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PubMed2000

The mesoderm specification factor twist in the life cycle of jellyfish.

The basic helix-loop-helix (bHLH) transcription factor Twist is highly conserved from Drosophila to vertebrates and plays a major role in mesoderm specification of triploblasts. The presence of a Twist homologue in diploblasts such as the cnidarian Podocoryne carnea raises questions on the evolution of mesoderm, the third cell layer characteristic for triploblasts. Podocoryne Twist is expressed in the early embryo until the myoepithelial cells of the larva differentiate and then again during medusa development. There, the gene is detected first when the myoepithelial cells of the polyp dedifferentiate to form the medusa bud and later Twist is found transiently in the entocodon, a mesoderm-like cell layer which differentiates into the smooth muscle and striated muscle of the bell. On the other hand, in later bud stages and the medusa, expression is seen where non-muscle tissues differentiate. Experimental analysis of in vitro transdifferentiation and regeneration demonstrates that Twist activity is not needed when isolated striated muscle regenerate medusa organs. Developmental roles of Twist are discussed with respect to early animal evolution from a common ancestor of cnidarians and bilaterians.

Amino Acid Sequence↗
PubMed2001

Neural induction in the absence of mesoderm: beta-catenin-dependent expression of secreted BMP antagonists at the blastula stage in Xenopus.

A growing body of work indicates that neural induction may be initiated prior to the establishment of the gastrula mesodermal organizer. Here, we examine neural induction in Xenopus embryos in which mesoderm induction has been blocked by Cerberus-short, a reagent that specifically inhibits Nodal-related (Xnr) signals. We find that extensive neural structures with cyclopic eyes and brain tissue are formed despite the absence of mesoderm. This neural induction correlates with the expression of chordin and other BMP inhibitors-such as noggin, follistatin, and Xnr3-at the blastula stage, and requires beta-Catenin signaling. Activation of the beta-Catenin pathway by mRNA microinjections or by treatment with LiCl leads to differentiation of neurons, as well as neural crest, in ectodermal explants. Xnr signals are required for the maintenance, but not for the initiation, of BMP antagonist expression. Recent work has demonstrated a role for beta-Catenin signaling in neural induction mediated by the transcriptional down-regulation of BMP-4 expression. The present results suggest an additional function for beta-Catenin, the early activation of expression of secreted BMP antagonists, such as Chordin, in a preorganizer region in the dorsal side of the Xenopus blastula.

Animals↗
PubMed2002

Targeted deletion of the MLC1f/3f downstream enhancer results in precocious MLC expression and mesoderm ablation.

The expression of skeletal muscle contractile proteins is tightly regulated during embryonic development. In the mouse, the myosin light chain (MLC) 1f/3f gene locus is not activated until E9.5, exclusively in skeletal muscle precursor cells. A potent enhancer downstream of the MLC1f/3f locus confers correct temporal and spatial activation of linked reporter gene in transgenic mouse embryos. To examine roles of the MLC downstream enhancer (MLCE) in its native context of the MLC1f/3f gene locus, we eliminated a 1.5-kb DNA segment containing the enhancer from the mouse genome by targeted deletion, leaving no exogenous sequences at the deletion site. Mouse embryos homozygous for the MLCE deletion were smaller and developmentally delayed, formed no mesoderm by E7.5, and were resorbed almost completely at E8.5. In situ hybridization and RT-PCR analyses of affected mutant embryos at E7.5 revealed ectopic MLC transcripts, whose products would be predicted to interfere with a variety of nonmuscle cell functions determining differentiation of mesoderm. These results suggest that the MLC downstream enhancer and its flanking sequences include negative regulatory elements which block precocious activation of MLC expression in mesodermal precursors during a critical window of development, as well as positive elements which subsequently permit tissue-restricted MLC transcription in differentiating skeletal muscles.

Animals↗
PubMed2002

Conservation of Brachyury, Mef2, and Snail in the myogenic lineage of jellyfish: a connection to the mesoderm of bilateria.

One major difference between simple metazoans such as cnidarians and all the bilaterian animals is thought to involve the invention of mesoderm. The terms diploblasts and triploblasts are therefore, often used to group prebilaterian and bilaterian animals, respectively. However, jellyfish contain well developed striated and smooth muscle tissues that derive from the entocodon, a mesoderm-like tissue formed during medusa development. We investigated the hypothesis, that the entocodon could be homologous to the third germ layer of bilaterians by analyzing the structures and expression patterns of the homologues of Brachyury, Mef2, and Snail in the jellyfish Podocoryne carnea. These are regulatory genes from the T-box, MADS-box and zinc finger families known to play important roles in bilaterian mesoderm patterning and muscle differentiation. The sequence and expression data demonstrate that the genes are structurally and functionally conserved and even more similar to humans or other deuterostomes than to protostome model organisms such as Drosophila or Caenorhabditis elegans. Based on these data we conclude that the common ancestor of the cnidarians and bilaterians not only shared genes that play a role in regulating myogenesis but already used them to develop and differentiate muscle systems similar to those of triploblasts.

Animals↗
PubMed1993

Chondrogenesis in chick limb bud mesodermal cells: reciprocal modulation by activin and inhibin.

Activin and inhibin are members of the transforming growth factor-beta superfamily sharing a common beta-subunit, but with opposite biological activities on the release of follicle-stimulating hormone from pituitary. Recent studies have demonstrated that activin is the long sought after mesoderm induction factor in amphibians. To determine if activin and inhibin affect the proliferation and differentiation of chick limb bud mesodermal cells during cartilage formation of the limb, recombinant human activin A and inhibin A were tested on stage 24 chick limb bud mesodermal cells. The results showed that activin A has an inhibitory effect on chondrogenic differentiation, as indicated by Alcian blue staining and decreased [35S]sulfate incorporation into proteoglycans. In addition, the expression of type II collagen mRNA, a specific phenotypic marker of cartilage, was greatly inhibited when cultures were exposed to activin A for 5 days at a dose of 10 ng/ml. In contrast, inhibin A stimulated cartilage formation, as indicated by increased expression of type II collagen mRNA and synthesis of proteoglycans. These results imply that activin A and inhibin A can modulate chondrogenesis during differentiation of limb bud cells in culture.

Activins↗
PubMed1994

Maturation of myogenic and chondrogenic cells in the presomitic mesoderm of the chick embryo.

The establishment of cells with myogenic or chondrogenic potential is temporally and spatially separated from terminal differentiation in the developing chick embryo. Both cell types arise from tissue adjacent to the neural tube and notochord, the paraxial mesoderm. A cell culture system was developed in order to study the maturation and differentiation of myogenic and chondrogenic cells along the length of the paraxial mesoderm at different stages of development. Somite and segmental plate cells obtained from 36- to 52-h (stages 10-15) embryos were plated as a monolayer on substrata of gelatin, fibronectin, or laminin. A substratum of gelatin plus fibronectin was most effective in supporting adhesion and differentiation. Maximal increase in number of cells in somite cultures occurred 24 h earlier than that in segmental plate cultures. Fewer skeletal muscle cells and chondroblasts were present in cultures prepared from progressively more caudal regions of the paraxial mesoderm and from younger embryos. Some cells present within the somites and the rostral two-thirds of the stage 13 segmental plate differentiated without replication after placement in culture. Only the progeny of cells from its caudal third, and from stage 10 somites and segmental plates, differentiated under these conditions. The results suggest that some myogenic and chondrogenic cells obtain the ability to differentiate under these in vitro conditions after stage 10 of development, as they occupy more rostral positions within the segmental plate relative to the addition of cells at its caudal end. Although some stage 13 segmental plate cells form skeletal muscle and cartilage directly after removal from the embryo, differentiation is not observed in ovo until these cells are incorporated into somites, a minimum of 10 h later. Three-dimensional tissue interactions, and/or cell-cell interactions, while not required for segmental plate cells to undergo myogenesis and chondrogenesis, may play a role in regulating the timing of terminal differentiation within the embryo.

Animals↗
PubMed1996

A population of cells isolated from rat heart capable of differentiating into several mesodermal phenotypes.

A population of stem cells has been isolated from embryonic avian and neonatal rat skeletal muscle. These cells differentiate into several mesodermal phenotypes in culture upon treatment with dexamethasone. This study reports the isolation of a similar population of stem cells from another mesodermal tissue, the heart. Hearts were excised from 3- to 5-day- old rats, minced, and treated with a collagenase-dispase solution. Single cells were collected by centrifugation, washed, and plated in dishes. The cells were grown to confluence, trypsinized, and frozen at -80 degrees C in 7.5% dimethylsulfoxide. After at least 24 hr, the cells were thawed and plated in 24-well plates and treated with media containing dexamethasone at concentrations of 10(-6)-10(-10) M for 4 weeks. Control cultures contained mononucleated cells with a stellate morphology. Treatment with dexamethasone resulted in the appearance of several mesodermal phenotypes. Bone and cartilage nodules were identified with von Kossa and Alcian blue staining respectively. Adipocytes were identified using Sudan black B stain. Smooth muscle cells were identified by an anti-smooth muscle alpha-actin antibody, and skeletal myotubes were stained with anti-myosin antibody. Large binuclear cells with obvious fibers were noted and stained with anti-desmin. These binuclear cells appeared in both the control and the dexamethasone-treated cultures and were tentatively identified as cardiomyocytes. These data strongly suggest the existence of a population of mesenchymal stem cells in neonatal rat heart.

Animals↗
PubMed1991

Early mesoderm differentiation in the chick embryo.

Two groups of experiments were carried out. In the first group, grafts of quail mesoderm whose presumptive fate was to form somites or heart tissues, were taken from quail embryos (stage 4-5 of Hamburger and Hamilton 1951) and inserted beneath the ectoderm of chick embryos of stage 3-4 immediately lateral to the primitive streak. Whilst most grafts contributed to the somites and or the heart, 22 out of a total of 46 were found to have contributed also to the pharyngeal endoderm. Although three of these grafts were known to have included some quail endoderm cells, the remainder were considered to consist of mesoderm alone. It is concluded that mesoderm at the primitive streak stages is still capable of forming endoderm. In the second group of experiments, grafts of quail somites (stage 10-14) were inserted beneath the ectoderm of chick embryos of stage 3-4. In 18 out of 23 cases the graft cells were found in somitic tissue, but they were also found in the endoderm (4 specimens), lateral plate (3 specimens) and endothelium (4 specimens). It is concluded that even at stages 10-14, the somite-derived cells are still not completely determined to form somite derivatives. In those cases where the grafted somites differentiated further, sclerotome cells which migrated from them did not necessarily move towards the host notochord.

Animals↗
PubMed1991

Distribution and migration of angiogenic cells from grafted avascular intraembryonic mesoderm.

The hemangiogenic potencies of initially avascular intra-embryonic mesoderm were studied in chick and quail embryos and in chick-quail chimeras. The prechordal mesoderm, primitive streak and primitive node of quail embryos were heterospecifically grafted into limb buds of chick embryos. Hemangiopoietic quail cells in the host limb were detected by immunohistological staining with the monoclonal anti-MB-1 antibody after 3-6 days of re-incubation. The antibody is specifically directed against quail hemangiopoietic cells and their derivatives. Quail endothelial cells were found in pure quail and in chimeric vessels, inside as well as outside the graft. The main artery of the limb and the vessels inside the graft were connected by chimeric arteries. Proximal to the graft, quail endothelial cells were located predominantly within the lining of the main artery, while distally they were found mainly in the veins and the marginal sinus. The results show that, as early as stage 3 (according to Hamburger and Hamilton 1951, HH) all parts of the avascular intraembryonic mesoderm tested, give rise to endothelial cells. Both mechanisms, angiogenesis and vasculogenesis, contribute to the vascularization of the limb. Immunocytological and scanning electron microscopic studies indicate that centrifugal and centripetal migration of angiogenic cells occurs outside the vessels as well as on the inner surface of the endothelium.

Animals↗
PubMed1993

Ultrastructural localization of laminin subunits during the onset of mesoderm formation in the mouse embryo.

Using ultrastructural immunogold histochemistry on LR-Gold-embedded 6- and 7-day-old mouse embryos we investigated the appearance of the A- and B1-chains of the laminin molecule during mesoderm formation. With the help of antibodies against the A-chain and the E4 fragment of the B1-chain of the laminin molecule we were able to detect the subunits in vivo. Staining for the E4 fragment of the short arm of the laminin molecule from day 6 was negative. In contrast, strong staining for the A-chain of laminin was observed. Our results show, that the A-chain of laminin appears before the B1-chain in the 6-day-old mouse embryo before a basement membrane is seen between the ectodermal and entodermal cell layers. Furthermore, the staining pattern indicates, that the laminin molecule changes its orientation in the basement membrane of the ectoderm during mesoderm formation. On day 7 staining for the A-chain of laminin and for the E4 fragment was seen in a random distribution throughout the entire basement membrane, whereas in areas were the onset of mesoderm formation was taking place, the E4 fragment was restricted to the edge of the disintegrating basement membrane.

Animals↗
PubMed1979

The effect of cytochalasin B on chick mesoderm cells as studied by scanning electron microscopy.

The effects of cytochalasin B (CCB) on chick mesoderm cells in vivo was examined by scanning electron microscopy (SEM). The embryos were mounted for New Culture and the mesoderm exposed by dissecting off the endoderm. Cytochalasin B was suspended in saline and the embryos flooded with the suspension. Control embryos were treated with saline alone. The embryos were reincubated for varying times at 37 degrees C. In the treated embryos the mesoderm cells were rounded and separated from each other. Many had long branched processes and rough surfaces. These changes became more pronounced as treatment time was increased. They were also reversible on reincubating treated embryos in the absence of cytochalasin B. The morphological changes produced by CCB are thought to be due to an effect on the cytoskeleton, either a direct disruptive effect or detachment of skeletal microfilaments from the cell membrane. There may also be a direct removal of cell surface materials leading to the observed surface roughening of treated cells.

Animals↗
PubMed1995

Mesoderm-specific B104 expression in the Drosophila embryo is mediated by internal cis-acting elements of the transposon.

The Drosophila melanogaster genome contains about 100 copies of the B104 transposable element, which is strongly expressed during embryogenesis. Here we show that B104 expression is restricted to the esophageal and amnioproctodeal regions of the embryo and to the developing mesoderm. Mesoderm-specific B104 expression requires the activity of the mesoderm-determining factors twist and snail. Virtually the same expression patterns were observed in Drosophila yakuba, a species that a separated from D. melanogaster by some 15 million years of evolution. We show that B104 expression is directed by internal sequences of the retrotransposon that are capable of acting as a cis-acting regulatory element in front of a heterologous Drosophila promoter. Our findings suggest that retrotransposon insertions can affect the expression patterns of endogenous genes by adding and distributing specific cis-acting control elements throughout the host genome. We therefore propose that transposable elements in addition to reducing the fitness of their hosts may also provide a rich pool of cis-acting sequences that contribute to the long-term evolutionary potential of the population in a beneficial manner.

Amino Acid Sequence↗
PubMed2004

Simultaneous bilateral occurrence of a mixed mesodermal tumor and cystadenocarcinoma in the ovary.

The mixed mesodermal tumor is a very uncommon malignancy. The aggressiveness of this lesion is illustrated by extremely poor prospects for afflicted patients: postoperative survival is usually shorter than 24 months. According to the literature, malignant mixed tumor of the ovary is rather rare and its occurrence with other malignancy is exceptional. We report here a case of a 62-years old woman with serous cystadenocarcinoma in the right ovary and a heterologous malignant mixed mesodermal tumor in the left one. Both tumors expressed cytokeratins, while only the mesodermal tumor expressed S-100 and focal NSE.

Biomarkers, Tumor↗
PubMed1998

An amphioxus snail gene: expression in paraxial mesoderm and neural plate suggests a conserved role in patterning the chordate embryo.

Homologs of the Drosophila snail gene have been characterized in several vertebrates. In addition to being expressed in mesoderm during gastrulation, vertebrate snail genes are also expressed in presumptive neural crest and/or its derivatives. Given that neural crest is unique to vertebrates and is considered to be of fundamental importance in their evolution, we have cloned and characterized the expression of a snail gene from amphioxus, a cephalochordate widely accepted as the sister group of the vertebrates. We show that, at the amino acid sequence level, the amphioxus snail gene is a clear phylogenetic outgroup to all the characterized vertebrate snail genes. During embryogenesis snail expression initially becomes restricted to the paraxial or presomitic mesoderm of amphioxus. Later, snail is expressed at high levels in the lateral neural plate, where it persists during neurulation. Our results indicate that an ancestral function of snail genes in the lineage leading to vertebrates is to define the paraxial mesoderm. Furthermore, our results indicate that a cell population homologous to the vertebrate neural crest may be present in amphioxus, thus providing an important link in the evolution of this key vertebrate tissue.

Amino Acid Sequence↗
PubMed2004

Control of the temporal and spatial Uncx4.1 expression in the paraxial mesoderm of avian embryos.

Uncx4.1 is a homeobox containing transcription factor that determines the development of the pedicles of the neural arches, transverse processes and proximal ribs. In this paper we characterize the expression pattern of Uncx4.1 during chick embryogenesis with special focus on its expression in the paraxial mesoderm. In the presomitic mesoderm, Uncx4.1 is expressed in the caudal halves of the somites I and II. In the newly formed somites, Uncx4.1 expression remains in the caudal somite halves but becomes restricted to the somitocoele and the ventral epithelial wall. After somite compartmentalization, Uncx4.1 is expressed in the caudal half of the sclerotome in a well defined spatial and temporal pattern. Micromanipulations revealed that Uncx4.1 expression in the presomitic mesoderm is independent of signals from the axial structures and presumably induced by the intrinsic Notch/Delta driven oscillator activity that determines craniocaudal somite polarity. In contrast, in the maturing somite Uncx4.1 expression depends on signals from the axial structures. The notochord-floor plate complex is essential for maintaining Uncx4.1 expression in the caudal somite half. The neural tube is necessary for providing sufficient Uncx4.1 positive sclerotomal material to enable development of pedicles of the neural arches and transverse processes.

Animals↗
PubMed1999

The anchoring zone in the human placental amnion: bunches of oxytalan and collagen connect mesoderm and epithelium.

This study deals with the examination of the elastic fibre system as well as collagen fibrils and collagen type IV in the amnion of the human chorionic plate of uncomplicated pregnancies at term. In organs other than placenta, the elastic fibre system comprises elastic fibres, elaunin and oxytalan microfibrils. The investigation was performed by light and electron microscopy and immunocytochemistry. Abundant oxytalan fibres were present in all amnionic layers, while no elastic fibres were found. Oxytalan microfibrils formed a broad sub-epithelial layer and were intermingled with collagen fibrils in the subjacent compact layer and in the amnionic mesoderm. Light microscopically, bunches containing orcein-stained oxytalan and collagen-type-IV-immuno-stained microfibrils were seen rising from the amnionic mesoderm perpendicularly towards the epithelial layer, where they obviously inserted. It can be assumed that the subepithelial microfibrillar layer and the following compact layer form an anchoring zone between the amnionic mesoderm and the epithelium that may contribute to the maintenance of strength. The ultrastructure of the bunches clearly showed collagen fibrils mixed with oxytalan microfibrils. No collagen type I-immunostaining was found in the bunches. After pretreatment of cryostat sections with elastase, oxytalan-orcein-staining was absent, but collagen type IV-immunoreactivity was not altered. Furthermore, after oxytalan-orcein-staining resp. anti-collagen type IV incubation, all positive fibres revealed an identical morphological pattern. We propose that oxytalan and collagen type IV may represent further members of the microfibril complex.

Adult↗
PubMed1999

Expression of the beta3 tubulin gene (beta Tub60D) in the visceral mesoderm of Drosophila is dependent on a complex enhancer that binds Tinman and UBX.

The beta3 tubulin gene of Drosophila is expressed in the major mesodermal derivatives during their differentiation. The gene is subject to complex stage- and tissue-specific transcriptional control by upstream as well as downstream regions. Analysis of the vm1 enhancer, which is responsible for tissue-specific expression in the visceral mesoderm and is localized in the intron, revealed a complex modular arrangement of regulatory elements. In vitro and in vivo experiments uncovered two binding sites, termed UBX1 and UBX2, for the product of the homeotic gene Ultrabithorax (Ubx), which are required for high-level expression in pPS6 and PS7. Further analysis of the vm1 enhancer revealed that deletion of a specific element, termed element 7 (e7), abolishes transcription of the lacZ reporter gene in all parasegments except pPS6/PS7. Gel-retardation and footprint analysis identified a binding site for the homeodomain protein Tinman, which is essential for the specification of the dorsal mesoderm, within e7. Simultaneous deletion of two further sequence blocks in the vml enhancer, named elements 3 (e3), and 6 (e6), results in a reduction analogous to that caused by removal of e7. The e6 sequence contains conserved motifs also found in the visceral enhancer of the Ubx gene. Therefore we conclude that these elements act in concert with the Tinman binding site to achieve high expression levels. Thus the vm1 enhancer of the beta3 tubulin gene contains a complex array of elements that are involved in transactivation by a combination of tissue- and position-specific factors including Tinman and UBX.

Animals↗
PubMed1984

Differential contribution of dorsal and ventral lateral plate mesoderm to hemopoiesis during Rana pipiens embryogenesis.

Data obtained from studies on the origin and development of hemopoietic cells in several classes of vertebrate embryos argue for two distinct sources of hemopoietic cells, the intraembryonic dorsal lateral plate and the extraembryonic ventral blood island/yolk sac. In the present study, a stage by stage comparison of the hemopoietic potential of both of these regions was made during development of the frog, Rana pipiens. Either dorsal lateral plate or ventral blood island mesoderm was reciprocally transplanted between cytogenetically labeled triploid and diploid embryos. The ratio of donor-derived cells to host-derived cells (labeling index) was determined from Feulgen-stained DNA measurements of cells harvested from hemopoietic organs of young larvae. Blood island transplants consistently resulted in larvae with positive labeling of the circulating blood. Transplanted dorsal mesoderm supplied mesonephric granulocytes and thymocytes, but not circulating erythrocytes to larvae. However, the contribution of dorsal mesoderm to larval hemopoiesis fluctuated with respect to embryonic stage at transplantation.

Animals↗