Expression of vascular endothelial growth factor isoforms and receptors Flt-1 and KDR during the peri-implantation period in the mink, Mustela vison

Multiple types of genomic variation contribute to adaptive traits in the mustelid subfamily Guloninae

Species of the mustelid subfamily Guloninae inhabit diverse habitats on multiple continents, and occupy a variety of ecological niches. They differ in feeding ecologies, reproductive strategies and morphological adaptations. To identify candidate loci associated with adaptations to their respective environments, we generated a de novo assembly of the tayra (Eira barbara), the earliest diverging species in the subfamily, and compared this with the genomes available for the wolverine (Gulo gulo) and the sable (Martes zibellina). Our comparative genomic analyses included searching for signs of positive selection, examining changes in gene family sizes, as well as searching for species-specific structural variants (SVs). Among candidate loci associated with phenotypic traits, we observed many related to diet, body condition and reproduction. For example, for the tayra, which has an atypical gulonine reproductive strategy of aseasonal breeding, we observe species-specific changes in many pregnancy-related genes. For the wolverine, a circumpolar hypercarnivore that must cope with seasonal food scarcity, we observed many changes in genes associated with diet and body condition. All types of genomic variation examined (single nucleotide polymorphisms, gene family expansions, structural variants) contributed substantially to the identification of candidate loci. This strongly argues for consideration of variation other than single nucleotide polymorphisms in comparative genomics studies aiming to identify loci of adaptive significance.

Effects of P4 Antagonist RU486 on VEGF and Its Receptors' Signaling during the In Vivo Transition from the Preovulatory to Periovulatory Phase of Ovarian Follicles

The development of an adequate blood vessel network is crucial for the accomplishment of ovarian follicle growth and ovulation, which is necessary to support the proliferative and endocrine functions of the follicular cells. Although the Vascular Endothelial Growth Factor (VEGF) through gonadotropins guides ovarian angiogenesis, the role exerted by the switch on of Progesterone (P4) during the periovulatory phase remains to be clarified. The present research aimed to investigate in vivo VEGF-mediated mechanisms by inducing the development of periovulatory follicles using a pharmacologically validated synchronization treatment carried out in presence or absence of P4 receptor antagonist RU486. Spatio-temporal expression profiles of VEGF, FLT1, and FLK1 receptors and the two major MAPK/ERKs and PI3K/AKT downstream pathways were analyzed on granulosa and on theca compartment. For the first time, the results demonstrated that in vivo administration of P4 antagonist RU486 inhibits follicular VEGF receptors' signaling mainly acting on the theca layer by downregulating the activation of ERKs and AKTs. Under the effect of RU486, periovulatory follicles' microarchitecture did not move towards the periovulatory stage. The present evidence provides new insights on P4 in vivo biological effects in driving vascular and tissue remodeling during the periovulatory phase.

Endometrial receptivity and embryo implantation in carnivores-commonalities and differences with other mammalian species

Endometrial receptivity and embryo implantation processes are a major point of pregnancy failure in many mammalian species, including humans. Although reproductive biology in many carnivore species remains enigmatic, the few that have been studied so far are invaluable comparative models. The goals of this review are to (1) summarize current data on the mechanisms involved in uterine receptivity and embryo implantation in carnivores, including commonalities and differences with other mammalian species and (2) identify research priorities to better understand a key phenomenon in a critical group of mammals. Besides unique reproductive traits in some carnivores (induced vs. spontaneous ovulation in cats, ovulation at the germinal vesicle stage in dogs), preimplantation embryo development is comparable with other orders. However, the timing of implantation varies, especially in species having an embryonic diapause. Mechanisms involved in endometrial receptivity and decidualization still remain to be fully understood, but specific markers have already been identified. Importantly, the use of endogenous hormones to control the ovarian activity may impact endometrial receptivity and subsequent embryo implantation. Next, research efforts should take advantage of advanced technologies to further study embryo implantation in carnivores and to provide more relevant models to reproductive medicine or for the conservation of rare and endangered species.

Do ovarian steroid hormones control the resumption of embryonic growth following the period of diapause in roe deer (Capreolus capreolus)?

Embryonic diapause in the European roe deer includes a period of five months from August to December in which embryonic development is extremely decelerated. Following exit from diapause, the embryo rapidly elongates and subsequently implants. In diapausing carnivores and marsupials, resumption of embryonic growth is regulated by ovarian steroid hormones. In the roe deer, the role of steroid hormones is not known to date. In the present study, progesterone (P4), estradiol-17β (E2) and total estrogens (E_tot) were determined in blood plasma and endometrium of roe deer shot in the course of regular huntings between September and December. Steroid hormone concentrations were correlated to the corresponding size of the embryo derived from ex vivo uterine flushing and to the date of sampling. The mean plasma concentrations of P4 (5.4 ± 0.2 ng/ml, mean ± SE, N = 87), E2 (24.3 ± 2.6 pg/ml, N = 86) and E_tot (21.7 ± 2.6 pg/ml, N = 78) remained constant over the sampling period and were not correlated to embryonic size. Likewise, endometrial concentrations of P4 (66.1 ± 6.5 ng/g), E2 (284.0 ± 24.43 pg/g) and, E_tot (440.9 ± 24.43 pg/g) showed no changes over time [corrected]. Therefore, it was concluded that ovarian steroid hormones do not play a determining role in resumption of embryonic growth following the period of diapause in the roe deer.

Transcriptome Changes in the Mink Uterus during Blastocyst Dormancy and Reactivation

Embryo implantation in the mink follows the pattern of many carnivores, in that preimplantation embryo diapause occurs in every gestation. Details of the gene expression and regulatory networks that terminate embryo diapause remain poorly understood. Illumina RNA-Seq was used to analyze global gene expression changes in the mink uterus during embryo diapause and activation leading to implantation. More than 50 million high quality reads were generated, and assembled into 170,984 unigenes. A total of 1684 differential expressed genes (DEGs) in uteri with blastocysts in diapause were compared to the activated embryo group (p < 0.05). Among these transcripts, 1527 were annotated as known genes, including 963 up-regulated and 564 down-regulated genes. The gene ontology terms for the observed DEGs, included cellular communication, phosphatase activity, extracellular matrix and G-protein couple receptor activity. The KEGG pathways, including PI3K-Akt signaling pathway, focal adhesion and extracellular matrix (ECM)-receptor interactions were the most enriched. A protein-protein interaction (PPI) network was constructed, and hub nodes such as VEGFA, EGF, AKT, IGF1, PIK3C and CCND1 with high degrees of connectivity represent gene clusters expected to play an important role in embryo activation. These results provide novel information for understanding the molecular mechanisms of maternal regulation of embryo activation in mink.

Comparative transcriptome analysis of embryo invasion in the mink uterus

INTRODUCTION

In mink, as many as 65% of embryos die during gestation. The causes and the mechanisms of embryonic mortality remain unclear. The purpose of our study was to examine global gene expression changes during embryo invasion in mink, and thereby to identify potential signaling pathways involved in implantation failure and early pregnancy loss.

METHODS

Illumina's next-generation sequencing technology (RNA-Seq) was used to analyze the differentially expressed genes (DEGs) in implantation (IMs) and inter-implantation sites (inter-IMs) of uterine tissue.

RESULTS

We identified a total of 606 DEGs, including 420 up- and 186 down-regulated genes in IMs compared to inter-IMs. Gene annotation analysis indicated multiple biological pathways to be significantly enriched for DEGs, including immune response, ECM complex, cytokine activity, chemokine activity and protein binding. The KEGG pathway including cytokine-cytokine receptor interaction, Jak-STAT, TNF and the chemokine signaling pathway were the most enriched. A gene network was constructed, and hub nodes such as CSF3, ICAM1, FOS, IL1B, IL8, CD14 and MYC were found through network analysis.

DISCUSSION

This report provides a valuable resource for understanding the mechanisms of embryo implantation in mink.

The enigma of embryonic diapause

Embryonic diapause – a period of embryonic suspension at the blastocyst stage – is a fascinating phenomenon that occurs in over 130 species of mammals, ranging from bears and badgers to mice and marsupials. It might even occur in humans. During diapause, there is minimal cell division and greatly reduced metabolism, and development is put on hold. Yet there are no ill effects for the pregnancy when it eventually continues. Multiple factors can induce diapause, including seasonal supplies of food, temperature, photoperiod and lactation. The successful reactivation and continuation of pregnancy then requires a viable embryo, a receptive uterus and effective molecular communication between the two. But how do the blastocysts survive and remain viable during this period of time, which can be up to a year in some cases? And what are the signals that bring it out of suspended animation? Here, we provide an overview of the process of diapause and address these questions, focussing on recent molecular data.

Efeito da iluminação constante sobre a placenta de ratas: um estudo morfológico, morfométrico e histoquímico

A presente pesquisa analisou o efeito da iluminação constante sobre a estrutura placentária de ratas, abordando parâmetros morfológicos, morfométricos e histoquímicos. Vinte ratas albinas foram submetidas aos seguintes tratamentos: 12hL/12hE por 60 dias, e acasaladas em seguida (GI); ausência de luz por 60 dias, e acasaladas em seguida (GII); iluminação constante por 60 dias, e acasaladas em seguida (GIII); iluminação constante por 60 dias, acasaladas em seguida e tratadas com melatonina (GIV). O estímulo luminoso foi em torno de 400 lux. A melatonina foi administrada na água (400mg/mL de etanol). Os resultados mostraram que histologicamente o GII apresentou vacuolização das células do trofospongio. Morfometricamente, o GIII apresentou camada do labirinto com redução no número de trofoblastos sinciciais e maior vascularização materno-fetal, hiperplasia e hipertrofia das células trofoblásticas gigantes, uma maior média da área total do disco placentário; porém, na camada de trofospongio, as células trofoblásticas e trofoblastos sinciciais não diferiram nos grupos experimentais. As placentas do GIV foram semelhantes às do GI. Histoquimicamente não houve alterações nas fibras colágenas, elásticas, reticulares e glicosaminoglicanas ácidas. Em conclusão, a iluminação constante promove alterações morfológicas e morfométricas na placenta de ratas, podendo acarretar redução funcional e restrições ao crescimento fetal. Essas alterações são abolidas pela reposição de melatonina.

Effect of antiprogesterone RU486 on VEGF expression and blood vessel remodeling on ovarian follicles before ovulation

Background

The success of ovarian follicle growth and ovulation is strictly related to the development of an adequate blood vessel network required to sustain the proliferative and endocrine functions of the follicular cells. Even if the Vascular Endothelial Growth Factor (VEGF) drives angiogenesis before ovulation, the local role exerted by Progesterone (P₄) remains to be clarified, in particular when its concentration rapidly increases before ovulation.

Aim

This in vivo study was designed to clarify the effect promoted by a P₄ receptor antagonist, RU486, on VEGF expression and follicular angiogenesis before ovulation, in particular, during the transition from pre to periovulatory follicles induced by human Chorionic Gonadotropins (hCG) administration.

Material and Methods

Preovulatory follicle growth and ovulation were pharmacologically induced in prepubertal gilts by combining equine Chorionic Gonadotropins (eCG) and hCG used in the presence or absence of RU486. The effects on VEGF expression were analyzed using biochemical and immunohistochemical studies, either on granulosa or on theca layers of follicles isolated few hours before ovulation. This angiogenic factor was also correlated to follicular morphology and to blood vessels architecture.

Results and Conclusions

VEGF production, blood vessel network and follicle remodeling were impaired by RU486 treatment, even if the cause-effect correlation remains to be clarified. The P₄ antagonist strongly down-regulated theca VEGF expression, thus, preventing most of the angiogenic follicle response induced by hCG. RU486-treated follicles displayed a reduced vascular area, a lower rate of endothelial cell proliferation and a reduced recruitment of perivascular mural cells. These data provide important insights on the biological role of RU486 and, indirectly, on steroid hormones during periovulatory follicular phase. In addition, an in vivo model is proposed to evaluate how periovulatory follicular angiogenesis may affect the functionality of the corpus luteum (CL) and the success of pregnancy.

Dexamethasone-induced eosinopenia is associated with lower progesterone production in cattle

Eosinophilic cells accumulate in the capillaries of the bovine Graafian follicle shortly before ovulation and in the early developing corpus luteum (CL). Suppressing the migration of these eosinophilic cells by dexamethasone allowed us to evaluate their possible function in the CL development. Brown Swiss cows (n = 10) were randomly subdivided into two groups (n = 5). Every group was used once as control group and once as experimental group with two oestrous cycles between each treatment. Eighteen hours (h) after oestrus synchronization, dexamethasone or saline was given. Ovulation was induced 24 h later with gonadotropin-releasing hormone. Another injection of dexamethasone or saline was given 12 h later. Eosinophilic cells in the blood were counted daily until day 7 after the first dexamethasone injection. The collection of ovaries took place at days 1, 2 and 5. Gene expression, protein concentration and location of angiogenic factors, chemokines, insulin-like growth factor 1 (IGF1) and eosinophilic cells were studied. No eosinophilic cells were found in the CL of the treatment group. Blood progesterone decreased significantly in the dexamethasone group from day 8 to 17. The protein concentration of FGF2 increased significantly in CL tissue at day 2 and VEGFA decreased. Local IGF1 gene expression in the CL was not regulated. We assume from our data that the migration of eosinophilic cells into the early CL is not an essential, but an important stimulus for angiogenesis during early CL development in cattle.

The expression of vascular endothelial growth factor and its receptors (flt1/fms, flk1/KDR, flt4) and vascular endothelial growth inhibitor in the bovine uterus during the sexual cycle and their correlation with serum sex steroids

The present study was conducted to demonstrate of the immunohistochemical localization of vascular endothelial growth factor (VEGF) and its receptors (flt1/fms, flk1/KDR and flt4) as well as vascular endothelial growth inhibitor (VEGI) and to determine the correlation of VEGF and its receptors and VEGI with serum sex steroids (estrogen and progesterone) in the bovine uterus during the sexual cycle. The stage of the estrous cycle in 30 Holstein cattle was assessed based on the gross and histological appearance of the ovaries and uterus and on blood steroid hormone levels. Tissue samples obtained from the uterus were fixed in 10% formaldehyde for routine histological processing. During both follicular and luteal phases, positive cytoplasmic and membrane staining was achieved for VEGF and its receptors (flt1/fms, flk1/KDR and flt4) as well as VEGI in the luminal and glandular epithelial cells, the connective tissue and smooth muscle cells, and the vascular endothelial cells and smooth muscle cells in the uterus. The intensity, proportional and total scores determined for VEGF and its receptors (flt1/fms and flt4) as well as VEGI were greater in the luminal and glandular epithelial cells compared to the connective tissue and smooth muscle cells (P < 0.05). Furthermore, the number and intensity of the flk1/KDR positive cells were greater among the connective tissue cells compared to the luminal and glandular epithelial cells (P < 0.05). As a result, it was determined that the expression of VEGF and its receptors as well as VEGI in the bovine uterus during the follicular and luteal phases varied with different cell types. This suggests that depending on the stage of the sexual cycle, these factors may mediate the establishment of an appropriate environment for the nutritional supply and implantation of the embryo primarily due to the stimulation of angiogenesis but also through the increase in the secretory activity of the epithelial cells in the uterus. Furthermore, this indicates that ovarian steroid hormones play a significant role in regulating the expression of VEGF and its receptors as well as VEGI.

Spatiotemporal expression pattern of progranulin in embryo implantation and placenta formation suggests a role in cell proliferation, remodeling, and angiogenesis

Embryo implantation in the mink is preceded by a variable but obligate period of delay in development. Under the influence of progesterone and unknown luteal factors, the mink embryo implants 11–13 days following its exit from diapause. Recent work suggests that progranulin, a growth factor and secreted glycoprotein, is involved in trophoblast proliferation, placental development and endometrial differentiation in the mouse. Using the mink model of delayed implantation and endotheliochorial placentation, we examined the spatiotemporal distribution of progranulin in trophoblast and endometrium during pre- and early post-implantation gestationin vivo. A partial sequence of the mink progranulin gene was cloned and sequenced. Comparative sequence analysis revealed that exons 1 and 2 of mink progranulin share 86.6, 82.4, and 94.9% of nucleic acid sequence identity with the human, mouse, and dog sequences respectively, and indicated that the invariable residues of the cysteine-rich motifs of progranulin are well conserved in the mink sequence. Byin situhybridization, we show that mink progranulin transcript is present in the cytotrophoblast and in epithelial and stromal endometrial cells at the site of implantation and during early placental formation. Immunohistochemistry revealed the progranulin protein to be strongly expressed in endometrial luminal and glandular epithelium around the time of implantation. In the incipient labyrinth, progranulin expression is localized to cytotrophoblasts and fetal capillaries, as well as to the hypertrophied maternal endothelial cells. This study demonstrates that high levels of progranulin expression correspond to active cell proliferation, remodeling, and angiogenesis occurring during the establishment of the placenta in the mink.

Effect of the luteinising hormone surge on regulation of vascular endothelial growth factor and extracellular matrix-degrading proteinases and their inhibitors in bovine follicles

The aim of the present study was to evaluate the pattern of regulation of vascular endothelial growth factor (VEGF)-A (isoforms 121, 165, 189), VEGF receptor tyrosine kinases (VEGF-R1 and VEGF-R2), matrix metalloproteinase (MMP)-1, MMP-2, MMP-14, MMP-19, tissue-specific inhibitor of metalloproteinases (TIMP)-1, TIMP-2, tissue plasminogen activator (tPA), urokinase plasminogen activator (uPA), urokinase plasminogen activator receptor (uPAR) and plasminogen activator inhibitor-1 (PAI-1) in time-defined follicle classes before (0 h) and after the application of gonadotrophin-releasing hormone (GnRH). Bovine ovaries containing periovulatory follicles or new corpora lutea (CL; Days 1-2) were collected 0, 4, 10, 20 and 25 h (follicles) or 60 h (CL) after the injection of GnRH. Transcripts of VEGF isoforms (VEGF(121), VEGF(165), VEGF(189)) were upregulated 4 h after GnRH injection (during the luteinising hormone (LH) surge) and decreased thereafter to lowest levels around ovulation. All VEGF isoforms and their receptors were upregulated again after ovulation. The VEGF peptide concentration in follicular fluid decreased 20 h after GnRH injection, followed by an increase in follicles 25 h after GnRH. Expression of MMP-1 mRNA increased rapidly 4 h after GnRH injection and remained high during the entire experimental period. In contrast, MMP-19 mRNA increased significantly only after ovulation. Expression of TIMP-1 mRNA increased 4 h after GnRH and again after ovulation. Expression of tPA mRNA increased 4 h after GnRH and remained high during the entire experimental period, whereas expression of uPA transcripts increased significantly only after ovulation. Both uPAR and PAI-1 mRNA levels increased in follicles 4 h after GnRH and again after ovulation. The amount of MMP-1 protein (immunolocalisation) increased in follicles 10 h after GnRH: additional staining was observed in the granulosa cell layer. In conclusion, the temporal and spatial pattern of regulation of VEGF and extracellular matrix-degrading proteinases during periovulation suggests they are important mediators of the LH-dependent rupture of bovine follicles and for early CL formation (angiogenesis).

Cytokines: Important for implantation?

PROBLEM

Cytokines are obviously very important in an established pregnancy, but what about human embryo implantation?

METHODS

Literature review.

RESULTS

We first discuss the necessity and limits of animal models, and then review the few cytokines which have been demonstrated by knock-out methods to be absolutely necessary for embryo implantation using in animal models. We then review what is known or discussed about the role of other cytokines as deduced from quantitative and/or qualitative dysregulation in animals and in humans.

CONCLUSIONS

Cytokines are indeed involved in implantation as they are in ongoing pregnancy and delivery. Relevance to infertility and recurrent pregnancy loss is discussed.

The Peroxisome Proliferator-Activated Receptor Gamma Regulates Trophoblast Cell Differentiation in Mink (Mustela vison)1

Nuclear receptors of the peroxisome proliferator-activated receptor (PPAR) family are implicated in implantation and early placental formation. In carnivores, the trophoblast invades to develop intimate contact with the endothelial cells of the maternal circulation, resulting in an endothelio-chorial form of placentation. Spatio-temporal investigation demonstrated that peroxisome proliferator-activated receptor gamma (PPARG) was strongly and specifically expressed in the mink trophoblast at the time of formation of the syncytiotrophoblast during early implantation, and in trophoblast of the placental labyrinth. The retinoid-X-receptor alpha (RXRA), the heterodimeric partner of PPARG in transcriptional regulation, is, with very few exceptions, co-expressed with PPARG in mink trophoblast. We used mink trophoblast cell lines together with a natural (15-deoxy-delta(12,14)-prostaglandin J(2) ) or a synthetic (troglitazone) PPARG ligand to demonstrate that PPARG is an authentic regulator of gene expression in this tissue. Ligand-activated PPARG stimulated transcription of the PPRE-luc reporter gene transfected into these cell lines. The prostaglandin-induced morphologic changes were accompanied by attenuation in cell proliferation, an increase in PPARG mRNA and protein levels, and the appearance of enlarged and multinuclear cells. Furthermore, 15-deoxy-delta(12,14)-prostaglandin J(2) stimulated the expression of invasion-related genes in trophoblast cells, namely, adipophilin and osteopontin. The results demonstrate that PPARG ligands attenuate proliferation and induce differentiation of mink trophoblast cells to the multlinuclear phenotype. The upregulation of differentiation-specific genes in the placenta under the influence of PPARG ligands provides a mechanism by which blastocyst and endometrial prostanoids regulate implantation, as well as the formation and maintenance of the placenta.

Transcriptional regulation of uterine vascular endothelial growth factor during early gestation in a carnivore model, Mustela vison

Vascular endothelial growth factor (VEGF) is an essential angiogenic signaling element that acts through its two tyrosine kinase receptors, inducing both proliferation of endothelial cells and vascular permeability. Given the importance of vasculogenesis and angiogenesis to early pregnancy, it is of interest to understand the mechanisms regulating vascular development at this stage. We previously demonstrated that VEGF and receptors are up-regulated during embryo implantation in an unique animal model, the mink, a species displaying obligate embryonic diapause. Herein we examined the role of prostaglandin E2 (PGE(2)) as a regulator of VEGF during early pregnancy and established the mechanisms of this regulation. We demonstrate that activated embryos secrete PGE(2) and that expression of PGE synthase protein in the uterus is dependent upon direct contact with invading trophoblast cells during implantation. Using mink uterine stromal cells transfected with mink VEGF promoter driving the luciferase reporter gene, we show that PGE(2) induces promoter transactivation and that this response can be eliminated by blockade of protein kinase A. Treatment with antagonists to PGE(2) receptors EP2 and EP4 eliminated the PGE(2)-induced response in transfected cells. Deletional studies of the promoter revealed that a region of 99 bp upstream of the transcription start site is required for PGE(2)-induced transactivation. Mutation of an AP2/Sp1 cluster, found within the 99 bp, completely eliminated the PGE(2) response. Furthermore, chromatin immunoprecipitation assays confirmed binding of the AP2 and Sp1 transcription factors to the endogenous mink VEGF promoter in uterine cells. PGE(2) stimulated acetylation of histone H3 associated with the promoter region containing the AP2/Sp1 cluster. Taken together, these results demonstrate that PGE(2) plays an important role in regulating uterine and thus placental vascular development, acting through its receptors EP2 and EP4, provoking protein kinase A activation of AP2 and Sp1 as well as acetylation of histone H3 to transactivate the VEGF promoter.