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PubMed1981

[Ecto-mesodermal interactions and chick embryo limb chondrogenesis. Ultrastructural studies of cultures in the vitelline membrane (author's transl)].

Stage 17 (Hamburger and Hamilton) limb mesoderm, isolated and cultured in vitro differentiates into cartilage (11.5% of the explants). However, chondrogenesis is considerably improved in the presence of ectoderm, whether the interacting tissues are in close contact or separated by the vitelline membrane. Stage 15-16 limb mesoderm cultured in vitro is unable to differentiate into cartilage. Previous experiments have shown that a contact between ectoderm and mesoderm is necessary for the induction of cartilage to take place. However, when the vitelline membrane separates the two tissues, cartilage differentiation occurs in 16.3% of the explants. Can a contact between the two interacting tissues be established through the vitelline membrane? Ultrastructural studies of the relationships between ectodermal and mesodermal cells and the vitelline membrane have shown that such a contact can be achieved by means of long mesodermal cell processes penetrating deeply into the vitelline membrane.

Animals↗
PubMed1980

Limb-somite relationship: myogenic potentialities of somatopleural mesoderm.

Since 1977, CHEVALLIER et al. had the idea that, although limb muscle cells are usually of somitic origin, somatopleural cells could give rise to myocytes under certain experimental conditions. New experiments were undertaken in order to investigate further the differentiating capacities of the limb somatopleural mesoderm. Two-day quail limb somatopleural mesoderm was ectopically implanted into two-day chick hosts (into the flank, in place of the neural tube or between the neural alar plates) and the specificity of the muscle cells in the resulting ectopic limbs was analyzed 7 to 10 days later. The grafts were grouped as a function of the stage of segmentation of the adjacent somitic mesoderm at the time of excision. Grafts, whose adjacent somitic mesoderm was still unsegmented (before stage 15 pairs of somites for the wing grafts and 26 pairs of somites for the leg grafts) or in process of segmentation (stages 15 to 20 pairs of somites for the wing grafts, only) were considered, after histological investigation, as devoid of somitically derived myogenic cells at the time of transplantation. In 6 out of 29 cases, such grafts expressed the ability to differentiate quail muscle cells. It can therefore be admitted that the limb somatopleural mesoderm contains a labile population of cells able to adjust its differentiative capacities to the environment.

Animals↗
PubMed2002

Zygotic Wnt/beta-catenin signaling preferentially regulates the expression of Myf5 gene in the mesoderm of Xenopus.

Zygotic Wnt signaling has been shown to be involved in dorsoventral mesodermal patterning in Xenopus embryos, but how it regulates different myogenic gene expression in the lateral mesodermal domains is not clear. Here, we use transient exposure of embryos or explants to lithium, which mimics Wnt/beta-catenin signaling, as a tool to regulate the activation of this pathway at different times and places during early development. We show that activation of Wnt/beta-catenin signaling at the early gastrula stage rapidly induces ectopic expression of XMyf5 in both the dorsal and ventral mesoderm. In situ hybridization analysis reveals that the induction of ectopic XMyf5 expression in the dorsal mesoderm occurs within 45 min and is not blocked by the protein synthesis inhibitor cycloheximide. By contrast, the induction of XMyoD is observed after 2 h of lithium treatment and the normal expression pattern of XMyoD is blocked by cycloheximide. Analysis by RT-PCR of ectodermal explants isolated soon after midblastula transition indicates that lithium also specifically induces XMyf5 expression, which takes place 30 min following lithium treatment and is not blocked by cycloheximide, arguing strongly for an immediate-early response. In the early gastrula, inhibition of Wnt/beta-catenin signaling blocks the expression of XMyf5 and XMyoD, but not of Xbra. We further show that zygotic Wnt/beta-catenin signaling interacts specifically with bFGF and eFGF to promote XMyf5 expression in ectodermal cells. These results suggest that Wnt/beta-catenin pathway is required for regulating myogenic gene expression in the presumptive mesoderm. In particular, it may directly activate the expression of the XMyf5 gene in the muscle precursor cells.

Animals↗
PubMed1987

Cyclophosphamide, hexamethylmelamine, adriamycin and cisplatin combination chemotherapy in mixed mesodermal sarcoma of the female genital tract.

Clinically mixed mesodermal sarcoma is a different entity among the other subtypes of soft tissue sarcomas. Although adriamycin is considered to be the most active single agent in the treatment of adult soft tissue sarcomas, the drug has only limited activity in mixed mesodermal sarcomas. On the other hand, cisplatin is inactive in soft tissue sarcomas, but was reported to be active in mixed mesodermal sarcomas. Therefore combinations including both adriamycin and cisplatin appear attractive for testing in the treatment of mixed mesodermal sarcomas. We have performed a pilot study with two combinations in mixed mesodermal sarcomas of the female genital tract. Two patients treated with adriamycin and cisplatin showed rapid progression. Of 7 patients treated with cyclophosphamide, hexamethylmelamine, adriamycin and cisplatin (CHAP-5), 6 had measurable disease, of whom 5 yielded a response (2 complete responses for 19+ and 40 months and 3 partial responses for 4, 7 and 8 months). The patient with non-measurable disease had a progression-free survival of 27 months. The median survival for all CHAP-5-treated patients was 20 months. This regimen is recommended for further phase II studies.

Aged↗
PubMed2006

Retinoic-acid signalling in node ectoderm and posterior neural plate directs left-right patterning of somitic mesoderm.

Somitogenesis requires bilateral rhythmic segmentation of paraxial mesoderm along the antero-posterior axis. The location of somite segmentation depends on opposing signalling gradients of retinoic acid (generated by retinaldehyde dehydrogenase-2; Raldh2) anteriorly and fibroblast growth factor (FGF; generated by Fgf8) posteriorly. Retinoic-acid-deficient embryos exhibit somite left-right asymmetry, but it remains unclear how retinoic acid mediates left-right patterning. Here, we demonstrate that retinoic-acid signalling is uniform across the left-right axis and occurs in node ectoderm but not node mesoderm. In Raldh2(-/-) mouse embryos, ectodermal Fgf8 expression encroaches anteriorly into node ectoderm and neural plate, but its expression in presomitic mesoderm is initially unchanged. The late stages of somitogenesis were rescued in Raldh2(-/-) mouse embryos when the maternal diet was supplemented with retinoic acid until only the 6-somite stage, demonstrating that retinoic acid is only needed during node stages. A retinoic-acid-reporter transgene marking the action of maternal retinoic acid in rescued Raldh2(-/-) embryos revealed that the targets of retinoic-acid signalling during somitogenesis are the node ectoderm and the posterior neural plate, not the presomitic mesoderm. Our findings suggest that antagonism of Fgf8 expression by retinoic acid occurs in the ectoderm and that failure of this mechanism generates excessive FGF8 signalling to adjacent mesoderm, resulting initially in smaller somites and then left-right asymmetry.

Aldehyde Oxidoreductases↗
PubMedDate not supplied

An amphioxus nodal gene (AmphiNodal) with early symmetrical expression in the organizer and mesoderm and later asymmetrical expression associated with left-right axis formation.

The full-length sequence and zygotic expression of an amphioxus nodal gene are described. Expression is first detected in the early gastrula just within the dorsal lip of the blastopore in a region of hypoblast that is probably comparable with the vertebrate Spemann's organizer. In the late gastrula and early neurula, expression remains bilaterally symmetrical, limited to paraxial mesoderm and immediately overlying regions of the neural plate. Later in the neurula stage, all neural expression disappears, and mesodermal expression disappears from the right side. All along the left side of the neurula, mesodermal expression spreads into the left side of the gut endoderm. Soon thereafter, all expression is down-regulated except near the anterior and posterior ends of the animal, where transcripts are still found in the mesoderm and endoderm on the left side. At this time, expression also begins in the ectoderm on the left side of the head, in the region where the mouth later forms. These results suggest that amphioxus and vertebrate nodal genes play evolutionarily conserved roles in establishing Spemann's organizer, patterning the mesoderm rostrocaudally and setting up the asymmetrical left-right axis of the body.

Amino Acid Sequence↗
PubMed1986

Transplantation studies to investigate mesoderm-ectoderm adhesive cell interactions during gastrulation.

Experiments involving transplantation of the roof of the blastocoel in Rana pipiens embryos reveal that the inner surface of the roof of the blastocoel must be coated with a fibrous extracellular matrix (F-ECM) to serve as a substratum for mesodermal cell migration. When the roof of the blastocoel is inverted the original outer surface, now projecting toward the blastocoel, does not become coated with F-ECM and does not support mesodermal cell migration. When the roof of the blastocoel is removed from a normal embryo and transplanted into an interspecific arrested hybrid embryo known to be deficient in F-ECM synthesis, the grafted ectodermal fragment does not become coated with F-ECM and does not support normal mesodermal cell migration. When a hybrid graft is placed in a normal embryo, the grafted ectodermal fragment becomes coated with F-ECM and supports mesodermal cell migration. In normal control embryos migrating mesodermal cells are polarized due to formation of lamellipodia on their leading but not their trailing edges. These cells are arranged in overlapping layers. The leading cells form lamellipodia on the roof of the blastocoel and trailing cells form lamellipodia on one another.

Animals↗
PubMed2000

Requirement for BMP and FGF signaling during cardiogenic induction in non-precardiac mesoderm is specific, transient, and cooperative.

We previously reported that combined treatment with bone morphogenetic protein-2 (BMP-2) and fibroblast growth factor-4 (FGF-4) induces cardiogenic events culminating in full cardiac differentiation of non-precardiac mesoderm explanted from stage 6 avian embryos (Lough et al. [1996] Dev. Biol. 178:198-202.). To elucidate the respective functions of BMP and FGF in initiating and maintaining the cardiogenic process, we have used these ectopic cells as a cardiac specification model to ascertain requirements for growth factor specificity and extent of application, as well as induction of cardiac transcription factors. The inability of some BMP isoforms to replace the inductive activity of BMPs-2/4 indicated a specific requirement for this signaling pathway; moreover, neither activin-A nor insulin, which support terminal differentiation of precardiac mesoderm, nor leukocyte inhibitory factor (LIF), which promotes hypertrophy in cardiac myocytes, could replace BMP's cardiogenic activity. A similarly specific requirement for FGF-2/4 signaling was revealed since neither FGF-7, activin-A nor insulin could replace this activity. The effect of both factors was concentration-dependent; maximal incidence of explant differentiation for each occurred at 50 ng/ml. Surprisingly, the majority of explants treated with high BMP levels (250 ng/ml) exhibited a non-cardiac phenotype that was characterized by intense expression of alkaline phosphatase, suggesting differentiation toward an alternative mesodermal phenotype. Experiments to assess the duration of exposure to each factor that was required revealed that while exposure to BMP and FGF during only the initial 30 min of a 48-hr culture period was sufficient to induce cardiogenesis in a significant percentage of explants, 100% incidence of explant differentiation was obtained only when FGF treatment was restricted to the first 30 min and BMP was continuously present during the 48-hr culture period. Treatment with both growth factors was required to induce the cardiac transcription factors cNkx-2.5 and SRF; neither mRNA was induced by BMP or FGF alone. These findings indicate that: (1) specific members of the BMP and FGF families are required to induce cardiogenesis in non-precardiac mesoderm; (2) BMPs-2/4 may function as a morphogen; (3) brief application of both factors can induce cardiogenesis in a modest number of explants whereas (4) 100% incidence of explant differentiation can only be attained by brief FGF treatment combined with continuous BMP treatment and (5) both factors are necessary to induce downstream cardiac transcription factors. These findings are interpreted in terms of these factors' possible roles during cardiac specification and differentiation.

Bone Morphogenetic Protein 2↗
PubMed2000

Histone acetylation is a checkpoint in FGF-stimulated mesoderm induction.

We have previously demonstrated that the transcription factor, AP-1 (c-jun/c-fos heterodimer), mediates fibroblast growth factor (FGF) signaling during mesoderm induction in Xenopus embryo. In the present studies, we show that histone acetylation is involved in FGF-mediated signaling leading to mesoderm induction. Histone acetylation is a dynamic process regulated by the activities of two histone-modifying enzymes, the histone acetyltransferase(s) and histone deacetylase(s) (HDACs). We found that basal and FGF-regulated activator protein 1 (AP-1) activity in Xenopus embryo is markedly reduced by treatment of trichostatin A (TSA), a specific inhibitor of HDAC. However, activity of another transcription factor, NFkappaB, is enhanced by TSA treatment. AP-1-mediated mesoderm induction in the animal caps is dramatically suppressed by TSA at a dose-dependent manner. This suppression can be rescued by ectopic expression of HDAC3 at early stage. Finally, we found that histone acetylation in animal caps is inhibited by FGF whereas enhanced by TSA (as a control). Therefore, we propose that histone acetylation is a checkpoint for transduction of the FGF/AP-1 signals to induce mesoderm. Published 2000 Wiley-Liss, Inc.

Acetylation↗
PubMed1988

Formation and differentiation of extraembryonic mesoderm in the rhesus monkey.

Differentiation of extraembryonic mesoderm in the rhesus monkey was studied from the epithelial penetration stage of implantation (stage 4) through the first week of postimplantation development (to stage 6). It was found that the first cells that appeared between the primitive endoderm (hypoblast) and trophoblast were separated from the latter by a basal lamina but appeared to be either loosely attached to the endoderm or to have been detached from it. Cells in this intermediate position differentiated cytologically into mesenchymal cells, which, by stage 5, had a distinctive intraendoplasmic reticulum marker. This differentiation occurred prior to the time at which the primitive streak could be recognized. By the time the primitive streak was readily discernible (stage 6), the extraembryonic mesoderm had already produced substantial extracellular matrix. The sequence of differentiation was repeated, with a 1- to 2-day lag, in the secondary implantation site. No evidence of a contribution from cytotrophoblast or primitive streak to the extraembryonic mesoderm was found. It is concluded that the origin of the first extraembryonic mesoderm in the rhesus monkey is probably a two-step process, with formation of a reticulum from primitive endoderm followed by differentiation in situ into mesenchymal cells. The first blood vessels formed also differentiated in situ from the extraembryonic mesenchymal cells. Primitive capillaries were identifiable as early as the 13th day of pregnancy.

Animals↗
PubMed1993

Expression of Xenopus snail in mesoderm and prospective neural fold ectoderm.

Expression of the Xsna gene during Xenopus laevis embryogenesis has been analysed by in situ hybridisation. Like its homologue snail in Drosophila, Xsna is expressed zygotically in all early mesoderm. Expression starts during stage 9 in the dorsal marginal zone and spreads to the ventral side by stage 10. During gastrulation, each cell begins to express as it involutes so that cells newly expressing Xsna are added to the forming mesoderm mantle in an anterior-to-posterior progression. Xsna expression is then down-regulated in a tissue-specific fashion that reveals the subdivision of the mesoderm before its derivatives are overtly differentiated; e.g., the appearance of the notochord, myotomes, and pronephroi are preceded by the disappearance of Xsna mRNA, while undifferentiated mesoderm remains labelled, even into tadpole stages. Xsna is expressed in the suprablastoporal endoderm during gastrulation and in its derivatives, the prechordal and sub-notochordal endoderm, during neurulation. Relationships between Xbra, Xtwi, and Xsna expression are examined. Xsna is also expressed in the prospective neural fold ectoderm from stage 11 in a low arc above the dorsal marginal zone, precisely identifying a distinct band of cells that surrounds the prospective neural plate that we designate the neural plate border. The anterior transverse neural fold, which becomes forebrain, ceases Xsna expression during neurulation. In the longitudinal neural folds, the deep and superficial ectoderm compartments labelled by Xsna expression are the prospective neural crest and prospective roof of the neural tube, respectively. Xsna expression persists in the neural crest during migration and in some derivatives at least until metamorphosis but ceases in the roof of the neural tube soon after neurulation.

Animals↗
PubMed2002

Epithelial-mesenchymal transitions: a mesodermal cell strategy for evolutive innovation in Metazoans.

Epithelial-mesenchymal transitions (EMTs) are well known processes in which new mesenchyme is locally generated from epithelia. During the development of the vertebrate embryo, EMTs are a source of mesenchyme in diverse places and stages through embryonic morphogenesis, especially in mesodermal domains. In the present work we consider the embryo as a two-state system in which epithelium and mesenchyme represent the stable and unstable states, respectively. We think that a pattern of recurrent oscillations between the plasticity and exploratory behaviour of the mesenchyme and the stability of the epithelia can be recognized in the embryogenesis of vertebrates and, probably, in most tripoblastic Metazoans. Mesoderm, in particular, might be regarded as a cell layer able to oscillate between epithelial and mesenchymal states. The cellular and molecular mechanisms that enable these recurrent oscillations between stable (epithelial) and unstable (mesenchymal) states during embryogenesis provide the mesoderm with a large plasticity, an extended potential for innovation, and a better control of the three-dimensional (3D) body organization. In this scenario, it is conceivable that the origin of the mesoderm itself might be related to ancestral mechanisms regulating cell adhesion and detachment. We conclude that EMTs played a key role in the evolution of Metazoans, and are involved in the pathological and reparative processes of adult organisms.

Animals↗
PubMed2001

Brachyury, the blastopore and the evolution of the mesoderm.

The role of Brachyury and other T-box genes in the differentiation of mesoderm and endoderm of vertebrates is well established. Recently, homologues of Brachyury have been isolated from an increasing number of diverse organisms ranging from Cnidaria to vertebrates and insects. Comparative expression and function analysis allows the origin of the mesoderm and the evolution of the developmental role of Brachyury gene family in metazoans to be traced. The data suggest that an ancestral function of Brachyury was to designate a blastoporal region that had distinct properties in induction and axis elongation. A subset of blastoporal cells expressing Brachyury and other genes that convey specific mesodermal functions may have segregated as a distinct cell population from this region in the course of mesoderm evolution.

Animals↗
PubMed2004

Ventral tail bud mesenchyme is a signaling center for tail paraxial mesoderm induction.

A large body of evidence from several systems indicates that formation of the vertebrate tail is morphogenetically continuous with gastrulation, including neural inducing activity in descendants of the gastrula organizer. However, the signaling centers and molecular events regulating tail mesoderm induction and its organized elongation remain poorly defined. In mammals, the ventral ectoderm ridge (VER) is essential to maintain ongoing formation of paraxial mesoderm and somitogenesis in cultures of intact tail. Avian tail buds contain a similar VER structure. Here, we report that the chick ventral tail bud operates as a signaling center for paraxial mesoderm induction. By using "organizer" style grafting assays to early host embryos, we found that ventral tail bud was able to induce elongated paraxial mesodermal extensions and that the ventral tail bud mesenchyme underlying the VER is both necessary and sufficient for the induction in this assay system. Our observations combined with those of others suggest that interplay between several different signaling centers in the amniote tail bud regulates the coordinate induction and elongation of axial and paraxial structures in the developing tail.

Animals↗
PubMed2004

Twist is required for patterning the cranial nerves and maintaining the viability of mesodermal cells.

Twist encodes a basic helix-loop-helix transcription factor that is required for normal craniofacial morphogenesis in the mouse. Loss of Twist activity in the cranial mesenchyme leads to aberrant migratory behaviour of the neural crest cells, whereas Twist-deficient neural crest cells are located in an inappropriate location in the first branchial arch and display defective osteogenic and odontogenic differentiation (Soo et al. [2002] Dev. Biol. 247:251-270). Results of the present study further show that loss of Twist impacts on the patterning of the cranial ganglia and nerves but not that of the peripheral ganglia and nerves in the trunk region of the body axis. Analyses of the expression of molecular markers of early differentiation of the paraxial mesoderm and the histogenetic potency of somites of Twist(-/-) embryos reveal that Twist-deficient somites can differentiate into muscles, cartilage, and bones, albeit less prolifically. Twist function, therefore, is not essential for mesoderm differentiation. The poor growth of the Twist-deficient somites after transplantation to the ectopic site may be attributed to reduced proliferative capacity and extensive apoptosis of the paraxial mesoderm, suggesting that Twist is required for maintaining cell proliferation and viability in the mesodermal progenitors.

Animals↗
PubMed2007

Tbx1 regulation of myogenic differentiation in the limb and cranial mesoderm.

The T-box transcription factor Tbx1 has been implicated in DiGeorge syndrome, the most frequent syndrome due to a chromosomal deletion. Gene inactivation of Tbx1 in mice results in craniofacial and branchial arch defects, including myogenic defects in the first and second branchial arches. A T-box binding site has been identified in the Xenopus Myf5 promoter, and in other species, T-box genes have been implicated in myogenic fate. Here we analyze Tbx1 expression in the developing chick embryo relating its expression to the onset of myogenic differentiation and cellular fate within the craniofacial mesoderm. We show that Tbx1 is expressed before capsulin, the first known marker of branchial arch 1 and 2 muscles. We also show that, as in the mouse, Tbx1 is expressed in endothelial cells, another mesodermal derivative, and, therefore, Tbx1 alone cannot specify the myogenic lineage. In addition, Tbx1 expression was identified in both chick and mouse limb myogenic cells, initially being restricted to the dorsal muscle mass, but in contrast, to the head, here Tbx1 is expressed after the onset of myogenic commitment. Functional studies revealed that loss of Tbx1 function reduces the number of myocytes in the head and limb, whereas increasing Tbx1 activity has the converse effect. Finally, analysis of the Tbx1-mesoderm-specific knockout mouse demonstrated the cell autonomous requirement for Tbx1 during myocyte development in the cranial mesoderm.

Animals↗
PubMed1993

The Xenopus platelet-derived growth factor alpha receptor: cDNA cloning and demonstration that mesoderm induction establishes the lineage-specific pattern of ligand and receptor gene expression.

We have cloned the Xenopus PDGF alpha receptor cDNA and have used this clone, along with cDNA encoding PDGF A, to examine their expression pattern in Xenopus embryos and to determine the factors responsible for lineage specificity. Recombinant Xenopus alpha receptor expressed in COS cells exhibits PDGF-A-dependent tyrosine kinase activity. We find that receptor mRNA is present in cultured marginal zone tissue explants and in animal cap tissue induced to form mesoderm either by grafting to vegetal tissue or by treatment with recombinant activin A. In contrast, PDGF A mRNA is expressed in cultured, untreated animal cap tissue and is suppressed by mesoderm induction. These results suggest that ectodermally produced PDGF A may act on the mesoderm during gastrulation and that mesoderm induction establishes the tissue pattern of ligand and receptor expression.

Amino Acid Sequence↗
PubMed1987

Specific expression of the Hox 1.3 homeo box gene in murine embryonic structures originating from or induced by the mesoderm.

The murine Hox 1.3 homeo box-containing gene is expressed largely in mesoderm-derived or mesoderm-induced embryonal structures, as evidenced by in situ hybridization techniques. Expression is spatially limited to the thoracic region, specifically to components of segmental origin such as embryonal ribs and vertebrae and their precursors such as the equivalent sclerotomes, somites and somatic condensations. In addition, expression can be found in parts of embryonal lung, stomach tissue, gut and kidney, tissues whose formation is based on induction of region-specific mesoderm, as well as in some ectoderm-derived tissues. The expression is temporally controlled for the transcripts and can only be detected while the thoracic structures are being formed (days 8-13), but not at day 18 of gestation when the embryo is mature. These data suggest a role of Hox 1.3 gene in the generation of tissues derived from or induced by the embryonal mesoderm.

Animals↗