Relaxin in the marmoset monkey: secretion pattern in the ovarian cycle and early pregnancy

Chemical cues of female fertility states in a non-human primate

An increasing number of studies suggest that olfaction is important for communication throughout the order of primates. Callitrichids, in particular, have well-developed olfactory systems and use anogenital glands to produce scent marks. Behavioural studies have shown that male common marmosets (Callithrix jacchus) distinguish between odours from the peri-ovulatory and luteal phase of females. However, large gaps remain in understanding the chemical underpinnings of olfactory cues. To investigate whether chemical cues vary with female fertility and reproductive quality, our study combined behavioural bioassays with chemical analyses of the anogenital odours of female common marmosets using gas chromatography-mass spectrometry. We found that cycle states, age and parity have an impact on chemical profiles and further identified affected chemical substances. Our results confirm and expand on previous behavioural evidence for cues of fertility. Our results indicate that cycle-related substances likely act as chemical cues. Males could use such olfactory fertility cues to optimize their mating effort and thereby increase their paternity certainty. This certainty could enhance paternal care for their infants. The results of our study open a promising avenue to find the metabolic pathways from which chemical cues of fertility arise and to unravel their importance during primate evolution in future comparative studies.

Immune-endocrine crosstalk during pregnancy

The success of pregnancy depends mostly on a synchronized immune-endocrine crosstalk at the maternal-fetal interface. Hormones are important in terms of maintaining the suitable environment and sufficient nutrition for the developing fetus. They also play a major role during the process of parturition and lactation. Maternal immunomodulation is important for the tolerance of semiallogeneic fetus. This is achieved in concert with a variety of endocrine stimulation. Estrogen, progesterone, and Human Chorionic Gonadotropin play a major role in immune modulation during pregnancy. Hormones modulate B cells, dendritic cells, uterine natural killer cells, macrophages, neutrophils to adopt fetal friendly immune phenotypes. Recently the use of hormones in assisted reproductive technology has been found to improve the pregnancy outcome. The present review focuses on the pregnancy-related hormones, their role in immunomodulation for successful pregnancy outcome. This also shed light on the immune-endocrine crosstalk at maternal-fetal interface during pregnancy.

Evolution of the relaxin/insulin-like gene family in anthropoid primates

The relaxin/insulin-like gene family includes signaling molecules that perform a variety of physiological roles mostly related to reproduction and neuroendocrine regulation. Several previous studies have focused on the evolutionary history of relaxin genes in anthropoid primates, with particular attention on resolving the duplication history of RLN1 and RLN2 genes, which are found as duplicates only in apes. These studies have revealed that the RLN1 and RLN2 paralogs in apes have a more complex history than their phyletic distribution would suggest. In this regard, alternative scenarios have been proposed to explain the timing of duplication, and the history of gene gain and loss along the organismal tree. In this article, we revisit the question and specifically reconstruct phylogenies based on coding and noncoding sequence in anthropoid primates to readdress the timing of the duplication event giving rise to RLN1 and RLN2 in apes. Results from our phylogenetic analyses based on noncoding sequence revealed that the duplication event that gave rise to the RLN1 and RLN2 occurred in the last common ancestor of catarrhine primates, between ∼44.2 and 29.6 Ma, and not in the last common ancestor of apes or anthropoids, as previously suggested. Comparative analyses based on coding and noncoding sequence suggests an event of convergent evolution at the sequence level between co-ortholog genes, the single-copy RLN gene found in New World monkeys and the RLN1 gene of apes, where changes in a fraction of the convergent sites appear to be driven by positive selection.

Relaxin: a hormonal aid to diagnose pregnancy status in wild mammalian species

In the beginning of 1960s, seminal studies characterizing circulating concentrations of immunoreactive relaxin in companion dogs and evaluating the differences in concentrations among pregnant, nonpregnant, and pseudopregnant bitches indicated the potential for relaxin to be applied clinically as a diagnostic aid to detect pregnancy status in wild animal species. A brief historical overview of the nature of relaxin and early work to develop and validate immunologic methods to analyze relaxin in the blood of rodents and pigs is initially discussed, which is followed by a summary of the development and validation of relaxin immunoassays to diagnose pregnancy in companion dogs and cats. Thereafter, observation of the pregnancy-specific increase in circulating concentrations of relaxin in laboratory, companion, and farm animal species leads to discussion on the application of radioimmunoassays, enzyme immunoassays, and a rapid immunomigration assay to diagnose pregnancy in wild terrestrial (e.g., wolves, lions, elephants, rhinoceros, panda) and marine (e.g., seals, dolphins) mammal species. A reference table is included with a comprehensive list of numerous species and essential reagents that have been used in various in-house and commercial immunoassays to successfully analyze relaxin quantitatively and qualitatively in blood (serum or plasma) and to some extent in urine. Although the detection of relaxin concentrations has the potential to aid in the diagnosis of pregnancy in many wild animal species, there are challenges in other species. Future efforts should focus on validation of nonradiolabeled relaxin immunoassays for broader application among species and improving techniques (e.g., extraction, purification) to analyze relaxin in samples other than blood (e.g., urine, feces, saliva, blow, skin, blubber) that can be collected in a less-invasive or -stressful manner and processed accordingly for basic and applied purposes, especially with application toward conservation of threatened or endangered species.

Relaxins enhance growth of spontaneous murine breast cancers as well as metastatic colonization of the brain

Relaxins are known for their tissue remodeling capacity which is also a hallmark of cancer progression. However, their role in the latter context is still unclear, particularly in breast cancer. In a mouse model with spontaneously arising breast cancer due to erbB2-overexpression we show that exposure to porcine relaxin results in significantly enhanced tumour growth as compared to control animals. This is accompanied by increased serum concentrations of progesterone and estradiol as well as elevated expression of the respective receptors and the relaxin receptor RXFP1 in the tumour tissue. It is also associated with enhanced infiltration by tumour-associated macrophages which are known to promote tumour progression. Additionally, we show in an ex vivo model of metastatic brain colonization that porcine relaxin as well as human brain-specific relaxin-3 promotes invasion into the brain tissue and enhance interaction of breast cancer cells with the resident brain macrophages, the microglia. Relaxin signaling is mediated via RXFP1, since R 3/I5, a specific agonist of the relaxin-3 receptor RXFP3 in the brain, does not significantly enhance invasion. Taken together, these findings strongly support a role of relaxins in the progression of breast cancer where they foster primary tumour growth as well as metastatic colonization by direct and indirect means.

Relaxin family peptides and their receptors

There are seven relaxin family peptides that are all structurally related to insulin. Relaxin has many roles in female and male reproduction, as a neuropeptide in the central nervous system, as a vasodilator and cardiac stimulant in the cardiovascular system, and as an antifibrotic agent. Insulin-like peptide-3 (INSL3) has clearly defined specialist roles in male and female reproduction, relaxin-3 is primarily a neuropeptide involved in stress and metabolic control, and INSL5 is widely distributed particularly in the gastrointestinal tract. Although they are structurally related to insulin, the relaxin family peptides produce their physiological effects by activating a group of four G protein-coupled receptors (GPCRs), relaxin family peptide receptors 1-4 (RXFP1-4). Relaxin and INSL3 are the cognate ligands for RXFP1 and RXFP2, respectively, that are leucine-rich repeat containing GPCRs. RXFP1 activates a wide spectrum of signaling pathways to generate second messengers that include cAMP and nitric oxide, whereas RXFP2 activates a subset of these pathways. Relaxin-3 and INSL5 are the cognate ligands for RXFP3 and RXFP4 that are closely related to small peptide receptors that when activated inhibit cAMP production and activate MAP kinases. Although there are still many unanswered questions regarding the mode of action of relaxin family peptides, it is clear that they have important physiological roles that could be exploited for therapeutic benefit.

Constitutive formation of an RXFP1-signalosome: a novel paradigm in GPCR function and regulation

The classical second messenger cAMP is important in diverse physiological processes, where its spatial and temporal compartmentalization allows precise control over multiple cellular events. Within this context, G-protein-coupled receptors (GPCRs) govern specialized pools of cAMP, which are functionally specific for the unique cellular effects attributed to a particular system. The relaxin receptor, RXFP1, is a GPCR that exerts pleiotropic physiological effects including a potent anti-fibrotic response, increased cancer metastases, and has efficacy as a vasodilator in heart failure. On a cellular level, relaxin stimulation of RXFP1 results in the activation of multiple G-protein pathways affecting cAMP accumulation. Specificity and diversity in the cAMP signal generated by RXFP1 is controlled by differential G-protein coupling dependent upon the background of cellular expression, and cAMP compartmentalization. Further complexity in cAMP signalling results from the constitutive assembly of an RXFP1-signalosome, which specifically responds to low concentrations of relaxin, and activates a distinct cAMP pathway. The RXFP1-signalosome is a higher-order protein complex that facilitates receptor sensitivity to attomolar concentration of peptide, exhibits constitutive activity and dual coupling to G-proteins and β-arrestins and reveals a concentration-biased agonism mediated by relaxin. The specific and directed formation of GPCR-centered signalosomes allows an even greater spatial and temporal control of cAMP, thus rationalizing the considerable physiological scope of this ubiquitous second messenger.

The molecular detection of relaxin and its receptor RXFP1 in reproductive tissue of Felis catus and Lynx pardinus during pregnancy

Relaxin acts as a pregnancy-specific signal in feline species, but specific information about protein structure and binding is essential for the improvement of pregnancy diagnosis in endangered feline species, like the Iberian lynx. To generate a felid-specific relaxin antibody, the DNA and protein sequences of lynx and cat were determined and peptides were chosen for antibody generation. In addition, relaxin and relaxin receptor (RXFP1) mRNA expressions were measured in uteri and ovaries of pregnant domestic cats and lynx placentae. Using real-time PCR and immunohistochemistry, it was established that feline placenta is the main source of relaxin during pregnancy. In other tested tissues, relaxin mRNA expression was weak. TheRXFP1mRNA expression was found mainly in cat uterine tissue and feline placentae. It was assumed that these tissues were main targets for relaxin. In the ovary, relaxin immunostaining was associated with blood vessels, signifying its role in vascularization.

Examination of relaxin and its receptors expression in pig gametes and embryos

BACKGROUND

Relaxin is a small peptide also known as pregnancy hormone in many mammals. It is synthesized by both male and female tissues, and its secretions are found in various body fluids such as plasma serum, ovarian follicular fluid, utero-oviduct secretions, and seminal plasma of many mammals, including pigs. However, the presence and effects of relaxin in porcine gametes and embryos are still not well-known. The purpose of this study was to assess the presence of relaxin and its receptors RXFP1 and RXFP2 in pig gametes and embryos.

METHODS

Immature cumulus-oocyte complexes (COCs) were aspirated from sows' ovaries collected at the abattoir. After in vitro-maturation, COCs were in vitro-fertilized and cultured. For studies, immature and mature COCs were separately collected, and oocytes were freed from their surrounding cumulus cells. Denuded oocytes, cumulus cells, mature boar spermatozoa, zygotes, and embryos (cleaved and blastocysts) were harvested for temporal and spatial gene expression studies. Sections of ovary, granulosa and neonatal porcine uterine cells were also collected to use as controls.

RESULTS

Using both semi-quantitative and quantitative PCRs, relaxin transcripts were not detected in all tested samples, while RXFP1 and RXFP2 mRNA were present. Both receptor gene products were found at higher levels in oocytes compared to cumulus cells, irrespective of the maturation time. Cleaved-embryos contained higher levels of RXFP2 mRNA, whereas, blastocysts were characterized by a higher RXFP1 mRNA content. Using western-immunoblotting or in situ immunofluorescence, relaxin and its receptor proteins were detected in all samples. Their fluorescence intensities were consistently more important in mature oocytes than immature ones. The RXFP1 and RXFP2 signal intensities were mostly located in the plasma membrane region, while the relaxin ones appeared homogeneously distributed within the oocytes and embryonic cells. Furthermore, spermatozoa displayed stronger RXFP2 signal than RXFP1 after western-immunoblotting.

CONCLUSION

All together, our findings suggest potential roles of relaxin and its receptors during oocyte maturation, early embryo development, and beyond.

Luteotrophic effects of relaxin, chorionic gonadotrophin and FSH in common marmoset monkeys (Callithrix jacchus)

In early pregnant primates, relaxin (RLX) is highly upregulated within the corpus luteum (CL), suggesting that RLX may have an important role in the implantation of the blastocyst. Therefore, the aim of the present study was to investigate the local effects of RLX and gonadotrophins on the maintenance of the CL using an in vitro microdialysis system. CLs of common marmoset monkeys were collected by luteectomy during different stages of the luteal phase and early pregnancy. Each CL was perfused with either Ringer's solution alone or Ringer's solution supplemented with either porcine RLX (250, 500 and 1000 ng/ml) or gonadotrophins (50 IU/ml). Application of RLX provoked a significant luteal response of progesterone (P(4)) and oestradiol (E(2)) secretions during the mid-luteal phase (500 ng/ml: P(4) 54+/-42%, E(2) 24+/-11%; 1000 ng/ml: E(2) 16+/-13%), and especially during the late luteal phase (250 ng/ml: P(4) 53+/-10%; 500 ng/ml: P(4) 44+/-15%; 1000 ng/ml: P(4) 62+/-15%, E(2) 18+/-7%). The effects of RLX on steroid secretion were irrespective of the RLX dosages. While treatment with human chorionic gonadotrophin did not affect luteal steroid or RLX secretion, the application of FSH resulted in a significant increase in the secretion of both P(4) (20+/-8%) and E(2) (37+/-28%), and a prominent rise in RLX during early pregnancy. In conclusion, our results demonstrate that RLX and FSH have a luteotrophic function in the marmoset monkeys; moreover, FSH has a function beyond its traditional role just as a follicle-stimulating hormone.

Validation of a homologous canine relaxin radioimmunoassay and application with pregnant and non-pregnant Northern fur seals (Callorhinus ursinus)

The primary objectives of this study were to validate a canine relaxin RIA for use in otariids and phocids and consider practical applications. For 6 captive Northern fur seal females, serum samples were grouped and examined according to pregnancy (n=13), post-partum (n=8) and non-pregnancy (n=6), and, for 2 captive Northern fur seal males, serum samples were grouped and examined together regardless of age (2 mo-15 yrs, n=6). Placental tissue was available for examination from one Northern fur seal, Steller sea lion and harbor seal. The validation process involved several steps using an acid-acetone extraction process to isolate a relaxin-containing fraction in pools of serum from each group of fur seals and placental tissue from each seal species. A relaxin-like substance was detected in extracts of pregnant, non-pregnant and male serum and placental tissue in a dose-responsive manner as increasing volumes of respective extracts or amounts of canine relaxin were introduced into the assay. In raw serum samples, mean immuno-reactive relaxin concentrations were higher (P<0.05) during pregnancy than post-partum and non-pregnancy, and lower (P<0.05) in male than female fur seals. During pregnancy, mean serum concentrations of relaxin progressively increased (P<0.05) over Months 4-10 and, in serial samples collected from the same fur seals before and after parturition, mean concentrations were higher (P<0.06) pre-partum than post-partum. In conclusion, validation of a homologous canine relaxin RIA for use in otariids and phocids resulted in the discovery of a relaxin-like substance in extracted and raw serum and placental tissue from Northern fur seals, a Steller sea lion and harbor seal. Distinctly higher immuno-reactive concentrations during pregnancy indicated the potential for relaxin to serve as a hormonal marker to differentiate between pregnant and non-pregnant or pseudopregnant pinnipeds.

Prolonged RXFP1 and RXFP2 signaling can be explained by poor internalization and a lack of beta-arrestin recruitment

Relaxin induces sustained physiological responses, which brings into question the deactivation processes typical of most G protein-coupled receptors (GPCR) for its receptor, relaxin family peptide receptor 1 (RXFP1). Here, we examined relaxin-dependent phosphorylation of RXFP1 and the related insulin-like peptide 3 (INSL3) receptor, RXFP2, as well as the capacity of these receptors to recruit beta-arrestins and internalize in response to ligand stimulation. We confirmed in human embryonic kidney (HEK)-293T cells, expressing RXFP1 or RXFP2, that both receptors elicit prolonged cAMP responses up to 6 h after stimulation. Receptors immunoprecipitated from (32)P metabolically labeled cells were used to investigate the agonist-specific phosphorylation. Rapid and robust receptor phosphorylation was not observed for either RXFP1 or RXFP2, although some (32)P-incorporation was observed at 30 min; however, this was not statistically significant. In accord with this result, RXFP1 and RXFP2 demonstrated poor internalization in response to relaxin or INSL3, as compared with the angiotensin II type 1 receptor (AT(1)R), which undergoes rapid and robust phosphorylation and internalization in response to angiotensin II. Additionally, coexpression of GPCR kinases has no effect on the rate of internalization for either RXFP1 or RXFP2. Confocal microscopy was used to follow the trafficking of green fluorescent protein-labeled beta-arrestins after receptor activation. Neither RXFP1 nor RXFP2 activation results in recruitment of beta-arrestins to the cell surface, whereas AT(1)R rapidly recruits both beta-arrestins-1 and -2. The apparent lack of classical regulation for RXFP1 and RXFP2 provides the molecular basis for the prolonged signaling and physiological actions of relaxin and related peptides.

The hormonal induction of cervical remodeling in the common marmoset monkey (Callithrix jacchus)

Controversy still exists regarding the involvement of relaxin (RLX) in cervical reorganization throughout parturition in the human, despite its well-known role in facilitating extensive extracellular matrix (ECM) remodeling in diverse organs. Therefore, the aim of the present study was to examine the influence of RLX and estrogen (E2) on the cervical tissue of the common marmoset monkey. Two experimental designs were used: 1)in vivoanalysis of the intracervical diameter under locally applied RLX and 2) ovariectomized (ov) marmosets were treated systemically with either recombinant human (rh) RLX, E2 or rhRLX+E2 to examine their action on the cervix.In vivo-locally applied rhRLX induced a distinct and significant widening of the cervix (before: 4.8±1.1 mm versus after: 5.7±0.9 mm in diameter;P<0.030, MV±s.e.m.). This widening effect was most pronounced in animals without previous pregnancies.In vitroinvestigation of cervical tissue showed significantly increased wet weights after all three hormone treatments (E2: 0.27±0.07 g, RLX: 0.25±0.04 g, E2+RLX: 0.30±0.11 g; allP<0.05; MV±s.e.m.) versus controls (0.10±0.04 g). Furthermore, morphological changes such as loosening of the connective tissue structure and decline in collagen content, an increase in the number of eosinophils, increased the expression of matrix metalloproteinases (MMP1) and MMP2, as well as gene and protein expression of the RLX receptor RXFP1 could be detected in the cervical tissue after all hormone treatments, compared with controls. In summary, RLX has a potent widening effect on the cervix of the common marmoset monkey. Although E2 is not required for this RLX effect, a combined application of E2 and RLX induced the most prominent cervical ripening.

Systematic determination of differential gene expression in the primate corpus luteum during the luteal phase of the menstrual cycle

The molecular and cellular processes required for development, function, and regression of the primate corpus luteum (CL) are poorly defined. We hypothesized that there are dynamic changes in gene expression occurring during the CL life span, which represent proteins and pathways critical to its regulation. Therefore, a genomic approach was utilized to systematically identify differentially expressed genes in the rhesus macaque CL during the luteal phase of natural menstrual cycles. CL were collected between d 3-5 (early stage), d 7-8 (mid), d 10-12 (mid-late), d 14-16 (late), or d 18-19 (very-late) after the midcycle LH surge. From the early through very-late stages, 3234 transcripts were differentially expressed, with 879 occurring from the early through late stages that encompass the processes of luteinization, maintenance, and functional regression. To characterize gene changes most relevant to these processes, ontology analysis was performed using the list of 879 differentially expressed transcripts. Four main groups of related genes were identified with relevance to luteal physiology including: 1) immune function; 2) hormone and growth factor signaling; 3) steroidogenesis; and 4) prostaglandin biosynthesis, metabolism, and signaling. A subset of genes representing each of the four major categories was selected for validation of microarray results by quantitative real-time PCR. Results in mRNA levels were similar between the two methodologies for 17 of 18 genes. Additionally, protein levels for three genes were determined by Western blot analysis to parallel mRNA levels. This database will facilitate the identification of many novel or previously underappreciated pathways that regulate the structure and function of the primate CL.

Repeated induction of abortion in bitches and the effect on plasma concentrations of relaxin, progesterone and estradiol-17beta

The aim of the present study was to investigate the effects of two medications on two subsequent abortions and plasma hormone concentrations of dogs. For this purpose, two groups of bitches (n=5 each), received the antiprogesterone aglepristone (Alizine) at 10mg/kg body weight on two subsequent days around day 30 after mating. In group II, the antiprolactin cabergoline (Galastop) was additionally administered po at 5 microg/kg body weight until the start of abortion. The plasma concentrations of relaxin, progesterone (P4) and estradiol-17beta (E2) were measured before, during and after each abortion. During the next cycle after the abortion, the same bitches were mated again and in pregnant animals, induction of abortion was performed as before. During the third cycle, pregnant bitches were allowed to whelp. Termination of first pregnancy occurred significantly earlier after the combined treatment (6.8 versus 10.6 days, p<0.05). In both groups and during both abortions, relaxin varied between individuals; however, there was a continuous decrease after the abortions and no significant differences between groups (p>0.05). In one bitch with high relaxin concentrations before treatment (11.6 ng/ml), a cystic endometrial hyperplasia was diagnosed. In the aglepristone only group, P4 concentrations increased significantly after the first application (p<0.05), then decreased continuously until day 45 after the beginning of abortion. In the combined group, there was a continuous decrease until day 45 (p>0.05). At this time, P4 concentrations between 0.47 and 84.9 nmol/l were measured in both groups. The level of E2 over time was not influenced by any medication. We therefore note that the two medications mainly influenced plasma concentrations of P4 in different ways, probably due to specific treatment-hormone interactions. However, all measurements fell within the range considered normal.

Relaxin and phosphodiesterases collaborate during decidualization

During the evolution of mammals, the endometrium has developed for one reason only: to implant an embryo in the uterus. In higher primates, should an oocyte fail to be fertilized, then the endometrial layer is sloughed off during menses and the menstrual cycle starts again with a new round of endometrial differentiation. This stromal differentiation process is called decidualization and is accompanied in vivo by sustained high levels of intracellular cAMP. The present study was conducted to determine whether manipulation of cAMP-phosphodiesterase (PDE) activities in cultured human endometrial stromal cells could positively influence the decidualization process. The combination of relaxin treatment with inhibition of PDE4 by the specific inhibitor rolipram induced a strong increase in relaxin-mediated cAMP production, both acutely, after 20 min, and after long-term treatment for 3 days, to promote a sustained intracellular cAMP concentration. Moreover, there was a dramatic synergistic effect on the decidualization phenotype, characterized both morphologically and by increased production of prolactin and insulin-like growth factor binding protein-1 gene transcripts. The observations that expression of PDE4D transcripts were selectively increased by cAMP and that inhibition of protein kinase A by H89 to potentially block negative feedback regulation enhanced the relaxin/rolipram-mediated cAMP accumulation lead to a complex picture of cAMP regulation in these cells. There appears to be a coordinated contribution by relaxin and PDE4 at different levels to promote a sustained increased cAMP concentration during decidualization, and thus to provide an adequate maternal interface for the implanting blastocyst.

Elevated Concentrations of Serum Relaxin are Associated with Metastatic Disease in Breast Cancer Patients

Relaxin (RLX) is known to induce remodeling of benign stromal tissues through upregulation of matrix metalloproteases (MMPs). Recently, we could show that RLX also induces MMPs in breast cancer cells and enhances in vitro invasiveness. To investigate its potential role for progression of breast cancer in vivo, RLX serum concentrations were determined in 160 breast cancer patients during post-surgical follow-up. RLX concentrations in cancer patients were significantly higher than in a control population of healthy blood donors and patients with various other diseases (0.47 versus 0.29 ng/ml, p < 0.0001). There was a significant difference between patients with metastases (0.62 ng/ml) and those without (0.38 ng/ml, p < 0.0001). Overall survival was shorter in RLX-positive ( > 0.4 ng/ml) than in RLX-negative patients (p = 0.016). Cox regression analysis showed that RLX was not an independent variable, in contrast to metastatic disease and primary lymph node involvement. Taken together, the detection of elevated RLX concentrations especially in patients with metastases supports the assumption that there is a role for RLX in tissue remodeling during breast cancer progression.

Biology of primate relaxin: a paracrine signal in early pregnancy?

Relaxin is a peptide hormone that exerts numerous effects in a variety of tissues across a broad range of species. Although first identified more than 75 years ago interest in relaxin biology has waxed and waned over the years consistent with peaks and troughs of new experimental data on its wide-ranging biological effects and advances in relaxin enabling technologies. Recent insights into species-dependent differences in relaxin biology during pregnancy have once again stimulated a relative surge of interest in the study of relaxin's reproductive biology. Identification and pharmacological characterization of orphaned relaxin receptors and exploration of its paracrine effects on pregnancy using genomic and proteomic technologies have succeeded in fueling current interest in relaxin research. Primates and non-primate vertebrates exhibit very disparate profiles of relaxin genomics, proteomics and functional biology. Non-human primates appear to exhibit a very close similarity to humans with respect to relaxin reproductive biology but the similarities and subtle differences are only just beginning to be understood. We, and others, have shown that relaxin produces significant changes to the non-human primate endometrium during the peri-implantation period that are consistent with relaxin's long perceived role as a paracrine modulator of pregnancy. The purpose of this review is to summarize the reproductive biology of relaxin in non-human primates with a specific emphasis on the paracrine role of ovarian and endometrial relaxin during embryo implantation and early pregnancy.

Relaxin's physiological roles and other diverse actions

Relaxin has vital physiological roles in pregnant rats, mice, and pigs. Relaxin promotes growth and softening of the cervix, thus facilitating rapid delivery of live young. Relaxin also promotes development of the mammary apparatus, thus enabling normal lactational performance. The actions of relaxin on the mammary apparatus vary among species. Whereas relaxin is required for development of the mammary nipples in rats and mice, it is essential for prepartum development of glandular parenchyma in pregnant pigs. During pregnancy relaxin also inhibits uterine contractility and promotes the osmoregulatory changes of pregnancy in rats. Recent studies with male and nonpregnant female rodents revealed diverse therapeutic actions of relaxin on nonreproductive tissues that have clinical implications. Relaxin has been reported to reduce fibrosis in the kidney, heart, lung, and liver and to promote wound healing. Also, probably through its vasodilatory actions, relaxin protects the heart from ischemia-induced injury. Finally, relaxin counteracts allergic reactions. Knowledge of the diverse physiological and therapeutic actions of relaxin, coupled with the recent identification of relaxin receptors, opens numerous avenues of investigation that will likely sustain a high level of research interest in relaxin for the foreseeable future.

Human embryo implantation: current knowledge and clinical implications in assisted reproductive technology

A pregnancy rate of approximately 15% per cycle renders the process of human reproduction inefficient. The cycle-dependent expression of molecules involved in the embryo-endometrial dialogue has lead to the identification of a 'window of implantation'. This is the unique temporal and spatial expression of factors that allows the embryo to implant (via signalling, appositioning, attachment and invasion) in a specific time frame of 48 h, 7-10 days after ovulation. Integrin molecules, L-selectin ligands, mucin-1, heparin-binding epidermal growth factor and pinopodes are involved in appositioning and attachment. The embryo produces cytokines and growth factors [interleukins, prostaglandins, vascular endothelial growth factor (VEGF)] and receptors for endometrial signals (leukaemia inhibitory factor receptor, colony stimulating factor receptor, insulin-like growth factors and heparin binding epidermal growth factor receptor). The immune system plays an important role. Immunomodulatory factors such as glycodelin, inhibin and interleukin prevent a graft-versus-host reaction. Angiogenesis controlled by VEGF and prostaglandins is needed for formation of a receptive endometrium and a placenta. Identification of these factors has led to their use as markers of implantation that may identify defects causing subfertility. An ideal marker of implantation is sensitive and specific, and easy to obtain without disturbing implantation. Glycodelin and leukaemia inhibitory factor (serum) and integrins and pinopodes (biopsies) are promising candidates.

Immunoexpression of the relaxin receptor LGR7 in breast and uterine tissues of humans and primates

BACKGROUND

The receptor for the peptide hormone relaxin has recently been identified as the heptahelical G-protein coupled receptor, LGR7. In order to generate molecular tools with which to characterize both in vivo and in vitro expression of this receptor in human and primate tissues, specific monotypic antibodies have been generated and applied to a preliminary analysis of human and primate female reproductive tissues.

METHODS

Three peptide sequences were identified from the proposed open reading frame of the cloned LGR7 receptor gene, representing both extracellular and intracellular domains. Two to three rabbits were immunized for each epitope, and the resulting sera subjected to a systematic validation using cultured cells transiently transfected with a receptor-expressing gene construct, or appropriate control constructs.

RESULTS

Human and monkey (marmoset, macaque) endometrium showed consistent and specific immunostaining in the stromal cells close to glands. Staining appeared to be more intense in the luteal phase of the cycle. Weak immunostaining was also evident in the endometrial epithelial cells of the marmoset. A myoma in one patient exhibited strong immunostaining in the circumscribing connective tissue. Uterine expression was supported by RT-PCR results from cultured primary endometrial and myometrial cells. Human breast tissue (healthy and tumors) consistently indicated specific immunostaining in the interstitial connective (stromal) tissue within the glands, but not in epithelial or myoepithelial cells, except in some tumors, where a few epithelial and tumor cells also showed weak epitope expression.

CONCLUSIONS

Using validated monotypic antibodies recognizing different epitopes of the LGR7 receptor, and from different immunized animals, and in different primate species, a consistent pattern of LGR7 expression was observed in the stromal (connective tissue) cells of the endometrium and breast, consistent also with the known physiology of the relaxin hormone.

Characterization of 17beta-hydroxysteroid dehydrogenase type 7 in reproductive tissues of the marmoset monkey

In contrast to the known rodent enzymes, the physiological significance of 17beta-hydroxysteroid dehydrogenase type 7 (17HSD7) and its presumed function in reproductive biology is not well understood in primates. As a first step, we recently cloned the complete coding regions of human and marmoset monkey (Callithrix jacchus) 17HSD7 (cj17HSD7). In the present work the complete cDNA of marmoset 17HSD1 (cj17HSD1), including the proximal promoter region, and a partial sequence of marmoset aromatase (cjARO) were sequenced in order to compare the expression of these estradiol synthesizing enzymes with that of 17HSD7 in a primate model and to identify tissues where 17HSD7 might participate in the pathway of estradiol synthesis. The gene structures of cj17HSD1 and cj17HSD7 were determined and proved to be very similar to the human orthologues. Northern hybridization showed that cjARO mRNA seems to be coexpressed preferably with cj17HSD1 in placenta, whereas in other tissues it is expressed in parallel only with cj17HSD7. Especially in corpora lutea, the cj17HSD7 transcript is detectable throughout the luteal phase of the ovarian cycle and increases during pregnancy, in parallel with the transcript of aromatase. Results were confirmed by immunoblots and immunohistochemistry using new polyclonal antisera directed against cj17HSD7 and cjARO protein. The enzymatic conversion of estrone to estradiol was assessed in marmoset corpora lutea. The pattern of coexpression with aromatase supports the hypothesis that luteal 17HSD7 complements placental 17HSD1, ensuring continued estradiol synthesis throughout pregnancy in primates.

Relaxin peptides are new global players

Relaxin (RLX) has come of age. From being one of the earliest hormones described with a very specific function in parturition, recent research has now shown that it is involved in a variety of roles, from endometrial differentiation during embryo implantation, to being a response factor in infarct and wound situations. It ameliorates fibrosis, and might also be involved in tumour growth and progression. And it is not alone: two other closely related peptide hormones have recently been identified, one specific for the brain, the other with roles in testicular descent and ovarian apoptosis. Finally, the recent cloning of the RLX receptors now provides the basis for a new molecular pharmacology for these peptide hormones, and preliminary studies suggest that their signal transduction is both interesting and unusual.

Chorionic gonadotropin has a recent origin within primates and an evolutionary history of selection

Chorionic gonadotropin (CG) is a critical signal in establishing pregnancy in humans and some other primates, but this placentally expressed hormone has not been found in other mammalian orders. The gene for one of its two subunits (CG beta subunit [CGbeta]) arose by duplication from the luteinizing hormone beta subunit gene (LHbeta), present in all mammals tested. In this study, 14 primate and related mammalian species were examined by Southern blotting and DNA sequencing to determine where in mammalian phylogeny the CGbeta gene originated. Bats (order Chiroptera), flying lemur (order Dermoptera), strepsirrhine primates, and tarsiers do not have a CGbeta gene, although they possess one copy of the LHbeta gene. The CGbeta gene first arose in the common ancestor of the anthropoid primates (New World monkeys, Old World monkeys, apes, and humans), after the anthropoids diverged from tarsiers. At least two subsequent duplication events occurred in the catarrhine primates, all of which possess multiple CGbeta copies. The LHbeta-CGbeta family of genes has undergone frequent gene conversion among the catarrhines, as well as periods of strong positive selection in the New World monkeys (platyrrhines). In addition, newly generated DNA sequences from the promoter of the CG alpha subunit gene indicate that platyrrhine monkeys use a different mechanism of alpha gene expression control than that found in catarrhines.

Bioactivity of recombinant prorelaxin from the marmoset monkey

The hormone relaxin (RLX) is generally present in the serum of humans and primates as a heterodimer, though some unprocessed prohormone may also be present. In order to test whether this proRLX is biologically relevant for human or primate physiology, recombinant marmoset monkey proRLX was synthesized in a baculovirus-infected cell system and tested in different bioassays. Marmoset proRLX is >70% identical to human H2 proRLX, especially in the so-called receptor-binding region of the B-peptide. The bioassay systems used were (a) cAMP production by human endometrial stromal cells and (b) cAMP production by the human monocyte cell line THP-1. In both bioassay systems recombinant proRLX showed comparable EC(50) values to pure porcine heterodimeric relaxin (porcine relaxin, 1.5-2.0 nM; marmoset prorelaxin 4.0-5.0 nM). Additionally, recombinant marmoset prorelaxin was shown to stimulate steroidogenesis in primary cultures of marmoset ovarian theca cells, though with a lower apparent activity than porcine relaxin. It thus appears that precursor processing of human or primate relaxin is not an essential prerequisite for the acquisition of bioactivity, as it is for the closely related hormone insulin, and that circulating prorelaxin is physiologically relevant.

Molecular remodeling of members of the relaxin family during primate evolution

Employing comparative analysis of the cDNA-coding sequences of the unique preprorelaxin of the Afro-lorisiform Galago crassicaudatus and the Malagasy lemur Varecia variegata and the relaxin-like factor (RLF) of G. crassicaudatus, we demonstrated distinct differences in the dynamics of molecular remodeling of both hormones during primate evolution. The lorisiform and lemuriform preprorelaxin sequences encoded identical hormones, providing the first endocrinological evidence for the monophyletic origin of all Strepsirrhini. Structural analysis revealed the lemuriform members of the relaxin family to be potentially bioactive single-gene products. In contrast to the "two-prong" relaxin receptor-binding motif (RELVR) present within the B-domains of other primate relaxins, strepsirrhine relaxin contained a unique "three-prong" motif (RRLIR) with highest sequence homology to the receptor-binding motif of the evolutionarily much older skate relaxin. In contrast to relaxin, the RLF molecule was highly conserved during primate evolution and contained within its B-domain the putative relaxin receptor-binding motif and a pentameric sequence implicated in binding to specific RLF receptors. Mutually exclusive expression of strepsirrhine preprorelaxin and RLF were observed in the fetal villous trophoblast cells of the strepsirrhine placenta and postpubertal testicular Leydig cells, respectively, reflecting distinct functional roles for both hormones within the reproductive tract of Strepsirrhini.