Biomedical subjects

D Randall Armant

Publications and source records attributed to D Randall Armant.

18 recordsLinked to original sources

PubMed2006

Trophoblast adhesion of the peri-implantation mouse blastocyst is regulated by integrin signaling that targets phospholipase C.

Integrin signaling modulates trophoblast adhesion to extracellular matrices during blastocyst implantation. Fibronectin (FN)-binding activity on the apical surface of trophoblast cells is strengthened after elevation of intracellular Ca(2+) downstream of integrin ligation by FN. We report here that phosphoinositide-specific phospholipase C (PLC) mediates Ca(2+) signaling in response to FN. Pharmacological agents used to antagonize PLC (U73122) or the inositol phosphate receptor (Xestospongin C) inhibited FN-induced elevation of intracellular Ca(2+) and prevented the upregulation of FN-binding activity. In contrast, inhibitors of Ca(2+) influx through either voltage-gated or non-voltage-gated Ca(2+) channels were without effect. Inhibition of protein tyrosine kinase activity by genistein, but not G-protein inhibition by suramin, blocked FN-induced intracellular Ca(2+) signaling and upregulation of adhesion, consistent with involvement of PLC-gamma. Confocal immunofluorescence imaging of peri-implantation blastocysts demonstrated that PLC-gamma2, but not PLC-gamma1 nor PLC-beta1, accumulated near the outer surface of the embryo. Phosphotyrosine site-directed antibodies revealed phosphorylation of PLC-gamma2, but not PLC-gamma1, upon integrin ligation by FN. These data suggest that integrin-mediated activation of PLC-gamma to initiate phosphoinositide signaling and intracellular Ca(2+) mobilization is required for blastocyst adhesion to FN. Signaling cascades regulating PLC-gamma could, therefore, control a critical feature of trophoblast differentiation during peri-implantation development.

Animals↗

PubMed2006

Human trophoblast survival at low oxygen concentrations requires metalloproteinase-mediated shedding of heparin-binding EGF-like growth factor.

Heparin-binding EGF-like growth factor (HBEGF), which is expressed in the placenta during normal pregnancy, is down regulated in pre-eclampsia, a human pregnancy disorder associated with poor trophoblast differentiation and survival. This growth factor protects against apoptosis during stress, suggesting a role in trophoblast survival in the relatively low O(2) ( approximately 2%) environment of the first trimester conceptus. Using a well-characterized human first trimester cytotrophoblast cell line, we found that a 4-hour exposure to 2% O(2) upregulates HBEGF synthesis and secretion independently of an increase in its mRNA. Five other expressed members of the EGF family are largely unaffected. At 2% O(2), signaling via HER1 or HER4, known HBEGF receptors, is required for both HBEGF upregulation and protection against apoptosis. This positive-feedback loop is dependent on metalloproteinase-mediated cleavage and shedding of the HBEGF ectodomain. The restoration of trophoblast survival by the addition of soluble HBEGF in cultures exposed to low O(2) and metalloproteinase inhibitor suggests that the effects of HBEGF are mediated by autocrine/paracrine, rather than juxtacrine, signaling. Our results provide evidence that a post-transcriptional mechanism induced in trophoblasts by low O(2) rapidly amplifies HBEGF signaling to inhibit apoptosis. These findings have a high clinical significance, as the downregulation of HBEGF in pre-eclampsia is likely to be a contributing factor leading to the demise of trophoblasts.

Apoptosis↗

PubMed2006

Rapid induction of apoptosis in gastrulating mouse embryos by ethanol and its prevention by HB-EGF.

BACKGROUND: Ethanol exposure during gastrulation and early neurulation induces apoptosis within certain embryonic cell populations, leading to craniofacial and neurological defects. There is currently little information about the initial kinetics of ethanol-induced apoptosis, and interest in the ability of endogenous survival factors to moderate apoptosis is growing. Ethanol alters intracellular signaling, leading to cell death in chick embryos, suggesting that apoptosis could occur rapidly and that signaling pathways activated by survival factors might reduce apoptosis. METHODS: Pregnant mice were intubated with 1, 2, or 4 g/kg ethanol on day 7.5 of embryogenesis (E7.5) 1, 3, or 6, hours before harvesting gastrulation-stage embryos. Control animals received maltose/dextran. Blood alcohol concentrations (BAC) were determined by gas chromatography. E7.5 embryos isolated from untreated dams were cultured in vitro for 1 or 3 hr with 0 or 400 mg% ethanol and 0 or 5 nM heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF). Apoptosis was quantified using fluorescence microscopy to detect annexin V binding and DNA fragmentation [terminal deoxynucleotidyl transferase-mediated dUTP-X nick end labeling (TUNEL)] in whole-mount or sectioned embryos. RESULTS: Both annexin V binding and TUNEL were elevated (p < 0.05) in embryos exposed in utero to 1 g/kg ethanol for 3 hours, increasing linearly with time and ethanol concentration. Apoptosis increased (p < 0.05) in all germ cell layers. Mice treated with 4 g/kg sustained BAC of 400 mg% for nearly 3 hours, significantly increasing apoptosis within the first hour. Cultured embryos exposed to 400 mg% ethanol displayed 2- to 3-fold more TUNEL than vehicle-treated embryos (p < 0.05); however, exogenous HB-EGF prevented apoptosis. CONCLUSIONS: Ethanol rapidly produced apoptosis in gastrulation-stage embryos, consistent with induction by intracellular signaling. The ethanol-induced apoptotic pathway was blocked by the endogenous survival factor, HB-EGF. Differences in the expression of survival factors within individual embryos could be partly responsible for variations in the teratogenic effects of ethanol among offspring exposed prenatally.

Animals↗

PubMed2006

Blastocyst culture.

Experimental models of blastocyst development based on in vitro culture have played a prominent role in advancing our understanding of peri-implantation development, a process that is relatively inaccessible in vivo. Blastocyst culture provides a robust approach for examining embryonic interactions with the microenvironment under highly controlled conditions. Major events that occur in utero can be followed in vitro, including blastocyst expansion, hatching, and adhesion to extracellular matrices. This chapter will describe a method for obtaining and culturing mouse blastocysts. Morphological changes that occur during blastocyst culture will be discussed and related to the corresponding development in utero. Finally, quantitative assays will be detailed for monitoring peri-implanatation development of the trophoblast in vitro.

Animals↗

PubMed2005

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.

Animals↗

PubMed2005

Toll-like receptor 4: a potential link between "danger signals," the innate immune system, and preeclampsia?

OBJECTIVE: Toll-like receptors (TLRs) recognize microbial ligands and host products that are released during tissue damage, the so-called "danger signals." This study was conducted to determine whether changes in TLR-4 and TLR-2 expressions can be detected in the trophoblasts at the placental bed of women with and without preeclampsia. STUDY DESIGN: Placental bed biopsy specimens were obtained from women with: (1) normal term pregnancies with and without labor (each n = 20); (2) preeclampsia who delivered preterm (n = 15); and (3) preterm labor and intact membranes with and without chorioamnionitis (each n = 15). The expression pattern of TLR-4 and TLR-2 in the trophoblasts was analyzed by double immunohistochemistry. RESULTS: (1) The median percentage of TLR-4 positive interstitial trophoblasts was significantly higher in patients with preeclampsia than in patients with preterm labor without or with histologic chorioamnionitis (P = .0002 and P = .02, respectively). (2) The median percentage of TLR-2 positive interstitial trophoblasts was not different among the study groups (P>.05). (3) TLR-4 positive trophoblasts were also frequently immunoreactive to activated nuclear factor-kappaB, tumor necrosis factor-alpha, and M30 (a specific apoptosis antigen for trophoblast). (4) Lipopolysaccharide treatment inhibited the migration of trophoblast cell lines in vitro. CONCLUSION: TLR-4 protein expression is increased in interstitial trophoblasts of patients with preeclampsia. We propose that "danger signals" at the feto-maternal interface, which are recognized by trophoblasts through TLR-4, may play a key role in the creation of a local abnormal cytokine milieu. This suggests a novel mechanism that links the activation of the innate immune system through TLR-4 and preeclampsia.

Cell Movement↗

PubMed2005

Ethanol triggers neural crest apoptosis through the selective activation of a pertussis toxin-sensitive G protein and a phospholipase Cbeta-dependent Ca2+ transient.

BACKGROUND: Alcohol is a potent neurotoxin that triggers the selective apoptosis of neuronal populations in the developing fetus. For neural crest cells, clinically relevant ethanol levels (0.3%) rapidly elicit a phospholipase C (PLC)-dependent intracellular Ca2+ transient that is sufficient to activate apoptosis. We investigated the biochemical origins of this Ca2+ transient. METHODS: Three somite chick embryos (stage 8-) were pretreated with agonists and antagonists of PLC signaling pathways before ethanol challenge. The resulting intracellular Ca2+ release was quantified using Fluo-3; apoptosis was assessed using vital dyes. RESULTS: Pretreatment of embryos with PLC antagonists U73122 or ET-18-OCH3 confirmed that a phosphoinositide-specific PLC was required for both the ethanol-dependent Ca2+ transient and subsequent cell death. Ethanol rapidly elevated intracellular inositol-1,4,5-trisphosphate [Ins(1,4,5)P3] levels in the rostral portion of the embryo that contains neural crest progenitors. The Ins(1,4,5)P3 receptor antagonist xestospongin C blocked the appearance of the ethanol-dependent Ca2+ transient. Pretreatment with the pan-Galpha protein antagonist GDPbetaS, but not with the tyrosine kinase antagonist genistein, suppressed ethanol's ability to elicit the Ca2+ transient, suggesting that a rise in PLC activity and Ins(1,4,5)P3 concentration originates from stimulation of heterotrimeric G proteins. To probe the identity of this G protein, embryos were treated with G protein antagonists. Pertussis toxin and NF023 suppressed the ethanol-induced Ca2+ transient and subsequent neural crest apoptosis, whereas suramin was weakly inhibitory. C3 exoenzyme was embryolethal over a wide concentration range, consistent with suggestions that Rho family GTPases participate in neural crest development. Galphai2 was identified by immunostaining in the neural crest cells. CONCLUSION: We propose a role for Galphai/o protein activation and subsequent interaction of Gbetagamma with PLCbeta in mediating the proapoptotic effects of ethanol upon the developing neural crest.

Animals↗

PubMed2004

Lysophosphatidic acid regulates murine blastocyst development by transactivation of receptors for heparin-binding EGF-like growth factor.

Transient elevation of intracellular calcium (Ca2+(i)) by various means accelerates murine preimplantation development and trophoblast differentiation. Several G-protein-coupled receptors (GPCRs), including the lysophosphatidic acid (LPA) receptor (LPAR), induce Ca2+(i) transients and transactivate the EGF receptor (ErbB1) through mobilization of EGF family members, including heparin-binding EGF-like growth factor (HB-EGF). Because HB-EGF accelerates blastocyst differentiation in vitro, we examined whether crosstalk between LPA and HB-EGF regulates peri-implantation development. During mouse blastocyst differentiation, embryos expressed LPAR1 mRNA constitutively, LPAR2 only in late stage blastocysts and no LPAR3. Consistent with a mechanism based on Ca2+(i) signaling, LPA rapidly accelerated the rate of trophoblast outgrowth, an index of blastocyst differentiation, and chelation of Ca2+(i) with BAPTA-AM blocked LPA stimulation. Interfering with HB-EGF signaling through ErbB1 or ErbB4 also attenuated LPA stimulation. We established that mouse blastocysts indeed express HB-EGF and that LPA induces the transient accumulation of HB-EGF on the embryo surface, which was blocked by treatment with either BAPTA-AM or the protein trafficking inhibitor, brefeldin A. We conclude that LPA accelerates blastocyst differentiation through its ability to induce Ca2+(i) transients and HB-EGF autocrine signaling. Transactivation of ErbB1 or ErbB4 by HB-EGF could represent a convergent signaling pathway accessed in the trophoblast by stimuli that mobilize Ca2+(i).

Animals↗

PubMed2004

Alpha5beta1, alphaVbeta3 and the platelet-associated integrin alphaIIbbeta3 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.

Animals↗

PubMed2004

Heparin-binding EGF-like growth factor regulates human extravillous cytotrophoblast development during conversion to the invasive phenotype.

Cytotrophoblasts of the anchoring villi convert during human placentation from a transporting epithelium to an invasive, extravillous phenotype that expresses a distinct repertoire of adhesion molecules. Developing extravillous trophoblasts accumulate heparin-binding EGF-like growth factor (HB-EGF), a multifunctional cytokine, which binds HER1 and HER4 of the human EGF receptor (HER/ErbB) family. HB-EGF is downregulated in placentae of women with preeclampsia, a disorder associated with deficient trophoblast invasion, raising important questions about its physiological impact on cytotrophoblasts. Addition of HB-EGF during explant culture of first-trimester chorionic villi enhanced extravillous trophoblast differentiation and invasive activity. Using a first-trimester human cytotrophoblast line, the potential for autocrine and paracrine regulation of the developing trophoblast was established based on the expression of all four HER isoforms, as well as HB-EGF and related growth factors. HB-EGF did not alter proliferation, but initiated extravillous differentiation, with decreased alpha6 integrin expression, increased alpha1, and elevated cell migration. Function-blocking antibodies against EGF family members reduced basal cell motility and antibody inhibition of either HER1 or HER4 ligation prevented HB-EGF-induced integrin switching. We conclude that HER-mediated autocrine and paracrine signaling by HB-EGF or other EGF family members induces cytotrophoblast differentiation to an invasive phenotype.

Animals↗

PubMed2004

Histamine enhances cytotrophoblast invasion by inducing intracellular calcium transients through the histamine type-1 receptor.

Blastocyst implantation and placentation require molecular and cellular interactions between the uterine endometrium and blastocyst trophectoderm. Previous studies showed that histamine produced in the mouse uterine luminal epithelium interacts with trophoblast histamine type-2 receptors (H2) to initiate blastocyst implantation. However, it is unknown whether similar histamine activity is operative in humans. Using a human cell line (HTR-8/SVneo) derived from first-trimester cytotrophoblasts that expresses both histamine type-1 receptor (H1) and H2, we found that histamine promotes cytotrophoblast invasiveness specifically through activation of H1. Stimulation of H1 in human cytotrophoblasts by histamine induced intracellular Ca2+ (Ca(2+)i) transients by activating phospholipase C and the inositol trisphosphate pathway. The enhanced invasion induced by histamine was blocked by pretreatment with H1 antagonist or by chelation of Ca(2+)i. These findings suggest possible differences between rodents and humans in histamine signaling to the trophoblast.

Calcium↗

PubMed2003

Ethanol-induced cephalic apoptosis requires phospholipase C-dependent intracellular calcium signaling.

BACKGROUND: Although the ability of ethanol to elicit neural crest cell apoptosis is well documented, the initial target of ethanol in these cells, and the biochemical pathway leading to their apoptosis, have yet to be determined. Recent work in preimplantation mouse embryos demonstrates that ethanol induces a phospholipase-C (PLC)-dependent calcium transient that mediates ethanol's effects. We tested whether a similar effect on calcium and PLC is involved in ethanol-induced neural crest apoptosis. METHODS: Chicken embryos were collected and loaded with Fluo-3-AM to assess the effects of ethanol on intracellular calcium levels. Pharmacological agents were used to determine the sources and mechanism of intracellular calcium increases. In separate experiments, embryos were treated in ovo with pharmacological modulators of calcium signaling prior to ethanol exposure, and resulting levels of cell death were assessed by using the vital dye acridine orange. RESULTS: Ethanol exposure caused a localized increase in intracellular calcium levels in embryonic neural folds within 15 sec of ethanol exposure. Ethanol-induced apoptosis was specifically blocked by chelation of intracellular calcium before ethanol exposure. Pretreatment with the PLC inhibitor U73122 blocked ethanol-induced apoptosis as well as the intracellular calcium transient. Depletion of extracellular calcium resulted in a partial block of ethanol-induced apoptosis. CONCLUSIONS: Ethanol exposure alters calcium signaling within the neurulation-stage chicken embryo in a PLC-dependent manner. Increases in intracellular calcium and PLC activity are necessary for ethanol's induction of apoptosis within cephalic populations. These effects likely represent an early and crucial event in the pathway leading to ethanol-induced cell death.

Animals↗

PubMed2002

Pre-eclampsia and expression of heparin-binding EGF-like growth factor.

BACKGROUND: Pre-eclampsia is a disorder of pregnancy associated with poor extravillous cytotrophoblast invasion and above-normal rates of apoptosis in the trophoblast. Heparin-binding epidermal-growth-factor-like growth factor (HB-EGF) has strong cytoprotective activity and is an important signalling protein that regulates trophoblast invasion during early placentation. We aimed to establish whether HB-EGF expression is altered in placentae of pre-eclamptic women. METHODS: We assessed the expression of HB-EGF mRNA and protein by in-situ hybridisation and immunohistochemical techniques, respectively, in archived placental tissues from pregnancies terminated at around 20 weeks of gestation, and from women delivering between weeks 19 and 35 of gestation with preterm labour, small for gestational age infants, or pre-eclampsia. FINDINGS: HB-EGF mRNA and protein were expressed in villous and extravillous cytotrophoblast cells up to week 35 of gestation in placentae from women who delivered preterm. Similar levels of HB-EGF protein were found in the placentae of women who were not in labour. HB-EGF expression was reduced about five-fold (p=0.0001) in pre-eclamptic pregnancies. Fetal growth retardation, which has been linked with shallow trophoblast invasion and moderate apoptosis, was associated with placentae expressing intermediate levels of HB-EGF. INTERPRETATION: In pre-eclampsia, deficient HB-EGF signalling during placental development could impair trophoblast survival, differentiation, and invasion, leading to poor placental perfusion and hypertension.

Adult↗

PubMed2002

Calcitonin down-regulates E-cadherin expression in rodent uterine epithelium during implantation.

Previous studies indicated that calcitonin (CT), a peptide hormone involved in calcium homeostasis, is transiently expressed in the receptive rat and human endometrial epithelia within the window of implantation. Attenuation of uterine CT expression using antisense methods severely impaired implantation in the rat. The molecular pathway of CT in the pregnant uterus, however, remains unknown. In the present study, we investigated the cellular events following the binding of CT to its membrane receptors in human endometrial epithelial cell line Ishikawa. We observed that CT treatment triggers a transient rise in intracellular calcium in these cells. Most interestingly, CT treatment also led to the disappearance of E-cadherin, a critical cell adhesion molecule, from cell-cell contact sites. Blockade of intracellular calcium release by BAPTA-AM (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl) prevented the CT-induced disappearance of E-cadherin. Our studies further revealed that CT treatment markedly down-regulates the level of E-cadherin mRNA in Ishikawa cells. We also examined whether CT influences the expression of E-cadherin mRNA in intact rat uterine tissue during implantation. In pregnant rats, high levels of E-cadherin mRNA were expressed during the first 3 days of gestation when the CT mRNA in uterine epithelial cells is undetectable. Concomitant with a transient burst of CT expression during days 4-5 of pregnancy, the level of E-cadherin mRNA declined sharply. Furthermore, administration of exogenous CT to animals on day 2 of pregnancy led to a premature suppression of E-cadherin mRNA level on day 3, indicating a direct link between elevated levels of uterine CT and the down-regulation of E-cadherin expression in the surface epithelium. Collectively, our results are consistent with the hypothesis that CT-induced reduction in E-cadherin expression may remodel the adherens junctions between epithelial cells, and this change in epithelial cell phenotype might be a critical event during the implantation of the blastocyst.

Animals↗

PubMed2002

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.

Animals↗

PubMed2002

Identification, molecular characterization, and tissue expression of OVCOV1.

Key to the maternal-embryonic dialogue during early implantation are the extra embryonic trophoblast cells that play several critical roles including invasion of the maternal decidua. Cytotrophoblast proliferation and differentiation along an invasive pathway is regulated by a positive gradient of oxygen tension. We have employed transcript profiling to characterize the extra-embryonic tissues during early human implantation. We probed a cDNA library isolated from the ectoplacental cone region of stage 7.5 days post coitus mouse embryos with cDNA from hypoxic cultured human trophoblast cells. This identified the pattern of expression of a series of previously unknown genes that correlate to day 20 of human embryonic development. One EST was selected for further analysis since it is identical to the 1588-bp CGI-15 sequence assembled in silico. The human gene is organized into 10 exons 2063 bp in length. The open reading frame contains 1272 bp predicting protein composed of 365 amino acids. This gene is expressed in many tissues including those found in the reproductive tract. Its expression is regulated by oxygen tension and is unaffected by estradiol or progesterone treatment.

Animals↗

PubMed2002

Integrin-mediated adhesion and signaling during blastocyst implantation.

Blastocyst implantation in rodents and primates depends on adhesive interactions between trophoblast cells and the endometrial extracellular matrix. As the blastocyst contacts the uterine basal lamina, cells of the trophectoderm become adhesion-competent and conclude their phenotypic conversion from a polarized epithelium to invasive trophoblast cells that anchor the embryo in the uterine wall and eventually infiltrate the endometrium. Trophoblast cells become capable of adhesion to fibronectin as alpha(5)beta(1) integrins traffick to their apical surfaces. While integrin trafficking may be required for trophoblast adhesion to the endometrium, accumulating evidence indicates that, in response to contact with the extracellular matrix, additional molecules must be recruited to the apical surface before strong adhesion is attained. Based on the known interactions of integrins with cytoplasmic regulatory proteins, we propose that extracellular matrix-bound integrins mediate intracellular signaling cascades that strengthen their adhesive activity. We will review some of the known integrin signaling pathways that could regulate trophoblast adhesion and differentiation.

Animals↗

PubMedDate not supplied

Expression of genes for alcohol and aldehyde metabolizing enzymes in mouse oocytes and preimplantation embryos.

Alcohols and aldehydes are metabolized primarily by alcohol (ADH) and aldehyde (ALDH) dehydrogenase isozymes. Although significant progress has been made towards understanding the involvement of these isozymes in the oxidation of alcohol and aldehydes in the body, it is not known how these compounds are handled during fertilization and preimplantation embryogenesis. In this study, reverse transcription and the polymerase chain reaction (RT-PCR) was used to determine which ADH and ALDH isozymes are expressed at the oocyte, zygote, morula, and blastocyst stages of preimplantation development in the mouse. Transcripts of beta-actin and vimentin, assayed as controls, were detected at all stages, as well as Class III ADH (Adh-2) and Class 3 ALDH (Ahd-4), involved in the detoxification of formaldehyde and aromatic aldehydes, respectively. In contrast, transcripts for the major ethanol oxidizing isozyme, Class I ADH (Adh-1) was not detected during preimplantation development. Cytosolic retinol dehydrogenase (Adh-3) transcripts were marginally detected in oocytes and zygotes. The mRNA for cytosolic retinal dehydrogenase (Ahd-2), microsomal short-chain retinol dehydrogenases (RoDH Type I), and the mitochondrial low-Km acetaldehyde dehydrogenase (Ahd-5) only appeared as maternal transcripts. Microsomal ALDH (Ahd-3), which is induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), was not expressed until the blastocyst stage. ADH and ALDH enzyme systems may guard mouse preimplantation embryos against the toxic effects of industrial pollutants, such as formaldehyde and TCDD, as well as peroxidatic aldehydes generated during lipid peroxidation. The absence of enzymes to convert ethanol to acetaldehyde, coupled with oocyte expression of the acetaldehyde-degrading enzyme, Ahd-5, may be protective for the early embryo.

Actins↗