Recombinant entactin promotes mouse primary trophoblast cell adhesion and migration through the Arg-Gly-Asp (RGD) recognition sequence

CDX2 downregulation in mouse mural trophectoderm during peri‐implantation is heteronomous, dependent on the YAP‐TEAD pathway and controlled by estrogen‐induced factors

Purpose

To investigate the transition of CDX2 expression patterns in mouse trophectoderm (TE) and its regulatory mechanisms during implantation.

Methods

Mouse E3.5–4.5 blastocysts were used to immunostain CDX2, YAP, TEAD4, and ESRRB. Endogenous estrogen signaling was perturbed by administrating estrogen receptor antagonist ICI 182,780 or ovariectomy followed by administration of progesterone and β‐estradiol to elucidate the relationship between the transition of CDX2 expression patterns and ovarian estrogen‐dependent change in the uterine environment.

Results

CDX2 expression was gradually downregulated in the mural TE from E4.0 in vivo, whereas CDX2 downregulation was not observed in blastocysts cultured in KSOM. Fetal bovine serum (FBS) supplementation in KSOM induced CDX2 downregulation independently of blastocyst attachment to dishes. CDX2 downregulation in the mural TE was repressed by administration of ICI 182,780 or by ovariectomy, and administration of β‐estradiol into ovariectomized mice retriggered CDX2 downregulation. Furthermore, Cdx2 expression in the mural TE might be controlled by the YAP‐TEAD pathway.

Conclusions

CDX2 downregulation was induced heteronomously in the mural TE from E4.0 by uterus‐derived factors, the secretion of which was stimulated by ovarian estrogen.

Differential Expression Pattern of Goat Uterine Fluids Extracellular Vesicles miRNAs during Peri-Implantation

Early pregnancy failure occurs when a mature embryo attaches to an unreceptive endometrium. During the formation of a receptive endometrium, extracellular vesicles (EVs) of the uterine fluids (UFs) deliver regulatory molecules such as small RNAs to mediate intrauterine communication between the embryo and the endometrium. However, profiling of small RNAs in goat UFs’ EVs during pregnancy recognition (day 16) has not been carried out. In this study, EVs were isolated from UFs on day 16 of the estrous cycle or gestation. They were isolated by Optiprep™ Density G radient (ODG) and verified by transmission electron microscopy (TEM), nanoparticle tracking analysis (NTA), and Western blotting. Immunostaining demonstrated that CD63 was present both in the endometrial epithelium and glandular epithelium, and stain intensity was greater in the pregnant endometrium compared to the non-pregnant endometrium. Small RNA sequencing revealed that UFs’ EVs contained numerous sRNA families and a total of 106 differentially expressed miRNAs (DEMs). Additionally, 1867 target genes of the DEMs were obtained, and miRNA–mRNA interaction networks were constructed. GO and KEGG analysis showed that miRNAs were significantly associated with the formation of a receptive endometrium and embryo implantation. In addition, the fluorescence in situ hybridization assay (FISH) showed that chi-miR-451-5p was mainly expressed in stromal cells of the endometrium and a higher level was detected in the endometrial luminal epithelium in pregnant states. Moreover, the dual-luciferase reporter assay showed that chi-miR-451-5p directly binds to PSMB8 and may play an important role in the formation of a receptive endometrium and embryo implantation. In conclusion, these results reveal that UFs’ EVs contain various small RNAs that may be vital in the formation of a receptive endometrium and embryo implantation.

Advantages of the outgrowth model for evaluating the implantation competence of blastocysts

The implantation process is highly complex and difficult to mimic in vitro, and a reliable experimental model of implantation has yet to be established. Many researchers have used embryo transfer (ET) to assess implantation potential; however, ET with pseudopregnant mice requires expert surgical skills and numerous sacrificial animals. To overcome those economic and ethical problems, several researchers have tried to use outgrowth models to evaluate the implantation potential of embryos. Many previous studies, as well as our experiments, have found significant correlations between blastocyst outgrowth in vitro and implantation in utero by ET. This review proposes the blastocyst outgrowth model as a possible alternative to animal experimentation involving ET in utero. In particular, the outgrowth model might be a cost- and time-effective alternative method to ET for evaluating the effectiveness of culture conditions or treatments. An advanced outgrowth model and further culture of outgrowth embryos could provide a subtle research model of peri- and postimplantation development, excluding maternal effects, and thereby could facilitate progress in assisted reproductive technologies. Recently, we found that outgrowth embryos secreted extracellular vesicles containing specific microRNAs. The function of microRNAs from outgrowth embryos should be elucidated in further researches.

The Role of MicroRNAs in Mammalian Fertility: From Gametogenesis to Embryo Implantation

The genetic codes inscribed during two key developmental processes, namely gametogenesis and embryogenesis, are believed to determine subsequent development and survival of adult life. Once the embryo is formed, its further development mainly depends on its intrinsic characteristics, maternal environment (the endometrial receptivity), and the embryo–maternal interactions established during each phase of development. These developmental processes are under strict genetic regulation that could be manifested temporally and spatially depending on the physiological and developmental status of the cell. MicroRNAs (miRNAs), one of the small non-coding classes of RNAs, approximately 19–22 nucleotides in length, are one of the candidates for post-transcriptional developmental regulators. These tiny non-coding RNAs are expressed in ovarian tissue, granulosa cells, testis, oocytes, follicular fluid, and embryos and are implicated in diverse biological processes such as cell-to-cell communication. Moreover, accumulated evidences have also highlighted that miRNAs can be released into the extracellular environment through different mechanisms facilitating intercellular communication. Therefore, understanding miRNAs mediated regulatory mechanisms during gametogenesis and embryogenesis provides further insights about the molecular mechanisms underlying oocyte/sperm formation, early embryo development, and implantation. Thus, this review highlights the role of miRNAs in mammalian gametogenesis and embryogenesis and summarizes recent findings about miRNA-mediated post-transcriptional regulatory mechanisms occurring during early mammalian development.

Embryonic Cul4b is important for epiblast growth and location of primitive streak layer cells

Cul4b-null (Cul4bΔ/Y) mice undergo growth arrest and degeneration during the early embryonic stages and die at E9.5. The pathogenic causes of this lethality remain incompletely characterized. However, it has been hypothesized that the loss of Cul4b function in extraembryonic tissues plays a key role. In this study, we investigated possible causes of death for Cul4b-null embryos, particularly in regard to the role of embryonic Cul4b. First, we show that the loss of embryonic Cul4b affects the growth of the inner cell mass in vitro and delays epiblast development during the gastrulation period at E6.5~E7.5 in vivo, as highlighted by the absence of the epiblastic transcription factor Brachyury from E6.5~E7.5. Additionally, at E7.5, strong and laterally expanded expression of Eomes and Fgf8 signaling was detected. Sectioning of these embryos showed disorganized primitive streak layer cells. Second, we observed that Mash2-expressing cells were present in the extraembryonic tissues of Cul4b-deficient embryos at E6.5 but were absent at E7.5. In addition, the loss of Cul4b resulted in decreased expression of cyclin proteins, which are required for the cell cycle transition from G1 to S. Taken together, these observations suggest that the embryonic expression of Cul4b is important for epiblast growth during E6.5~E7.5, and the loss of Cul4b results in either delayed growth of the epiblast or defective localization of primitive streak layer cells. As a result, the signaling activity mediated by the epiblast for subsequent ectoplacental cone development is affected, with the potential to induce growth retardation and lethality in Cul4bΔ/Y embryos.

Nidogen-1 is a novel extracellular ligand for the NKp44 activating receptor

The release of soluble ligands of activating Natural Killer (NK) cell receptors may represent a regulatory mechanism of NK cell function both in physiologic and in pathologic conditions. Here, we identified the extracellular matrix protein Nidogen-1 (NID1) as a ligand of NKp44, an important activating receptor expressed by activated NK cells. When released as soluble molecule, NID1 regulates NK cell function by modulating NKp44-induced IFN-γ production or cytotoxicity. In particular, it also modulates IFN-γ production induced by Platelet-Derived Growth Factor (PDGF)-DD following NKp44 engagement. We also show that NID1 may be present at the cell surface. In this form or when bound to a solid support (bNID1), NID1 fails to induce NK cell cytotoxicity or cytokine release. However, analysis by mass spectrometry revealed that exposure to bNID1 can induce in human NK cells relevant changes in the proteomic profiles suggesting an effect on different biological processes.

Discovering Cell-Adhesion Peptides in Tissue Engineering: Beyond RGD

As an alternative to natural extracellular matrix (ECM) macromolecules, cell-adhesion peptides (CAPs) have had tremendous impact on the design of cell culture platforms, implants, and wound dressings. However, only a handful of CAPs have been utilized. The discrepancy in ECM composition strongly affects cell behavior, so it is paramount to reproduce such differences in synthetic systems. This Opinion article presents strategies inspired from high-throughput screening techniques implemented in drug discovery to exploit the potential of a growing CAP library. These strategies are expected to promote the use of a broader spectrum of CAPs, which in turn could lead to improved cell culture models, implants, and wound dressings.

Molecular and cellular events during blastocyst implantation in the receptive uterus: clues from mouse models

The success of implantation is an interactive process between the blastocyst and the uterus. Synchronized development of embryos with uterine differentiation to a receptive state is necessary to complete pregnancy. The period of uterine receptivity for implantation is limited and referred to as the “implantation window”, which is regulated by ovarian steroid hormones. Implantation process is complicated due to the many signaling molecules in the hierarchical mechanisms with the embryo-uterine dialogue. The mouse is widely used in animal research, and is uniquely suited for reproductive studies, i.e., having a large litter size and brief estrous cycles. This review first describes why the mouse is the preferred model for implantation studies, focusing on uterine morphology and physiological traits, and then highlights the knowledge on uterine receptivity and the hormonal regulation of blastocyst implantation in mice. Our recent study revealed that selective proteolysis in the activated blastocyst is associated with the completion of blastocyst implantation after embryo transfer. Furthermore, in the context of blastocyst implantation in the mouse, this review discusses the window of uterine receptivity, hormonal regulation, uterine vascular permeability and angiogenesis, the delayed-implantation mouse model, morphogens, adhesion molecules, crosslinker proteins, extracellular matrix, and matricellular proteins. A better understanding of uterine and blastocyst biology during the peri-implantation period should facilitate further development of reproductive technology.

Water-extracted Perilla frutescens increases endometrial receptivity though leukemia inhibitory factor-dependent expression of integrins

The leaves and stems of Perilla frutescens var. acuta Kudo (PF) have been used to prevent threatened abortion in traditional medicine in the East Asian countries. Because reduced receptivity of endometrium is a cause of abortion, we analyzed the action of PF on the endometrial receptivity. PF increased the level of leukemia inhibitory factor (LIF), a major cytokine regulating endometrial receptivity, and LIF receptor in human endometrial Ishikawa cells. The PF-induced LIF expression was mediated by c-jun N-terminal kinase (JNK) and p38 pathways. Adhesion between Ishikawa cells and trophoblastic JAr cells stimulated by PF treatment was abolished by knock down of LIF expression or antagonism of LIFR. In addition, the expressions of integrin β3 and β5 were increased by PF treatment in Ishikawa cells. The PF-induced expression of integrin β3 and β5 was reduced with an LIFR antagonist. Neutralization of both integrins successfully blocked PF-stimulated adhesion of JAr cells and Ishikawa cells. These results suggest that PF enhanced the adhesion between Ishikawa cells and JAr cells by increasing the expression of integrin β3 and β5 via an LIF-dependent pathway. Given the importance of endometrial receptivity in successful pregnancy, PF can be a novel and effective candidate for improving pregnancy rate.

Impaired female fertility in tubulointerstitial antigen-like 1-deficient mice

Tubulointerstitial nephritis antigen-like 1 (Tinagl1, also known as adrenocortical zonation factor 1 [AZ-1] or lipocalin 7) is a matricellular protein. Previously, we demonstrated that Tinagl1 expression was restricted to extraembryonic regions during the postimplantation period and detected marked expression in mouse Reichert's membranes. In uteri, Tinagl1 is markedly expressed in the decidual endometrium during the postimplantation period, suggesting that it plays a physical and physiological role in embryo development and/or decidualization of the uterine endometrium during pregnancy. In the present study, in order to determine the role of Tinagl1 during embryonic development and pregnancy, we generated Tinagl1-deficient mice. Although Tinagl1(-/-) embryos were not lethal during development to term, homologous matings of Tinagl1(-/-) females and Tinagl1(-/-) males showed impaired fertility during pregnancy, including failure to carry pregnancy to term and perinatal lethality. To examine ovarian function, ovulation was induced with equine chorionic gonadotropin (eCG) and human chorionic gonadotropin (hCG); the number of ovulated oocytes did not differ between Tinagl1(-/-) and Tinagl1(flox/flox). In vitro fertilization followed by embryo culture also demonstrated the normal developmental potential of Tinagl1-null embryos during the preimplantation period. Our results demonstrate that Tinagl1 deficiency affects female mice and results in subfertility phenotypes, and they suggest that although the potential of Tinagl1(-/-) oocytes is normal, Tinagl1 is related to fertility in adult females but is not essential for either fertilization or preimplantation development in vitro.

Molecular and cellular events involved in the completion of blastocyst implantation

Blastocyst implantation is an interactive process between the embryo and the uterus. The synchronization of embryonic development with uterine differentiation to a receptive state is essential for a successful pregnancy. The period of uterine receptivity for implantation is limited. Although implantation involves the interaction of numerous signaling molecules, our understanding of the hierarchical mechanisms that coordinate with the embryo-uterine dialogue is not yet sufficient to prevent infertility caused by implantation failure. This review highlights our knowledge on uterine receptivity and hormonal regulation of blastocyst implantation in mice. We also discuss the adhesion molecules, cross-linker proteins, extracellular proteins, and matricellular proteins involved in blastocyst implantation. Furthermore, our recent study reveals that selective proteolysis in an activated blastocyst is associated with the completion of blastocyst implantation after embryo transfer. A better understanding of uterine and blastocyst biology during the peri-implantation period would facilitate further development of reproductive technology.

Expression of genes encoding extracellular matrix proteins: a macroarray study

Endometrial cancer (EC) is one of the most common gynecological malignancies in Poland, with well-established risk factors. Genetic instability and molecular alterations responsible for endometrial carcinogenesis have been systematically investigated. The aim of the present study was to investigate, by means of cDNA macroarrays, the expression profiles of genes encoding extracellular matrix (ECM) proteins in ECs. Tissue specimens were collected during surgical procedures from 40 patients with EC, and control tissue was collected from 9 patients with uterine leiomyomas. RNA was isolated and RT-PCR with radioisotope-labeled cDNA was performed. The levels of ECM protein gene expression in normal endometrial tissues were compared to the expression of these genes in EC specimens. Statistically significant differences in gene expression, stratified by clinical stage of the ECs, were detected for aggrecan, vitronectin, tenascin R, nidogen and two collagen proteins: type VIII chain α1 and type XI chain α2. All of these proteins were overexpressed in stage III endometrial carcinomas compared to levels in stage I and II uterine neoplasms. In conclusion, increased expression of genes encoding ECM proteins may play an important role in facilitating accelerated disease progression of human ECs.

Comparative Analysis of Glycogene Expression in Different Mouse Tissues Using RNA-Seq Data

Glycogenes regulate a wide array of biological processes in the development of organisms as well as different diseases such as cancer, primary open-angle glaucoma, and renal dysfunction. The objective of this study was to explore the role of differentially expressed glycogenes (DEGGs) in three major tissues such as brain, muscle, and liver using mouse RNA-seq data, and we identified 579, 501, and 442 DEGGs for brain versus liver (BvL579), brain versus muscle (BvM501), and liver versus muscle (LvM442) groups. DAVID functional analysis suggested inflammatory response, glycosaminoglycan metabolic process, and protein maturation as the enriched biological processes in BvL579, BvM501, and LvM442, respectively. These DEGGs were then used to construct three interaction networks by using GeneMANIA, from which we detected potential hub genes such as PEMT and HPXN (BvL579), IGF2 and NID2 (BvM501), and STAT6 and FLT1 (LvM442), having the highest degree. Additionally, our community analysis results suggest that the significance of immune system related processes in liver, glycosphingolipid metabolic processes in the development of brain, and the processes such as cell proliferation, adhesion, and growth are important for muscle development. Further studies are required to confirm the role of predicted hub genes as well as the significance of biological processes.

Uterine receptivity and embryo-uterine interactions in embryo implantation: lessons from mice

Implantation is a process of the first feto-maternal encounter in the uterus. A competent blastocyst and a receptive uterus are critical for successful implantation. For an acquisition of uterine receptivity, the following conditions need to be satisfied in the uterine environments: the endometrial preparation with stromal proliferation and epithelial differentiation in the pre-receptive phase and proper interactions between the uterus and blastocyst later in the phase. Focusing on these points and primarily referring to the mouse in vivo evidence, this review article has shown detailed molecular mechanisms for successful implantation.

PS integrins and laminins: key regulators of cell migration during Drosophila embryogenesis

During embryonic development, there are numerous cases where organ or tissue formation depends upon the migration of primordial cells. In the Drosophila embryo, the visceral mesoderm (vm) acts as a substrate for the migration of several cell populations of epithelial origin, including the endoderm, the trachea and the salivary glands. These migratory processes require both integrins and laminins. The current model is that αPS1βPS (PS1) and/or αPS3βPS (PS3) integrins are required in migrating cells, whereas αPS2βPS (PS2) integrin is required in the vm, where it performs an as yet unidentified function. Here, we show that PS1 integrins are also required for the migration over the vm of cells of mesodermal origin, the caudal visceral mesoderm (CVM). These results support a model in which PS1 might have evolved to acquire the migratory function of integrins, irrespective of the origin of the tissue. This integrin function is highly specific and its specificity resides mainly in the extracellular domain. In addition, we have identified the Laminin α1,2 trimer, as the key extracellular matrix (ECM) component regulating CVM migration. Furthermore, we show that, as it is the case in vertebrates, integrins, and specifically PS2, contributes to CVM movement by participating in the correct assembly of the ECM that serves as tracks for migration.

Nidogen plays a role in the regenerative axon growth of adult sensory neurons through Schwann cells

We previously reported that nidogen is an extracellular matrix protein regulating Schwann cell proliferation and migration. Since Schwann cells play a critical role in peripheral nerve regeneration, nidogen may play a role in it via regulation of Schwann cells. Here, we demonstrate direct evidence that nidogen induces elongation of regenerative axon growth of adult sensory neurons, and that the effect is Schwann cell dependent. Continuous infusion of recombinant ectodomain of tumor endothelial marker 7, which specifically blocks nidogen function in Schwann cells, suppressed regenerative neurite growth in a sciatic nerve axotomy model. Taken together, it is likely that nidogen is required for proper regeneration of peripheral nerves after injury.

Nidogens-Extracellular matrix linker molecules

Nidogens/entactins are a family of highly conserved, sulfated glycoproteins. Biochemical studies have implicated them as having a major structural role in the basement membrane. However despite being ubiquitous components of this specialized extracellular matrix and having a wide spectrum of binding partners, genetic analysis has shown that they are not required for the overall architecture of the basement membrane. Rather in development they play an important role in its stabilization especially in tissues undergoing rapid growth or turnover. Nidogen breakdown has been implicated as a key event in the basement membrane degradation occurring in mammary gland involution. A number of studies, most compellingly those in C. elegans, demonstrated that nidogens may have other nonstructural roles and be involved in axonal pathfinding and synaptic transmission.

Nidogen is a prosurvival and promigratory factor for adult Schwann cells

Schwann cells provide a favorable microenvironment for successful regeneration of the injured peripheral nerve. Even though the roles of extracellular matrix proteins in the Schwann cell physiology have long been studied, the precise function of nidogen, a ubiquitous component of the basal lamina, in Schwann cells is unknown. In this study, we show that the protein and mRNA messages for nidogens are up-regulated in the sciatic nerve after sciatic nerve transection. We demonstrate that recombinant nidogen-1 increased the process formation of Schwann cells cultured from adult rat sciatic nerves and that nidogen-1 prevented Schwann cells from serum-deprivation-induced death. In addition, nidogen-1 promoted spontaneous migration of Schwann cells in two-independent migration assays. The Schwann cell responses to the recombinant nidogen-1 were specific because the nidogen-binding ectodomain of tumor endothelial marker 7 inhibited the nidogen responses without affecting Schwann cell response to laminin. Finally, we found that beta1 subunit-containing integrins play a key role in the nidogen-induced process formation, survival, and migration of Schwann cells. Altogether, these results indicate that nidogen has a prosurvival and promigratory activity on Schwann cells in the peripheral nerve.

Differential expression of entactin-1/nidogen-1 and entactin-2/nidogen-2 in myogenic differentiation

Here, we show that entactin-2 expression is strongly, but transiently, induced in myogenic differentiation. Treatment of C2C12 myoblasts with actinomycin D in parallel to the induction of differentiation could demonstrate that this is due to enhanced transcription of the entactin-2 gene. Furthermore, treatment with the translation inhibitor cycloheximide could show that entactin-2 is a primary response gene. As p38 MAP kinase is an important regulator of myogenic differentiation, we also analyzed the possibility that entactin-2 might be a target of this pathway. However, using various p38 MAPK inhibitors, we could not detect involvement of p38 in entactin-2 up-regulation. Most remarkably, expression of the entactin-2 homolog entactin-1 dramatically declined in myogenesis, suggesting different functions of the two entactins in this process. A similar effect was seen in primary myoblasts isolated from two different mouse strains. Expression of high levels of entactin-1 in myoblasts using a retroviral expression system led to a higher proliferation rate both in growth and in differentiation medium and to reduced expression of various myogenic differentiation markers after the induction of differentiation. Furthermore, decreased expression of the entactin-2 gene after treatment of the cells with ent-2-specific siRNA preparation led to reduced expression of the cell cycle inhibitor p21. These data suggest important and distinct functions of entactin-1 and -2 in myogenic differentiation.

The role of recombinant proteins in the development of serum-free media

Early developments in serum-free media led to a variety of formulations in which components normally provided in serum and required for growth (insulin, transferrin, lipid supplements, trace elements) and poorly defined components (extracts, hydrolysates) were added to defined basal media. These additives were mostly animal-derived. Given recent concerns about TSEs (transmissible spongiform encephalopathies) and other adventitious agents, the drive in media formulations must be towards elimination of animal-origin materials while maintaining cell line productivity. The progress made towards removing animal-derived components and the use of recombinant proteins in serum-free media for mammalian cells is reviewed.

Expression of nidogens in rat uterus and embryo during decidualization and implantation

The purpose of this study was to demonstrate the expression of nidogen-1 and nidogen-2 and their possible role in decidualization and implantation events during early pregnancy in rats. The tissue samples were examined from pregnant animals between gestational days 1-8 using immunocytochemistry. The uterine luminal epithelium, the glandular epithelium, and the myometrial smooth muscle cells stained strongly from gestational days 1-8 with both nidogen antibodies. At day 4 the decidual reaction areas began to appear in the stromal matrix and immunostaining of both nidogens revealed that the basement membrane of the surface epithelium was discontinuous. The differentiation of stromal cells into decidual cells was seen at gestational day 5 and both nidogens were weakly expressed in the decidualizing cells. At day 6, nidogen-2 immunoreactivity was higher in the primary decidual cells close to the embryo than nidogen-1, and during development of the decidual tissue both nidogens appeared in the endometrial stromal cells. At day 7, while expression of both nidogens declined in the primary decidual cells, their expression was markedly observed in the secondary decidual cells close to the myometrium. At day 8, expression of both nidogens was also observed to increase in the primary decidual cells. While nidogen-2 expression was seen in the parietal endoderm and primary ectoderm of the rat embryos at this developmental stage, nidogen-1 expression was only detected in the parietal endoderm. These results indicate that nidogen-1 and nidogen-2 could play important roles during embryogenesis, decidualization, and implantation in the endometrium of rat uterus.

Inflammatory responses of corneal epithelial cells to Pseudomonas aeruginosa infection

PURPOSE

We hypothesized that corneal epithelium plays a role in the innate immune response by sensing the presence of pathogens and providing signals that activate the corneal defense system. We sought to determine the mechanisms involved in the activation of the signaling pathways and subsequent production of proinflammatory cytokines in human corneal epithelial cells (HCECs) in response to Pseudomonas aeruginosa infection.

METHODS

Epithelial monolayers of a telomerase-immortalized HCEC line, HUCL, and primary cultures of HCECs were exposed to P. aeruginosa (PA01 strain) with or without the presence of the NF-kappaB inhibitor kamebakaurin, the p38 inhibitor SB203580, or the JNK inhibitor SP600125. IkappaB-alpha phosphorylation and degradation and p38 and JNK phosphorylation were assessed at different time points by Western blot analysis. Interleukin (IL)-6, IL-8, and TNF-alpha levels were determined by reverse transcription-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA).

RESULTS

Exposure of HUCL cells and primary HCECs to P. aeruginosa resulted in rapid activation of NF-kappaB as indicated by an increase in IkappaB-alpha phosphorylation observed within 15 min and by IkappaB-alpha degradation, which peaked in 1 hr. Two stress-activated mitogen-activated protein kinases, p38 and JNK, were also activated as their phosphorylation was induced by P. aeruginosa infection. Concomitant with the activation of these Toll-like receptor-mediated signaling pathways, transcriptional expression and subsequent secretion of IL-6 and IL-8 in HUCL cells were also induced by P. aeruginosa. Presence of the NF-kappaB inhibitor kamebakaurin in culture medium blocked P. aeruginosa-induced NF-kappaB activation and inhibited IL-6, IL-8, and TNF-alpha expression and secretion. Inhibition of p38 or JNK also resulted in a decrease in bacteria-induced expression and secretion of these cytokines.

CONCLUSIONS

P. aeruginosa triggers an innate immune response in HCECs, and NF-kappaB and, to a lesser extent, the p38/JNK signal pathways are responsible for P. aeruginosa-induced proinflammatory cytokine production in these cells.

Blastocysts don't go it alone. Extrinsic signals fine-tune the intrinsic developmental program of trophoblast cells

The preimplantation embryo floats freely within the oviduct and is capable of developing into a blastocyst independently of the maternal reproductive tract. While establishment of the trophoblast lineage is dependent on expression of developmental regulatory genes, further differentiation leading to blastocyst implantation in the uterus requires external cues emanating from the microenvironment. Recent studies suggest that trophoblast differentiation requires intracellular signaling initiated by uterine-derived growth factors and integrin-binding components of the extracellular matrix. The progression of trophoblast development from the early blastocyst stage through the onset of implantation appears to be largely independent of new gene expression. Instead, extrinsic signals direct the sequential trafficking of cell surface receptors to orchestrate the developmental program that initiates blastocyst implantation. The dependence on external cues could coordinate embryonic activities with the developing uterine endometrium. Biochemical events that regulate trophoblast adhesion to fibronectin are presented to illustrate a developmental strategy employed by the peri-implantation blastocyst.

Molecular cues to implantation

Successful implantation is the result of reciprocal interactions between the implantation-competent blastocyst and receptive uterus. Although various cellular aspects and molecular pathways of this dialogue have been identified, a comprehensive understanding of the implantation process is still missing. The receptive state of the uterus, which lasts for a limited period, is defined as the time when the uterine environment is conducive to blastocyst acceptance and implantation. A better understanding of the molecular signals that regulate uterine receptivity and implantation competency of the blastocyst is of clinical relevance because unraveling the nature of these signals may lead to strategies to correct implantation failure and improve pregnancy rates. Gene expression studies and genetically engineered mouse models have provided valuable clues to the implantation process with respect to specific growth factors, cytokines, lipid mediators, adhesion molecules, and transcription factors. However, a staggering amount of information from microarray experiments is also being generated at a rapid pace. If properly annotated and explored, this information will expand our knowledge regarding yet-to-be-identified unique, complementary, and/or redundant molecular pathways in implantation. It is hoped that the forthcoming information will generate new ideas and concepts for a process that is essential for maintaining procreation and solving major reproductive health issues in women.

α5β1, αVβ3 and the platelet-associated integrin αIIbβ3 coordinately regulate adhesion and migration of differentiating mouse trophoblast cells

During blastocyst implantation, interaction between integrins on the apical surface of the trophoblast and extracellular matrix (ECM) in the endometrium anchors the embryo to the uterine wall. Strong adhesion of the blastocyst to fibronectin (FN) requires integrin signaling initiated by exogenous fibronectin. However, it is not known how integrin signaling enhances blastocyst adhesion. We present new evidence that the integrin, alphaIIbbeta3, plays a key role in trophoblast adhesion to fibronectin during mouse peri-implantation development. Trafficking of alphaIIb to the apical surface of the trophoblast increased dramatically after blastocysts were exposed to fibronectin, whereas other fibronectin-binding integrins, alpha5beta1 and alphaVbeta3, were resident at the apical surface before ligand exposure. Functional comparisons among the three integrins revealed that ligation of alpha5beta1 most efficiently strengthened blastocyst fibronectin-binding activity, while subsequent trophoblast cell migration was dependent primarily on the beta3-class integrins. In vivo, alphaIIb was highly expressed by invasive trophoblast cells in the ectoplacental cone and trophoblast giant cells of the parietal yolk sac. These data demonstrate that trafficking of alphaIIb regulates adhesion between trophoblast cells and fibronectin as invasion of the endometrium commences.

Adhesion, migration, transcriptional, interferon-inducible, and other signaling molecules newly implicated in cancer susceptibility and resistance of JB6 cells by cDNA microarray analyses

Relative expression levels of 9500 genes were determined by cDNA microarray analyses in mouse skin JB6 cells susceptible (P+) and resistant (P-) to 12-O-tetradecanoyl phorbol-13 acetate (TPA)-induced neoplastic transformation. Seventy-four genes in 6 functional classes were differentially expressed: (I) extracellular matrix (ECM) and basement membrane (BM) proteins (20 genes). P+ cells express higher levels than P- cells of several collagens and proteases, and lower levels of protease inhibitors. Multiple genes encoding adhesion molecules are expressed preferentially in P- cells, including six genes implicated in axon guidance and adhesion. (II) Cytoskeletal proteins (13 genes). These include actin isoforms and regulatory proteins, almost all preferentially expressed in P- cells. (III) Signal transduction proteins (12 genes). Among these are Ras-GTPase activating protein (Ras-GAP), the deleted in oral cancer-1 and SLIT2 tumor suppressors, and connexin 43 (Cx43) gap junctional protein, all expressed preferentially in P- cells. (IV) Interferon-inducible proteins (3 genes). These include interferon-inducible protein (IFI)-16, an Sp1 transcriptional regulator expressed preferentially in P- cells. (V) Other transcription factors (4 genes). Paired related homeobox gene 2 (Prx2)/S8 homeobox, and retinoic acid (RA)-regulated nur77 and cellular retinoic acid-binding protein II (CRABPII) transcription factors are expressed preferentially in P- cells. The RIN-ZF Sp-transcriptional suppressor exhibits preferential P+ expression. (VI) Genes of unknown functions (22 sequences). Numerous mesenchymal markers are expressed in both cell types. Data for multiple genes were confirmed by real-time PCR. Overall, 26 genes were newly implicated in cancer. Detailed analyses of the functions of the genes and their interrelationships provided converging evidence for their possible roles in implementing genetic programs mediating cancer susceptibility and resistance. These results, in conjunction with cell wounding and phalloidin staining data, indicated that concerted genetic programs were implemented that were conducive to cell adhesion and tumor suppression in P- cells and that favored matrix turnover, cell motility, and abrogation of tumor suppression in P+ cells. Such genetic programs may in part be orchestrated by Sp-, RA-, and Hox-transcriptional regulatory pathways implicated in this study.

Integrin signaling regulates blastocyst adhesion to fibronectin at implantation: intracellular calcium transients and vesicle trafficking in primary trophoblast cells

Accumulating evidence indicates that the endometrial extracellular matrix (ECM) modulates trophoblast adhesion during mouse blastocyst implantation. In previous studies of adhesion-competent mouse blastocysts, we have demonstrated that integrin-mediated fibronectin (FN)-binding activity on the apical surface of trophoblast cells is initially low, but becomes strengthened after embryos are exposed to FN. In the present study, we have examined whether the ligand-induced upregulation of trophoblast adhesion to FN is mediated by integrin signaling. The strengthening of adhesion to FN required integrin ligation, which rapidly elevated cytoplasmic-free Ca(2+). Chelation of intracellular Ca(2+) using BAPTA-AM, or inhibition of the Ca(2+)-dependent proteins, protein kinase C or calmodulin, significantly attenuated the effect of FN on binding activity. Furthermore, direct elevation of cytoplasmic Ca(2+) levels with ionomycin upregulated FN-binding activity, demonstrating that Ca(2+) signaling is required and sufficient for strong adhesion to FN. Ca(2+) signaling may induce protein trafficking, a known requirement for ligand-induced upregulation of FN-binding activity. Indeed, intracellular vesicles accumulated in adhesion-competent blastocysts, but were absent after exposure to either FN or ionomycin. These findings suggest that, during implantation, contact between peri-implantation blastocysts and FN elevates intracellular Ca(2+), which strengthens trophoblast adhesion to ECM through protein redistribution.

Molecules in blastocyst implantation: uterine and embryonic perspectives

Synchronized development of the embryo to the active stage of the blastocyst, differentiation of the uterus to the receptive state, and a "cross talk" between the blastocyst and uterine luminal epithelium are essential to the process of implantation. In spite of considerable accumulation of information and the present state of the knowledge, our understanding of the definitive mechanisms that regulate these events remains elusive. Although there are species variations in the process of implantation, many basic similarities do exist among various species. This review focuses on specific aspects of the implantation process in mice with the hope that many of the findings will be relevant to the process in humans. To establish signaling mechanisms of embryo-uterine interactions during implantation, studies on both embryonic and uterine consequences are required to generate more meaningful information. Due to ethical restriction and experimental limitation, it is difficult to generate such information in humans. This review has attempted to provide a comprehensive, but not complete, narration of a number of embryonic and uterine factors that are involved in the process of implantation in autocrine, paracrine, and/or juxtacrine manners in mice at the physiological, cellular, molecular, and genetic levels.

Nidogen is nonessential and not required for normal type IV collagen localization in Caenorhabditis elegans

Nidogen (entactin) can form a ternary complex with type IV collagen and laminin and is thought to play a critical role in basement membrane assembly. We show that the Caenorhabditis elegans nidogen homologue nid-1 generates three isoforms that differ in numbers of rod domain endothelial growth factor repeats and are differentially expressed during development. NID-1 appears at the start of embryonic morphogenesis associated with muscle cells and subsequently accumulates on pharyngeal, intestinal, and gonad primordia. In larvae and adults NID-1 is detected in most basement membranes but accumulates most strongly around the nerve ring and developing gonad. NID-1 is concentrated under dense bodies, at the edges of muscle quadrants, and on the sublateral nerves that run under muscles. Two deletions in nid-1 were isolated: cg119 is a molecular null, whereas cg118 produces truncated NID-1 missing the G2 collagen IV binding domain. Neither deletion causes overt abnormal phenotypes, except for mildly reduced fecundity. Truncated cg118 NID-1 shows wild-type localization, demonstrating that the G2 domain is not necessary for nidogen assembly. Both nid-1 mutants assemble type IV collagen in a completely wild-type pattern, demonstrating that nidogen is not essential for type IV collagen assembly into basement membranes.

Still more complexity in mammalian basement membranes

At the epithelial/mesenchymal interface of most tissues lies the basement membrane (BM). These thin sheets of highly specialized extracellular matrix vary in composition in a tissue-specific manner, and during development and repair. For about two decades it has been apparent that all BMs contain laminins, entactin-1/nidogen-1, Type IV collagen, and proteoglycans. However, within the past few years this complexity has increased as new components are described. The entactin/nidogen (E/N) family has expanded with the recent description of a new isoform, E/N-2/osteonidogen. Agrin and Type XVIII collagen have been reclassified as heparan sulfate proteoglycans (HSPGs), expanding the repertoire of HSPGs in the BM. The laminin family has become more diverse as new alpha-chains have been characterized, increasing the number of laminin isoforms. Interactions between BM components are now appreciated to be regulated through multiple, mostly domain-specific mechanisms. Understanding the functions of individual BM components and their assembly into macromolecular complexes is a considerable challenge that may increase as further BM and cell surface ligands are discovered for these proteins.

Integrin trafficking regulates adhesion to fibronectin during differentiation of mouse peri-implantation blastocysts

Trophoblast cells of the peri-implantation blastocyst differentiate from a polarized epithelium, the trophectoderm, into invasive cells having an apical surface occupied by integrins that mediate adhesion to the extracellular matrix. Blastocyst differentiation was assessed during serum-free culture using a fibronectin binding assay with intact mouse blastocysts. Fibronectin binding activity became elevated during a 24-h "window" after approximately 72 h of culture. Blastocyst differentiation was unaffected by transcriptional inhibition with alpha-amanitin, however, exposure of cavitating morulae to the drug significantly delayed the onset of maximal fibronectin-binding activity. Inhibition of de novo protein synthesis with cycloheximide delayed development only when added during the first 24 h of blastocyst culture, indicating that proteins required for adhesion to fibronectin were synthesized at least 24 h before blastocyst differentiation was completed. Since blastocyst differentiation did not appear to be regulated temporally by gene expression, the possible role of protein trafficking was investigated using the inhibitor, brefeldin A. Brefeldin A caused a reversible, dose-dependent decrease in fibronectin-binding activity when added to the culture medium between 48 and 72 h of culture. During the period of brefeldin A sensitivity, alpha 5 beta 1 integrin, a major fibronectin receptor, translocated to the apical surface of trophoblast cells, as determined by immunohistochemistry and confocal microscopy. Mouse blastocysts expressed other integrins that recognize the central cell-binding domain of fibronectin, including the alpha v integrins and alpha llb beta 3, but not alpha4 which recognizes the lllCS site. Trafficking of alpha 5 beta 1, and possibly other integrins, to the apical surface of trophoblast cells appears to be a critical step in the differentiation of the mouse blastocyst to an invasive phenotype.

Positioning of longitudinal nerves in C. elegans by nidogen

Basement membranes can help determine pathways of migrating axons. Although members of the nidogen (entactin) protein family are structural components of basement membranes, we find that nidogen is not required for basement membrane assembly in the nematode Caenorhabditis elegans. Nidogen is localized to body wall basement membranes and is required to direct longitudinal nerves dorsoventrally and to direct axons at the midlines. By examining migration of a single axon in vivo, we show that nidogen is required for the axon to switch from circumferential to longitudinal migration. Specialized basement membranes may thus regulate nerve position.

Mesenchymal entactin-1 (nidogen-1) is required for adhesion of peritubular cells of the rat testis in vitro

Epithelial-like Sertoli cells isolated from immature rat testis aggregate to form tubule-like structures when cultured on a monolayer of mesenchyme-derived peritubular cells. At the end of this morphogenetic process both cell types are separated by a basement membrane. In this study the gene expression of monocultures and direct cocultures of peritubular cells and Sertoli cells was examined using DD-RT-PCR. One of the isolated cDNA clones showed high homology to the cDNA encoding the basement membrane component entactin-1 (nidogen-1). Even though the entactin-1 (nidogen-1) gene is transcribed in peritubular cells, Sertoli cells, and in direct cocultures, the mRNA is translated only by the peritubular cells. No entactin-1 (nidogen-1) was detected in the Sertoli cells by Western blotting. Moreover, peritubular cell monocultures and cocultures showed the presence of one single band at 152 kDa in the supernatant, whereas in cell lysates two bands were detectable at 152 kDa and 150 kDa. Perturbation experiments using monoclonal antibodies directed against entactin-1 (nidogen-1) were performed with peritubular cells and Sertoli cells, respectively, and demonstrated loss of cell adhesion of the peritubular cells, while the Sertoli cells remained adherent. From these data we conclude that entactin-1 is exclusively produced and secreted by mesenchymal peritubular cells, and affects adhesion of peritubular cells in an autocrine manner.

Both adhesion to immobilized vitronectin and FcepsilonRI cross-linking cause enhanced focal adhesion kinase phosphorylation in murine mast cells

Murine mast cells adhere spontaneously to plate-bound vitronectin (VNPB) via alphav-containing integrins, and this adhesive interaction results in an augmented interleukin-3 (IL-3)-dependent mast-cell proliferation. In this report we demonstrate that the activation of murine mast cells through alphav-integrin, as well as through the high affinity immunoglobulin E (IgE) receptor (FcepsilonRI), results in enhanced tyrosine phosphorylation of focal adhesion kinase (FAK), a cytoplasmic protein tyrosine kinase involved in mitogenic and oncogenic signal transduction. While mast cell adhesion to VNPB resulted in enhanced FAK phosphorylation, treatment with soluble vitronectin (VNSOL) failed to do so. Spontaneous mast cell adhesion to entactin (EN) did not induce tyrosine phosphorylation of FAK, demonstrating that not all adhesive interactions lead to the same sequence of biochemical events. Because FAK has intrinsic tyrosine kinase activity, we examined whether activating mast cells via alphav-integrins, or via FcepsilonRI-cross-linking stimulated the in vitro kinase activity of FAK. Both pathways were found independently to activate FAK in mast cells and together appeared additive. Protein kinase C depletion in mast cells and calcium depletion in the medium caused decreased tyrosine phosphorylation of FAK, indicating that optimal tyrosine phosphorylation of FAK is regulated by both pathways. These data are consistent with the conclusion that the tyrosine phosphorylation of FAK represents at least one example of a point of convergence in the intracellular tyrosine phosphorylation cascades induced by alphav integrin-and FcepsilonRI-mediated signal transduction pathways in mast cells.

Renal cell carcinomas and pancreatic adenocarcinomas produce nidogen in vitro and in vivo

The production of nidogen by four renal cell carcinoma (RCC) and three pancreatic adenocarcinoma (PAc) cell lines has been studied in cell culture and in xenografted tumours in nude mice. In RCC cells, immunoreactivity for nidogen was seen only after exposure to monensin to induce cytoplasmic accumulation of secretory proteins. In PAc cells, immunoreaction was also detectable in control cells. Immunoblotting of control and monensin-exposed cells and immunoprecipitation of culture media of radioactively labelled cells demonstrated the production of nidogen polypeptide of Mr ca. 150000 by six of the seven cell lines. Basement membranes (BMs) and stroma of the xenografted tumours derived from these six cell lines demonstrated immunoreactivity for both human and mouse nidogen, as revealed with species-specific antibodies. The ability of the cells to produce nidogen in vitro and deposit in vivo was positively correlated with high histological grade of the xenografted tumours, although the small number of cell lines studied calls for further studies to confirm this. The distribution of nidogen in human RCC and PAc specimens was also studied by immunohistochemistry. There was strong immunoreactivity for nidogen in tumour stroma, BM of carcinoma cell nests, and endothelial basal lamina, but no conclusions could be drawn regarding histological grade and immunostaining patterns, because stromal production could not be ruled out. The results show that nidogen is produced by human carcinoma cells both in vitro and in vivo.

Nidogen-2: a new basement membrane protein with diverse binding properties

Human nidogen-2 was cloned and sequenced (1375 residues) and found to share 46% sequence identity and a similar domain arrangement with the previously characterized basement membrane protein nidogen-1. Recombinant nidogen-2 was purified as a 200 kDa protein from transfected mammalian cell medium, showed a high level of N and O-glycosylation, and could be clearly distinguished from nidogen-1 (150 kDa) by specific antibodies. Electron microscopy demonstrated that the two isoforms have a similar shape, consisting of three globular domains connected by two threads, but differ somewhat in length. Northern blots and immunological assays demonstrated co-expression of the nidogens in various tissues and cultured cells. Immunofluoresence revealed colocalization in vessel walls and other basement membrane zones but some differences in heart and skeletal muscle. Nidogen-2 interacted with collagens I and IV, and perlecan at a comparable level to nidogen-1 but failed to bind to fibulins. Nidogen-2 bound to laminin-1, but only moderately to the epitope on the laminin gamma1 chain, which promotes high-affinity binding of nidogen-1. Both nidogens were cell-adhesive for a restricted number of cell lines, with nidogen-2 having a higher activity. Together, these data suggest that nidogen-2 can compensate for some but not all functional activities ascribed to nidogen-1.

Entactin-2: a new member of basement membrane protein with high homology to entactin/nidogen

Using the new signal sequence trap (SST) method, we isolated several clones encoding secreted and transmembrane proteins from KUSA cells, a murine osteoblast-like cell line. One isolated novel clone, termed entactin-2, exhibited a high similarity to mouse entactin/nidogen, a basement membrane protein. Although deduction of the amino acid sequence of entactin-2 revealed only 27.4% homology to entactin, many structural similarities were seen between both proteins. Entactin-2 contains five EGF-like and two thyroglobulin-like motifs, which are both cysteine-rich. Comparison of both proteins clearly revealed that entactin-2 also contains related domain structures. The rod-like domain of entactin-2, containing the RGD integrin recognition sequence, fused to glutathione-S transferase (GST), revealed a cell surface-binding activity similar to that of entactin. In addition, the tissue distribution of entactin-2 mRNA resembled that of entactin. Furthermore, mRNA expression of both genes decreased as osteoblastic differentiation progressed. These results suggest that entactin-2 is a member of the entactin gene family, may have entactin-related functions, and might act as a basement membrane component.

Adhesion of cultured human kidney mesangial cells to native entactin: role of integrin receptors

Entactin is an extracellular matrix glycoprotein which binds to laminin and is found in most renal basement membranes and in the glomerular mesangial matrix. In the present study, we have characterized specific integrin receptors on cultured human mesangial cells (CHMC) responsible for adhesion to native entactin. The integrin receptors alpha 2 beta 1, alpha 3 beta 1, alpha 5 beta 1, alpha v beta 3, alpha v beta 5, and alpha 6 complexed with either beta 1 or beta 4 could be immune precipitated from detergent extracts of metabolically labeled CHMC. Adhesion assays with inhibitory anti integrin monoclonal antibodies (mab) demonstrated that CHMC use both alpha v beta 3 and a beta 1-containing integrin to bind surfaces coated with native entactin. Optimal binding of CHMC to native entactin required the participation of cations. Using wild type and mutant recombinant entactin fragments, the binding site for the alpha v beta 3 receptor was localized to the RGD sequence on the rod or E domain of entactin. CHMC adhesion to mutant full length recombinant entactin ligands lacking the E domain RGD sequence confirmed the presence of ligand binding site(s) for beta 1 integrin receptor(s). Differences in CHMC binding characteristics to recombinant and full length entactin compared to native bovine basement membrane entactin were observed. This suggests that tertiary molecular structure may contribute to entactin ligand binding properties. Primary amino acid residue sequences and tertiary structure of entactin may play roles in forming functional cell attachment sites in native basement membrane entactin.

Expression of smooth-muscle actin in cultured cells from human plasmacytoid myoepithelioma

OBJECTIVE

The definition of plasmacytoid myoepithelioma, a neoplasm exhibiting myoepithelial differentiation, has been recently questioned. To better understand the histogenesis of this neoplasm, we searched for myoepithelial markers in histologic sections of plasmacytoid myoepithelioma and in a cell line (M1) derived from this same neoplasm.

STUDY DESIGN

Expression of vimentin, pan-keratin (AE-3) and smooth-muscle actin was studied by immunohistochemistry in paraffin-embedded tissue and by immunofluorescence in M1 cells.

RESULTS

Plasmacytoid myoepithelioma tumor sections showed vimentin and AE-3 reactivity, but evidence of smooth-muscle actin was not seen. The cell line derived from this tumor also produced vimentin and cytokeratin. In addition, all cultured cells expressed smooth-muscle actin.

CONCLUSION

We demonstrated that cells derived from a case of plasmacytoid myoepithelioma appear to show full myoepithelial differentiation in vitro. Thus, they are myoepithelial-like cells in nature. The lack of myogenous differentiation in vivo could be due to an inhibitory process mediated by the extracellular matrix.

The alpha7beta1 integrin mediates adhesion and migration of skeletal myoblasts on laminin

Many aspects of myogenesis are believed to be regulated by myoblast interactions with specific components of the extracellular matrix. For example, laminin has been found to promote adhesion, migration, and proliferation of mammalian myoblasts. Based on affinity chromatography, the alpha7beta1 integrin has been presumed to be the major receptor mediating myoblast interactions with laminin. We have prepared a monoclonal antibody, O26, that specifically reacts with both the X1 and the X2 extracellular splice variants of the alpha7 integrin chain. This antibody completely and selectively blocks adhesion and migration of rat L8E63 myoblasts on laminin-1, but not on fibronectin. In contrast, a polyclonal antibody to the fibronectin receptor, alpha5beta1 integrin, blocks myoblast adhesion on fibronectin, but not on laminin-1. The alpha7beta1 integrin also binds to a mixture of laminin-2 and laminin-4, the major laminin isoforms in developing and adult skeletal muscle, but O26 is a much less potent inhibitor of myoblast adhesion on the laminin-2/4 mixture than on laminin-1. Based on affinity chromatography, we suggest that this may be due to higher affinity binding of alpha7X1 to laminin-2/4 than to laminin-1.

Integrins and reproductive physiology: expression and modulation in fertilization, embryogenesis, and implantation

OBJECTIVE

To review the available information regarding the role of integrins in reproductive physiology and to discuss their potential clinical implications.

DESIGN

Studies that specifically relate to the expression and modulation of integrins in fertilization, embryogenesis, and implantation were identified through the literature and Medline searches.

RESULT(S)

Integrins are a class of adhesion molecules that participate in cell-to-cell and cell-to-substratum interactions and are present on essentially all human cells. All mammalian eggs express integrins at their surface, and the integrin alpha 6 beta 1 serves as a sperm receptor that mediates sperm-egg binding. In addition, certain integrin moieties appear to be regulated within the cycling endometrium. Specifically, the expression of beta 1 integrins in the early proliferative phase is restricted to the glandular epithelium, whereas stromal cells also express beta 1 integrins in the midsecretory phase. The expression of beta 1 integrins increases at the time of implantation and remains elevated in the decidua during early pregnancy. A disruption of integrin expression is associated with certain types of infertility in women. The apical surface of the mural trophectoderm does indeed possess functional integrins, and trophoblast interactions with extracellular matrix proteins largely depend on the integrin family of adhesion receptors.

CONCLUSION(S)

Integrins play particularly important roles in both fertilization and embryogenesis, including the process of implantation.

Human trophoblast cell adhesion to extracellular matrix protein, entactin

PROBLEM

Trophoblast interaction with endometrial extracellular matrix (ECM) is crucial during human embryo implantation and placentation. Entactin, a ubiquitous basement membrane glycoprotein, plays a central role in ECM assembly, cell attachment, and chemotaxis. The present study was conducted to examine the possible role of entactin in promoting human trophoblast adhesion.

METHODS

Using an extended life span first trimester trophoblast cell line HTR-8/SVneo (HTR) and a cell adhesion assay, we measured the adherence of human first trimester trophoblasts to recombinant entactin and its domains. Also, we used flow cytometry and indirect immunofluorescence to detect the presence of integrins that may be involved in human trophoblast-entactin interaction; these methods were used to analyze HTR cells, as well as tissue sections and freshly isolated human trophoblasts from first trimester and term placenta.

RESULTS

We found that first trimester trophoblast cells were highly adherent to entactin and its E and G2 domains but not to G1 or G3 domains. Using indirect immunofluorescence and flow cytometry, we found that both beta 1 and beta 3 integrin subunits were expressed on the surface of HTR trophoblast cells adhering to entactin; in contrast, beta 2 and beta 4 integrin subunits were not detected. In addition, we found that alpha v beta 3 was expressed on freshly isolated villous cytotrophoblasts and cytotrophoblast and syncytiotrophoblasts in tissue sections from term placenta. The beta 3 integrin subunit was expressed in cytotrophoblasts and syncytiotrophoblasts in villi of first trimester placental tissue sections.

CONCLUSION

Recombinant entactin promotes human trophoblast cell adhesion through both its E and G2 domains and these specific adhesive interactions may be mediated by beta 1 and/or beta 3 class integrins.

Entactin modulates the attachment of rabbit corneal epithelial cells

PURPOSE

To understand the biological activity of entactin, a component of the basement membrane of the corneal epithelium, we investigated the ability of rabbit corneal epithelial cells to attach to an entactin matrix and the effect of entactin on the cells' attachment to other corneal basement proteins.

METHODS

Multiwell plastic plates were coated with bovine serum albumin (BSA), alone or with BSA and entactin, laminin, fibronectin or collagen type IV. Cultured rabbit corneal epithelial cells were seeded on the plates. After incubation (usually 90 min), the cells were fixed and stained with 1% crystal violet. The number of attached cells was counted under a light microscope.

RESULTS

The numbers of attached cells increased in proportion to both the incubation period and the concentration of entactin coated. Furthermore, the number of cells attached to the entactin-coated plate was greater than the number attached to the BSA-coated plate for each incubation period (30 to 120 min). Likewise, when laminin-coated plates were treated with entactin, the number of the attached cells increased in proportion to the concentration of entactin. However, entactin did not affect the cellular attachment of fibronectin or type IV collagen. Cellular attachment to entactin was partially inhibited by the cells' preincubation with the synthetic peptide (GRGDSP).

CONCLUSIONS

The present results showed that cultured corneal epithelial cells adhere to entactin and that entactin stimulated the attachment of these cells to the laminin matrix. These findings suggest that entactin plays a specific role in maintaining the normal integrity of the corneal epithelium.

Role of laminin-nidogen complexes in basement membrane formation during embryonic development

Laminin and nidogen (entactin) are major glycoprotein components of basement membranes. At least seven different isoforms of laminin have been identified. Laminin and nidogen form high affinity complexes in basement membranes by specific binding between the laminin gamma 1 chain and the G3 globule of nidogen. Additional interactions between nidogen and collagen IV, perlecan and other basement membrane components result in the formation of ternary complexes between these matrix components. Nidogen is highly susceptible to proteolytic cleavage, and binding to laminin protects nidogen from degradation. Nidogen is considered to have a crucial role as a link protein in the assembly of basement membranes. Basement membrane components are synthesized at high levels during tissue growth and development, and sites of morphogenesis correlate with localized remodelling of basement membranes. The formation of distinct basement membrane matrices in the developing embryo is influenced by the laminin isoforms produced and by whether laminin and nidogen are co-expressed and secreted as a complex or are produced by cooperation between two cell layers. The potential roles of laminin-nidogen complexes, cell-matrix interactions, and other intermolecular interactions within the matrix in basement membrane assembly and stability are discussed in this review.

Molecular interactions between fibronectin and integrins during mouse blastocyst outgrowth

To investigate the mechanism of trophoblast adhesion to fibronectin, we cultured blastocysts in serum-free medium on proteolytic fibronectin fragments containing its major functional domains, and localized fibronectin-binding integrins in outgrowing trophoblast cells by immunofluorescent staining. Outgrowth comparable to that obtained with intact fibronectin was observed using a 120 kD chymotryptic fragment containing the central cell-binding domain (FN-120) and the Arg-Gly-Asp (RGD) recognition sequence. A 40 kD COOH-terminal chymotryptic fragment of fibronectin containing both a heparin-binding region and an alternate (non-RGD) cell-binding site was inactive in supporting trophoblast adhesion. Three synthetic peptides derived from the heparin-binding domain, including the CS1 alternate cell-binding site, were also unable to promote trophoblast cell adhesion. A 75 kD recombinant protein, ProNectin F, containing 13 copies of the cell recognition epitope of fibronectin, Val-Thr-Gly-Arg-Gly-Asp-Ser-Pro-Ala-Ser, vigorously supported blastocyst outgrowth. Blastocyst outgrowth was not significantly different when surfaces were precoated with cellular fibronectin, which contains an alternatively spliced type III repeat and is the form actually encountered in vivo. Several putative fibronectin receptors were localized in trophoblast outgrowths by immunofluorescent labeling. Antibodies reactive with integrin subunits alpha 3, alpha 5, alpha IIb, alpha v, beta 1 and beta 3, but not alpha 4, all bound to trophoblast cells. Antibodies raised against either the beta 1 or beta 3 integrin subunits significantly inhibited fibronectin-mediated outgrowth. These findings demonstrate the key role of the central cell-binding domain of fibronectin in trophoblast adhesion, and suggest four RGD-binding integrins, alpha 3 beta 1, alpha 5 beta 1, alpha IIb beta 3, and alpha v beta 3, that could mediate trophoblast adhesion in vitro and may play an important role during implantation.