Regulation of myogenesis by environmental hypoxia.

In aerobic organisms, oxygen is a critical factor for tissue and organ morphogenesis from embryonic development throughout the adult life. It regulates various intracellular pathways involved in cellular metabolism, proliferation, cell survival and fate. Organisms or tissues rapidly respond to changes in oxygen availability by activating complex signalling networks, which culminate in the control of mRNA translation and/or gene expression.

An adhesome comprising laminin, dystroglycan and myosin IIA is required during notochord development in Xenopus laevis.

Dystroglycan (Dg) is a transmembrane receptor for laminin that must be expressed at the right time and place in order to be involved in notochord morphogenesis. The function of Dg was examined in Xenopus laevis embryos by knockdown of Dg and overexpression and replacement of the endogenous Dg with a mutated form of the protein. This analysis revealed that Dg is required for correct laminin assembly, for cell polarization during mediolateral intercalation and for proper differentiation of vacuoles.

The dystroglycan: nestled in an adhesome during embryonic development.

Invertebrate and vertebrate development relies on complex processes that require many coordinated cell functions including cell adhesion, migration, proliferation and polarization. These processes depend on tissues and are spatio-temporally regulated by specific interactions between cells and between cells and the extracellular matrices. The dystroglycan, a transmembrane receptor that binds multiple extracellular matrix proteins, is expressed from oogenesis to organogenesis.

The translational repressor 4E-BP mediates hypoxia-induced defects in myotome cells.

Cell growth, proliferation, differentiation and survival are influenced by the availability of oxygen. The effect of hypoxia on embryonic cells and the underlying molecular mechanisms to maintain cellular viability are still poorly understood. In this study, we show that hypoxia during Xenopus embryogenesis rapidly leads to a significant developmental delay and to cell apoptosis after prolonged exposure.

Dystroglycan is involved in skin morphogenesis downstream of the Notch signaling pathway.

Dystroglycan (Dg) is a transmembrane protein involved both in the assembly and maintenance of basement membrane structures essential for tissue morphogenesis, and the transmission of signals across the plasma membrane. We used a morpholino knockdown approach to investigate the function of Dg during Xenopus laevis skin morphogenesis. The loss of Dg disrupts epidermal differentiation by affecting the intercalation of multiciliated cells, deposition of laminin, and organization of fibronectin in the extracellular matrix (ECM).

Blunting effect of hypoxia on the proliferation and differentiation of human primary and rat L6 myoblasts is not counteracted by Epo.

Objectives: The aim of this study was to evaluate whether hypoxia and/or erythropoietin would be able to modulate proliferation/differentiation processes of rat and human myoblasts.

Materials And Methods: Rat L6 and primary human myoblasts were grown in 21% or 1% O(2) in the presence or absence of recombinant human erythropoietin (RhEpo). Presence of erythropoietin receptors (EpoR) was assayed using RT-PCR and Western blotting techniques.

In vivo analyzes of dystroglycan function during somitogenesis in Xenopus laevis.

Dystroglycan (Dg) is a cell adhesion receptor for laminin that has been reported to play a role in skeletal muscle cell stability, cytoskeletal organization, cell polarity, and signaling. Here we show that Dg is expressed at both the notochord/somite and the intersomitic boundaries, where laminin and fibronectin are accumulated during somitogenesis. Inhibition of Dg function with morpholino antisense oligonucleotides or a dominant negative mutant results in the normal segmentation of the presomitic mesoderm but affects the number, the size, and the integrity of somites.

A function for dystroglycan in pronephros development in Xenopus laevis.

Dystroglycan (Dg) is a laminin receptor that is expressed at the interface between the basement membrane and the cell membrane. Dg has been reported to play a role in skeletal muscle cell stability, morphogenesis of neuroepithelial tissues, and in regulating cytoskeletal organization, cell polarization, and cell signalling. In this study, we have focused our analysis on the expression of Dg-mRNA and protein at different developmental stages in the pronephros of Xenopus laevis.

Integrin alpha3 subunit participates in myoblast adhesion and fusion in vitro.

Satellite cells are myogenic precursor cells, participating in growth, and regeneration of skeletal muscles. The proteins that play a role in myogenesis are integrins. In this report, we show that the integrin alpha3 subunit is expressed in quiescent satellite cells and activated myoblasts.

Cloning and expression patterns of dystroglycan during the early development of Xenopus laevis.

Dystroglycan is a cell surface receptor involved in the pathogenesis of muscular dystrophy, and plays a critical role in the assembly and homeostasis of basement membranes. Since data about the amphibian homologue are limited, we have cloned the full-length dystroglycan cDNAs from the frog Xenopus laevis. Using in situ hybridization, we show that mRNA expression is dynamic, particularly in the notochord at the end of gastrulation and during neurulation, suggesting that the protein might play unexplored roles in the specification and/or formation of this tissue.

ADAM13 disintegrin and cysteine-rich domains bind to the second heparin-binding domain of fibronectin.

ADAM13 is a member of the disintegrin and metalloprotease protein family that is expressed on cranial neural crest cells surface and is essential for their migration. ADAM13 is an active protease that can cleave fibronectin in vitro and remodel a fibronectin substrate in vivo. Using a recombinant secreted protein containing both disintegrin and cysteine-rich domains of ADAM13, we show that this "adhesive" region of the protein binds directly to fibronectin.

Xenopus ADAM 13 is a metalloprotease required for cranial neural crest-cell migration.

Background: Cranial neural-crest (CNC) cells originate from the lateral edge of the anterior neuroepithelium and migrate to form parts of the peripheral nervous system, muscles, cartilage, and bones of the face. Neural crest-cell migration involves the loss of adhesion from the surrounding neuroepithelium and a corresponding increase in cell adhesion to the extracellular matrix (ECM) present in migratory pathways. While proteolytic activity is likely to contribute to the regulation of neural crest-cell adhesion and migration, the role of a neural crest-specific protease in these processes has yet to be demonstrated.

PACSIN2 is a regulator of the metalloprotease/disintegrin ADAM13.

ADAM13 is a cell surface metalloprotease expressed in cephalic neural crest cells during early Xenopus development. The cytoplasmic domain of ADAM13 contains three potential SH3 (Src homology type 3) binding sites, suggesting that this region may support interactions with intracellular proteins. In this report we describe the identification, by a new strategy, of three proteins that bind the ADAM13 cytoplasmic domain in vitro: X-Src1, X-An4, and X-PACSIN2.

Heterotopic expression of the Xl-Fli transcription factor during Xenopus embryogenesis: modification of cell adhesion and engagement in the apoptotic pathway.

In the Xenopus laevis embryo, the overexpression of the Xl-FLI protein, a transcription factor of the ETS family, provokes severe developmental anomalies, which affect anteroposterior and dorsoventral polarities, optic cup formation, head cartilage morphogenesis, and erythrocyte differentiation. It has been proposed that these effects could be correlated to modifications of cell adhesion properties and/or to an increased engagement of cells in the apoptotic pathway during early development (Remy et al., Int.

Integrins: regulators of embryogenesis.

Integrins are heterodimeric transmembrane glycoproteins involved in cell-cell and cell-extracellular matrix adhesion. They also participate in cytoskeletal rearrangements, co-regulation of growth factor activities and activation of signal transductions. This review describes experimental approaches that have given new insights into the integrin functions during embryogenesis.

Fibronectin matrix composition and organization can regulate cell migration during amphibian development.

Fibronectin (FN) is an adhesive extracellular matrix component that is essential for vertebrate development. It forms a fibrillar matrix at the cell surface which controls cell morphology, migration, proliferation, and other important cellular processes. To address specific functions of FN matrix structure during early vertebrate development, we introduced normal and mutant recombinant FNs (recFNs) into the blastocoel cavity of embryos of the amphibian Pleurodeles waltl.

Relations between the stage of cell maturation and lactate transporter activities in rat neonatal muscle cells in culture.

Lactate transport was investigated in newborn rat muscle cells in culture. The aim was to study the lactate transport function at two stages of cell differentiation in culture: (i) during the proliferative phase characterized by myoblasts and myotubes (MyB/MyT2) obtained after 2-3 seedings, (ii) when myotubes (MyT1) grow old in culture after 8-9 seedings. In both developmental stages MyB/MyT2, lactate was carried following a saturable and sigmoidal velocity curve: the Hill and the Scatchard plot analyses confirmed an allosteric or multisite mechanism of lactate transport with two classes of carriers: one of low and one of high affinity i.

A key function for alphav containing integrins in mesodermal cell migration during Pleurodeles waltl gastrulation.

During cleavage of Pleurodeles waltl amphibian embryos, inner cells of the blastocoel roof (presumptive ectodermal and mesodermal cells) organize a fibrillar extracellular matrix (ECM) containing fibronectin on their basal surface by a beta1-integrin-dependent process. This matrix is used as a migratory substrate by mesodermal cells during gastrulation. While alpha5beta1 integrin is expressed on both ectodermal and mesodermal cell surface, we have shown previously that alphav containing integrins are essentially restricted to the surface of mesodermal cells (Alfandari, D.

What mechanisms drive cell migration and cell interactions in Pleurodeles?

Embryogenesis implies a strict control of cell interaction and cell migration. The spatial and temporal regulation of morphogenetic movements occurring during gastrulation is directly dependent on the early cell interactions that take place in the blastula. The newt Pleurodeles waltl is a favorable model for the study of these early morphogenetic events.

The RGD-dependent and the Hep II binding domains of fibronectin govern the adhesive behaviors of amphibian embryonic cells.

In early amphibian development, interactions between fibronectin and both ectoderm and mesoderm cells are critical in the progression of gastrulation movements. In the Pleurodeles waltl embryo, it has been established that ectoderm cells of the animal hemisphere organize a fibrillar-extracellular matrix containing fibronectin. Mesoderm cells migrate along the blastocoel roof using these fibronectin fibrils as substratum.

Integrin alpha v subunit is expressed on mesodermal cell surfaces during amphibian gastrulation.

Mesodermal cell migration during amphibian gastrulation is dependent on cellular interactions with fibronectin. One mechanism whereby cells bind fibronectin is through alpha v-containing integrin heterodimers. In order to investigate the role of alpha v in amphibian gastrulation, we have cloned the Pleurodeles homologue of the integrin alpha v subunit using homology PCR.

Mesodermal cell adhesion to fibronectin-rich fibrillar extracellular matrix is required for normal Rana pipiens gastrulation.

New observations on thin strips of cells from the leading edge of the involuting presumptive mesoderm explanted onto FN-coated substrate show a striking preferential cellular emigration from the leading edge of explants. Microinjected probes (Fab' anti-FN, Fab' anti-integrin and RGD-peptides) that disrupt cell adhesion to the FN-matrix on basal surface of the blastocoel roof also disrupt normal anuran gastrulation, producing blocked embryos with no adhesion of leading edge mesodermal cells to the blastocoel roof, abnormal epiboly, and defects of mesodermal cell spreading across the basal surface of the blastocoel roof toward the animal pole. These results show that the FN-rich fibrillar extracellular matrix on the basal surface of the blastocoel roof is required for normal gastrulation in Rana pipiens embryos.

Distinct regions of human fibronectin are essential for fibril assembly in an in vivo developing system.

In early vertebrate development, the proper assembly of fibronectin into fibrils is crucial for embryonic cells to adhere and to migrate on the extracellular matrix. The molecular mechanisms by which such a process occurs in vivo are poorly understood. In the amphibian embryo Pleurodeles waltl fibronectin fibrils appear first at the blastula stage.

Ambystoma maculatum gastrulae have an oriented, fibronectin-containing extracellular matrix.

During early development of the urodele Ambystoma maculatum, the appearance and distribution of fibronectin-containing fibrillar extracellular materials were studied by immunocytochemistry. Fibronectin (FN) first appears in the early blastula (stage 7) as thin punctate fibrils on the cell surface concentrated in the marginal zone. In late blastula (stage 9), thin fibrils are found throughout the blastocoel roof.