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At least 811 records · Page 45Linked to original sources
PubMed1999

Hrs, a FYVE finger protein localized to early endosomes, is implicated in vesicular traffic and required for ventral folding morphogenesis.

Hrs is an early endosomal protein homologous to Vps27p, a yeast protein required for vesicular trafficking. Hrs has a FYVE double zinc finger domain, which specifically binds phosphatidylinositol(3)-phosphate and is conserved in several proteins involved in vesicular traffic. To understand the physiological role of Hrs, we generated mice carrying a null mutation of the gene. Hrs homozygous mutant embryos developed with their ventral region outside of the yolk sac, had two independent bilateral heart tubes (cardia bifida), lacked a foregut, and died around embryonic day 11 (E11). These phenotypes arise from a defect in ventral folding morphogenesis that occurs normally around E8.0. Significant apoptosis was detected in the ventral region of mutant embryos within the definitive endoderm, suggesting an important role of this germ layer in ventral folding morphogenesis. Abnormally enlarged early endosomes were detected in the mutants in several tissues including definitive endoderm, suggesting that a deficiency in vesicular transport via early endosomes underlies the mutant phenotype. The vesicular localization of Hrs was disrupted in cells treated with wortmannin, implicating Hrs in the phosphatidylinositol 3-kinase pathway of membrane trafficking.

Androstadienes↗
PubMed2006

Cyclooxygenase-1-derived PGE2 promotes cell motility via the G-protein-coupled EP4 receptor during vertebrate gastrulation.

Gastrulation is a fundamental process during embryogenesis that shapes proper body architecture and establishes three germ layers through coordinated cellular actions of proliferation, fate specification, and movement. Although many molecular pathways involved in the specification of cell fate and polarity during vertebrate gastrulation have been identified, little is known of the signaling that imparts cell motility. Here we show that prostaglandin E(2) (PGE(2)) production by microsomal PGE(2) synthase (Ptges) is essential for gastrulation movements in zebrafish. Furthermore, PGE(2) signaling regulates morphogenetic movements of convergence and extension as well as epiboly through the G-protein-coupled PGE(2) receptor (EP4) via phosphatidylinositol 3-kinase (PI3K)/Akt. EP4 signaling is not required for proper cell shape or persistence of migration, but rather it promotes optimal cell migration speed during gastrulation. This work demonstrates a critical requirement of PGE(2) signaling in promoting cell motility through the COX-1-Ptges-EP4 pathway, a previously unrecognized role for this biologically active lipid in early animal development.

Animals↗
PubMed1988

Xenopus endo B is a keratin preferentially expressed in the embryonic notochord.

Screening of a cDNA library from neurula stage Xenopus laevis for notochord-specific sequences led to the isolation of a cDNA clone, XK endo B (Xenopus keratin endo B), which encodes a nonepidermal type I keratin. In situ and Northern blot hybridizations indicate that expression of XK endo B RNA is concentrated in the notochord, whereas expression in the endoderm is 5-10 times lower. XK endo B mRNA is present in the oocyte and increases from late gastrula. Accumulation peaks by late neurula and is greatly reduced by the tadpole stage; in the adult, a low level of XK endo B RNA is present in the liver. XK endo B shows sequence homology to mouse endo B; genomic Southern blots show that XK endo B is the most similar sequence to mouse endo B in the Xenopus genome, and vice versa, indicating that XK endo B and mouse endo B are homologs. The use of endo B as a marker and the germ layer derivation of the notochord are discussed in light of these results.

Amino Acid Sequence↗
PubMed1990

Identification of a retinoic acid-sensitive period during primary axis formation in Xenopus laevis.

Retinoic acid (RA) is able to profoundly alter patterning of the primary body axis in embryos of the frog Xenopus laevis. The response to RA is dose-dependent, and leads to progressive truncation of the anteroposterior axis, with anterior structures most sensitive. Both mesodermal and ectodermal tissues are affected, and in vitro assays demonstrate that induced dorsal ectoderm is one direct target of RA. RA represses expression of anterior-specific genes and concomitantly induces expression of at least one posterior-specific gene. Resistance to RA is acquired gradually, during gastrula and early neurula stages, with posterior structures becoming resistant before anterior structures. These data demarcate in the embryo an anterior "domain," which may define the head rudiment and which transcends germ layers. RA can alter the axial pattern after its initial induction; thus, RA sensitivity defines a labile intermediate that occurs during axial patterning. These data suggest a possible role for RA in normal axis formation.

Animals↗
PubMed1991

A retinoic acid receptor expressed in the early development of Xenopus laevis.

We have isolated cDNAs coding for a putative retinoic acid receptor (RAR) of the gamma-type from a Xenopus laevis neurula cDNA library. By transient cotransfection of COS cells with an expression vector and a reporter plasmid, this cDNA is shown to direct the synthesis of a retinoic acid-dependent transcription factor. In embryos of X. laevis, transcription of the corresponding gene is greatly enhanced during gastrulation and early neurulation. Two distinct areas with high abundance of RAR gamma mRNA are located at the anterior and at the posterior end of the neurula. The two maxima have emerged by the end of gastrulation and they become more pronounced during neurulation. At tailbud and early tadpole stages, the RAR transcripts are found mainly in the head mesenchyme and in the tailbud. The expression of this RAR is region-specific but not germ-layer-specific. The strong and stage-specific activation of zygotic transcription of this RAR gene, and the specific localization of the mRNA are consistent with the temporal and spatial pattern of retinoic acid sensitivity of X. laevis embryos. Therefore it is likely that the gene product mediates the effects of endogenous and of exogenous retinoic acid on early embryogenesis of Xenopus. The significance of these findings for the specification of the anteroposterior axis is discussed.

Amino Acid Sequence↗
PubMed1991

Retinoic acid perturbs the expression of Xhox.lab genes and alters mesodermal determination in Xenopus laevis.

Retinoic acid (RA) treatment of Xenopus laevis embryos leads to anterior truncation of the body axis (Durston et al. 1989; Sive et al. 1990). These initial studies suggested that RA may play a role in the patterning of the primary body axis. At least one target of RA was shown previously to be dorsal ectoderm. In this report we extend this observation and also ask whether RA alters the determination and inducing capacity of mesodermal tissue. To facilitate this analysis we isolated the homeo-domain-containing genes Xhox.lab1 and Xhox.lab2. These genes were expressed in both ectoderm and mesoderm during the RA-sensitive period and were strongly induced by RA in both germ layers. In particular, anterior regions expressed low levels of Xhox.lab RNAs in untreated embryos but showed increased expression after RA application. We show further that although RA-treated embryos contained anterior-inducing mesoderm, the amount of this activity appeared to be lower than that of controls. Additionally, we document that RA suppressed lateral (muscle) and ventral (blood) mesoderm differentiation. The data indicate that RA alters mesodermal determination and causes axial perturbation both by depressing the ability of dorsal mesoderm to induce anterior structures and by altering the response of dorsal ectoderm to induction. These analyses suggest that Xhox.lab genes may be responsible, in part, for mediating the RA effect.

Amino Acid Sequence↗
PubMed1993

Axial, a zebrafish gene expressed along the developing body axis, shows altered expression in cyclops mutant embryos.

Here, we report the cloning of a cDNA from zebrafish encoding a member of the fork head/HNF3 gene family. The gene, which we have called Axial, begins to be expressed just before gastrulation in a narrow region on the dorsal side of the embryo, the fish equivalent of the amphibian organizer. Expression can be detected in the involuted cells comprising the mesendoderm of the developing axis. At the end of gastrulation expression is turned on in the ventral neural plate in cells adjacent to the Axial-expressing mesodermal cells. Thus, Axial appears to be a target of both mesoderm induction and neural induction, leading to expression in cells of all three germ layers along the developing axis. Like the Brachyury gene. Axial is strongly induced by activin A, suggesting a role for endogenous activins in specifying the overlapping domains of expression of these two genes along the axis. Axial-expressing cells in the neuroectoderm include those of the future floor plate and cells of the ventral forebrain. In embryos homozygous for the cyclops mutation, expression is normal in mesendodermal cells but is absent from the ventral neural tube. The primary defects of cyclops mutants (lack of floor plate, deficiencies in the brain and cyclopia) correlate well with the expression domain of the Axial gene in wild-type neuroectoderm. The lack of Axial expression in cyclops neuroectoderm suggests that activation of Axial may be an immediate response of cyclops gene activity. Taken together, our data suggest that Axial plays a crucial role in specification of both the axial mesendoderm and the ventral central nervous system.

Activins↗
PubMed1995

Consequences of lack of beta 1 integrin gene expression in mice.

beta 1 integrins are cell-surface receptors that mediate cell-cell and cell-matrix interactions. We have generated a null mutation in the gene for the beta 1 integrin subunit in mice and embryonic stem (ES) cells. Heterozygous mice are indistinguishable from normal littermates. Homozygous null embryos develop normally to the blastocyst stage, implant, and invade the uterine basement membrane but die shortly thereafter. Using beta 1 integrin-deficient ES cells we have established chimeric embryos and adult mice. Analysis of the chimeric embryos demonstrated the presence of beta 1 integrin-deficient cells in all germ layers indicating that beta 1-null cells can differentiate and migrate in a context of normal tissue. When evaluated at embryonic day 9.5 (E9.5), embryos with a beta 1-null cell contribution below 25% were developing normally, whereas embryos with a contribution above this threshold were distorted and showed abnormal morphogenesis. In adult chimeric mice beta 1 integrin-deficient cells failed to colonize liver and spleen but were found in all other tissues analyzed at levels from 2%-25%. Immunostaining of chimeric mice showed that in cardiac muscle, there were small, scattered patches of myocytes that were beta 1-null. In contrast, many myotubes showed some beta 1-null contribution as a result of fusion between wild-type and mutant myoblasts to form mixed myotubes. The adult chimeric brain contained beta 1-null cells in all regions analyzed. Also, tissues derived from the neural crest contained beta 1 integrin-deficient cells indicating that migration of neuronal cells as well as neural crest cells can occur in the absence of beta 1 integrins.

Animals↗
PubMed1986

Epidermolysis bullosa acquisita antigen, a major cutaneous basement membrane component, is synthesized by human dermal fibroblasts and other cutaneous tissues.

The epidermolysis bullosa acquisita (EBA) antigen is identified as 2 chains: a 290,000-dalton protein and a less prominent 145,000-dalton protein. The 290,000-dalton chain is synthesized by human keratinocytes in culture. In this study, we show that the 290,000-dalton chain is synthesized by human skin fibroblasts and cutaneous human tumors. In contrast, HT1080 cells, a human sarcoma cell line known to produce matrix molecules (such as laminin and type IV collagen), does not synthesize the EBA antigen. Further, the EBA antigen is absent from serum and blood components, placenta, amnion, lung, and the EHS tumor, a murine sarcoma that produces large amounts of laminin, type IV collagen, nidogen, entactin, and basement membrane proteoglycan but is present in cutaneous tumors of adnexal and epithelial origin. These data suggest that while the EBA antigen is synthesized by both human skin keratinocytes and fibroblasts and is therefore not specific for a primordial germ layer, it does appear to be specific for tissue containing a stratified squamous epithelium.

Antigens↗
PubMed1978

Chondroectodermal dysplasia (Ellis--van Creveld syndrome) with dysplasia of renal medulla and bile ducts.

A case of a 28-month-old boy with chondroectodermal dysplasia (Ellis-van Creveld syndrome) is reported. Besides polydactyly, ectodermal dysplasia, acromelic dwarfism and congenital heart defect, which are characteristic morphologic features of the syndrome, additional dysplastic developmental defects were discovered in the kidneys, liver, and lungs. Detailed histopathologic studies of the growth plates of tibia, femur and ribs disclosed an irregular, partly hyperplastic, partly dystrophic appearance of the epiphyseal cartilage, which was not resorbed properly by the invading blood vessels. Focal areas of necrosis occurred and barriers of tongue-shaped cartilaginous peninsulas persisted. Regular enchondral ossification was hindered and compensatory membrane ossification was found in the fibrosing metaphyseal bone marrow adjacent to the cartilage. Dysplasia and fibrosis of the renal medulla plus interstitial fibrosing nephritis in the cortex resulted in kidney contraction and renal failure. Hepatomegaly, portal fibrosis and bile duct hyperplasia and dysplasia were detected at autopsy, but did not have any clinical significance. These findings once again emphasize that derivatives of all three germ layers are involved in the Ellis-van Creveld syndrome. The possibility that a single metabolic or structural abnormality of the mesenchymal tissues could be responsible for the various organ dysplasias is discussed.

Bile Ducts↗
PubMedDate not supplied

Intracranial malignant teratoma.

A case of malignant teratoma arising near the third ventricle in an adult is reported. It represented a true teratoma containing elements of all three germ layers of which two, namely the mesenchymal and endodermal elements have undergone malignant change. It was characterized by rapid recurrences after two operations with death occurring shortly after the second operation.

Adult↗
PubMed1979

No evidence for chromosomal mosaicism in multiple tissues of 10 patients with 45, XO Turner syndrome.

Why the frequency of spontaneous abortions among monosomy X conceptuses is 98% while the postnatal course of Turner syndrome is relatively benign has not been understood. One explanation could be that mosaicism for a euploid cell line confers viability and that those 2% of 45,XO zygotes surviving in utero have some degree of mosaicism. We thus reasoned that if the non-mosaic 45,XO karyotype is lethal, a thorough study of living Turner syndrome patients might reveal a much higher frequency of mosaicism than the 30--40% reported. Ten adult women with a 45,XO leukocyte karyotype were investigated, looking at five tissue types from all three germ layers: buccal mucosa and hair from ectoderm, urinary epithelium from endoderm and ectoderm, and lymphocytes and skin fibroblasts from mesoderm. We were unable to confirm mosaicism in these patients, although in 2 out of 10 there was the suggestion of a small percentage of euploid cells in skin and blood karyotypes.

Abortion, Spontaneous↗
PubMed1984

Cell-to-cell contact in primary embryonic induction: effects of lectin on electrical coupling and neural induction.

The effects of lectin (concanavalin A; ConA) on the electrical coupling between inducing chorda-mesoderm and reacting ectoderm cells, and the realization of neural induction were investigated. The electrical coupling between cells of the chorda-mesoderm of the late gastrula (stage 13b) and the competent ectoderm or Con-A-treated ectoderm of the early gastrula (stage 12a) was measured. Neural induction was tested with ectoderm explants which had been combined with the inducing chorda-mesoderm for 1, 3 and 6 h. Electrical coupling was observed after 3 h. By 6 h, the coupling ratio had recovered to the same level as that between the homogeneous germ-layer cells. However, the electrical coupling did not recover in the combinant with Con-A-treated ectoderm. This suggests that Con-A disturbs close cell contact between the ectoderm and chorda-mesoderm cells. Neural induction was realized in the ectoderm which was combined with chorda-mesoderm for more than 3 h; this occurred parallel to the recovery of electrical coupling. In contrast, Con-A treatment (50 micrograms/ml) of the competent ectoderm for 30 min prevented neural induction. After 3 h of contact, the neural induction of Con-A-treated ectoderm was only one-third of that of the control ectoderm. The present study suggests that cellular contact between the inducing mesoderm and the ectoderm target cells plays an important role in the realization of neural induction.

Animals↗
PubMed1987

The histone H1(0)/H5 variant and terminal differentiation of cells during development of Xenopus laevis.

The maintenance of the differentiated condition is supposed to be associated with the presence of a histone of the H1(0)/H5 subclass. If the H1(0)/H5 variant has an important role in differentiation distinct from that of H1, it should display differential expression in time and position during development. Here we report that this prediction is verified during Xenopus laevis development, in which tadpoles exhibit a very characteristic, developmentally regulated pattern of histone H1(0)/H5 expression that is different for the derivatives of each embryonic germ layer. However, the pattern of appearance of this variant during development does not reflect a simple correlation between its presence and the state of differentiation. Therefore, these results are pertinent to current ideas on differentiation and the involvement of lysine-rich histones in the repression of eukaryotic genes.

Aging↗
PubMed1987

Immortalization of precursors of endodermal, neuroectodermal and mesodermal lineages, following the introduction of the simian virus (SV40) early region into F9 cells.

F9 embryonal carcinoma cells were transfected with a hybrid plasmid containing the early genes of the simian virus SV40 under the control of the adenovirus type 5 E1A promoter [21]. These cells were induced to differentiate in aggregates in the presence of retinoic acid (RA). Unlike the derivatives of F9 that are usually obtained in this manner, the plasmid-containing cells were both programmed and immortalized; in addition, expression of the SV40 T antigen was now triggered. These immortalized cells could be separated into three classes: (1) extraembryonic derivatives, (2) embryonic differentiated tissues, (3) immature cells surrounding the differentiated cells. When injected into mice, the mixture of these cells gave rise to multipotential tumors. From the immature cells, committed precursors of the neuroectodermal, endodermal, and mesodermal pathways could be isolated by cloning and selection according to: (a) their specific pattern of differentiation in the tumors and (b) the occurrence of specific markers in the differentiated progeny. The isolation of stable immortalized cell lines corresponding to precursors of the three primitive germ layers and capable of differentiating reproducibly along a particular restricted pathway should facilitate molecular studies on early embryonic development in mouse.

Animals↗
PubMed1993

Appearance and distribution of entactin in the early chick embryo.

Entactin is a sulfated glycoprotein of basement membranes and recent data indicate that it may play a major role in extracellular matrix (ECM) assembly and in modulating the activities of the other molecular components. We investigated the time of appearance and subsequent distribution of entactin during the earliest stages of morphogenesis and its involvement in the first major cellular migrations and interactions in the chick embryo. Entactin is first detected in the epiblast and in the hypoblast at the blastula stage. The accumulating ECM displays intense presence of entactin in the space between the epiblast and the hypoblast at late blastula. Entactin is increasingly abundant in the neural plate and in the ECM and also at least transiently in many mesodermal tissues such as the notochord, the developing heart and somites in the early chick embryo. Immunogold labeling revealed a punctate pattern of entactin distribution in the ECM during the gastrula, neurula and at later stages and at all levels within the embryo. Because of its early appearance in more than one germ layer, entactin may be important in the formation of most embryonic structures. Entactin is detected at the same developmental time and co-localizes with laminin. Antibodies to entactin do not interfere with triggering of the first major cell movements but perturb directional migration of these cells. It would seem that entactin plays a functional role in the directed migration of cells and does not seem to affect cell adhesion during the period of the first morphogenetic events in the early chick embryo.

Animals↗
PubMed2004

Establishment and in vitro differentiation of a new embryonic stem cell line from human blastocyst.

Embryonic stem cells have the ability to remain undifferentiated and proliferate indefinitely in vitro while maintaining the potential to differentiate into derivatives of all three embryonic germ layers. These cells have, therefore, potential for in vitro differentiation studies, gene function, and so on. The aim of this study was to produce a human embryonic stem cell line. An inner cell mass of a human blastocyst was separated and cultured on mouse embryonic fibroblasts in embryonic stem cell medium with related additives. The established line was evaluated by morphology; passaging; freezing and thawing; alkaline phosphatase; Oct-4 expression; anti-surface markers including Tra-1-60 and Tra-1-81; and karyotype and spontaneous differentiation. Differentiated cardiomyocytes and neurons were evaluated by transmission electron microscopy and immunocytochemistry. Here, we report the derivation of a new embryonic stem cell line (Royan H1) from a human blastocyst that remains undifferentiated in morphology during continuous passaging for more than 30 passages, maintains a normal XX karyotype, is viable after freezing and thawing, and expresses alkaline phosphatase, Oct-4, Tra-1-60, and Tra-1-81. These cells remain undifferentiated when grown on mouse embryonic fibroblast feeder layers in the presence or absence of recombinant human leukemia inhibitory factor. Royan H1 cells can differentiate in vitro in the absence of feeder cells and can produce embryoid bodies that can further differentiate into beating cardiomyocytes as well as neurons. These results define Royan H1 cells as a new human embryonic stem cell line.

Alkaline Phosphatase↗
PubMed2004

Epidermal stem cells: interactions in developmental environments.

Homeostasis of continuously renewing adult tissues, such as the epidermis of the skin, is maintained by epidermal stem cells (EpiSC), which are a small population of undifferentiated, self-renewing basal keratinocyte cells that produce daughter transit amplifying (TA) cells to make up the majority of the proliferative basal cell population in the epidermis. We have isolated EpiSC from neonatal and adult skin, and shown that these cells can regenerate an epidermis that lasts long term in vitro and in vivo, and that permanently expresses a recombinant gene in the regenerated tissue (Bickenbach and Dunnwald, 2000; Dunnwald et al., 2001). When we injected murine EpiSC into the developing blastocyst environment of the mouse, we found that both neonatal and adult EpiSC retained some ability to participate in the formation of tissues from all three germ layers (Liang and Bickenbach, 2002; Bickenbach and Chinnathambi, 2004; Liang et al., 2004). Although it appears evident that EpiSC act as pluripotent stem cells, how this reprogramming takes place is not understood. EpiSC might directly transdifferentiate into other cell types or they might first dedifferentiate into a more primitive cell type, and then proceed to develop along a cell lineage pathway. To begin to unravel this, we co-cultured EpiSC with embryonic stem (ES) cells, and found that EpiSC could alter their cell lineage protein expression to that of a more primitive cell type. We also placed EpiSC in a wounded environment and found that EpiSC interacted with the mesenchymal cells repopulating the wound bed. Our findings indicate that the population of cells that we isolate as EpiSC has a pluripotent capability. This has led us to postulate a paradigm shift for somatic stem cells. We propose that tissues maintain a sequestered population of uncommitted stem cells that retain a regenerative response which is enhanced when the cells are exposed to developmental or stress influences.

Alkaline Phosphatase↗