH is highly conserved. Expression of PRL and GH in the guinea pig is prominent in the anterior pituitary, similar to known expression patterns of PRL and GH for other species. Two additional guinea pig cDNAs were identified and termed PRL-related proteins (PRLRP1, PRLRP2). They exhibited a more distant relationship to PRL and their expression was restricted to the placenta. Recombinant guinea pig PRL protein was generated and shown to be biologically active in the PRL-responsive Nb2 lymphoma cell bioassay. In contrast, recombinant guinea pig PRLRP1 protein did not exhibit PRL-like bioactivity. In summary, we have developed a new set of research tools for investigating the biology of the PRL family in an important animal model, the guinea pig.