Biomedical subjects

J F Riou

Publications and source records attributed to J F Riou.

At least 55 records · Page 3Linked to original sources

PubMed1997

Copper-dependent oxidative and topoisomerase II-mediated DNA cleavage by a netropsin/4'-(9-acridinylamino)methanesulfon-m-anisidide combilexin.

A conjugate molecule was synthesized by linking the DNA-intercalative antitumor drug 4'-(9-acridinylamino)methanesulfon-manisidide (mAMSA) via a 4-carboxamide side chain to a dipyrrolecarboxamide moiety structurally related to the minor groove-binding antibiotic netropsin. The molecule (netropsin/ mAMSA) behaves as a threading intercalator. Its netropsin-like tail becomes located in the minor groove of the double helix and serves to drive the hybrid molecule preferentially to AT-rich sites on various DNA fragments as revealed by DNase I footprinting. The hybrid retains the susceptibility to copper-dependent oxidation characteristic of the parent mAMSA moiety as well as its ability to generate oxygen radicals, which can mediate DNA damage, mainly at cytidine and guanosine nucleotides. It also retains the property of stimulating the formation of cleavable complexes with DNA in the presence of topoisomerase II, but its netropsin-like moiety confers little or no influence on the reaction with topoisomerase I. Although netropsin/mAMSA is less potent than mAMSA at producing cleavable complexes with topoisomerase II, it promotes the appearance of cleavage sites at much the same nucleotide sequences as does the parent compound. The dipyrrolecarboxamide tail is not silent, however, since it modifies the concentration-dependence of cleavable complex formation.

Amsacrine↗

PubMed1996

Intracellular molecular interactions of antitumor drug amsacrine (m-AMSA) as revealed by surface-enhanced Raman spectroscopy.

Cytotoxicity of several classes of antitumor DNA intercalators is thought to result from disturbance of DNA metabolism following trapping of the nuclear enzyme DNA topoisomerase II as a covalent complex on DNA. Here, molecular interactions of the potent antitumor drug amsacrine (m-AMSA), an inhibitor of topoisomerase II, within living K562 cancer cells have been studied using surface-enhanced Raman (SER) spectroscopy. The work is based on data of the previously performed model SER experiments dealing with amsacrine/DNA, drug/topoisomerase II and drug/DNA/topoisomerase II complexes in aqueous buffer solutions. The SER data indicated two kinds of amsacrine interactions in the model complexes with topoisomerase II alone or within ternary complex: non-specific (via the acridine moiety) and specific to the enzyme conformation (via the side chain of the drug). These two types of interactions have been both revealed by the micro-SER spectra of amsacrine within living K562 cancer cells. Our data suppose the specific interactions of amsacrine with topoisomerase II via the side chain of the drug (particular feature of the drug/topoisomerase II and ternary complexes) to be crucial for its inhibitory activity.

Amsacrine↗

PubMed1996

DNA topoisomerase I changes the mode of interaction between camptothecin drugs and DNA as probed by UV-resonance Raman spectroscopy.

Pronounced differences of interactions of camptothecin (CPT) and its derivative 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT11), inhibitors of DNA topoisomerase I, with oligonucleotides were found using UV resonance Raman spectroscopy. 30-mer oligonucleotides were derived from the sequences of the topoisomerase I-induced and CPT-enhanced cleavage sites in SV40 DNA. CPT induces well-defined alterations of the oligo structure, whereas CPT11 interacts with oligonucleotides more weakly and in another manner than CPT. Formation of cleavable ternary complexes between CPT11, topoisomerase I and oligonucleotides causes CPT11 to interact with oligonucleotides in the same fashion as was found for its parent compound CPT, and enhances this interaction as compared to CPT-oligonucleotide complexes. The data present evidence of molecular interactions of CPT11 with both other partners (topoisomerase I and oligonucleotide) of the ternary cleavable complex at the oligonucleotide-enzyme interface.

Antineoplastic Agents, Phytogenic↗

PubMed1996

Structure-activity relationships in a series of substituted indolocarbazoles: topoisomerase I and protein kinase C inhibition and antitumoral and antimicrobial properties.

A series of compounds structurally related to staurosporine, rebeccamycin, and corresponding aglycones was synthesized, and their activities toward protein kinase C and topoisomerases I and II were tested together with their in vitro antitumor efficiency against murine B16 melanoma and P388 leukemia cells. Their antimicrobial activities were also examined against a Gram-negative bacterium (Escherichia coli), a yeast (Candida albicans), and three Gram-positive bacteria (Bacillus cereus, Streptomyces chartreusis, and Streptomyces griseus). To avoid side effects expected with protein kinase C inhibitors, we introduced substitution on the maleimide nitrogen and/or a sugar moiety linked to one of the indole nitrogens to obtain specific inhibitors of topoisomerase I with minimal activities on protein kinase C. As expected, these structures were inefficient on topoisomerase II, and some of them exhibited a strong activity against topoisomerase I. Generally, dechlorinated compounds were found to be more active than chlorinated analogues against both purified topoisomerase I and protein kinase C. On the other hand, opposite results were obtained in the cell antiproliferative assays. These results suggest lack of cell membrane permeability in the absence of the chlorine residue or cleavage of carbon-chlorine bonds inside the cell.

Animals↗

PubMed1996

Identification and properties of a major plasma metabolite of irinotecan (CPT-11) isolated from the plasma of patients.

Irinotecan [7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT-11)] is a promising water-soluble analogue of camptothecin [S. Sawada et al., Chem. & Pharm. Bull. (Tokyo), 39: 1446-1454, 1991]. We have reported previously the presence of an important polar metabolite, in addition to 7-ethyl-10-hydroxycamptothecin (SN-38) beta-glucuronide, in samples of plasma taken from patients undergoing treatment with CPT-11 (L.P. Rivory and J. Robert, Cancer Chemother. Pharmacol. 36: 176-179, 1995; L. P. Rivory and J. Robert, J. Cromatogr., 661: 133-141, 1994). Plasma samples (0.5 ml) containing comparatively large amounts of this metabolite were extracted by solid-phase columns and subjected to high-performance liquid chromatography and mass spectrometry in parallel to fluorometric detection. The metabolite yielded [M + 1] ions with a m/z of 619, representing the addition of 32 atomic mass units to CPT-11. Purified fractions were subjected to proton nuclear magnetic resonance, and the structure determined, 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]carbonyloxycampothecin (APC), was further validated following synthesis. Like CPT-11, APC was found to be only a weak inhibitor of the cell growth of KB cells in culture (IC50, 2.1 versus 5.5 micrograms/ml for CPT-11 and 0.01 microgram/ml for SN-38, the active metabolite of CPT-11) and was a poor inducer of topoisomerase I DNA-cleavable complexes (100-fold less potent than SN-38). In contrast to CPT-11, APC was not hydrolyzed to SN-38 by human liver microsomes or purified human liver carboxylesterase. Furthermore, APC did not inhibit the hydrolysis of CPT-11 in these preparations. Interestingly, APC was only a weak inhibitor of acetylcholinesterase in comparison to CPT-11 and neostigmine. It appears likely, therefore, that APC does not contribute directly to the activity and toxicity profile of CPT-11 in vivo.

Antineoplastic Agents, Phytogenic↗

PubMed1996

Modulation of DNA topoisomerase I activity by p53.

The tumor suppressor protein p53 plays a central role in the cellular response to genotoxic lesions and has been shown to be activated by most anticancer agents such as mitomycin C. We here show that mitomycin C treatment of human MCF7 breast adenocarcinoma cells results in increased topoisomerase I activity as measured by relaxation of supercoiled DNA and by phosphorylation of SR protein splicing factor. The increase in catalytic activity occurs in parallel with the nuclear accumulation of p53, resulting in detectable activation of topoisomerase I within less than 1 h of drug treatment. Furthermore, topoisomerase I co-immunoprecipitates with nuclear p53, suggesting that the activation of topoisomerase I may be a result of a direct interaction between the two proteins. In vitro experiments with purified recombinant proteins show that p53 increases the catalytic activities of topoisomerase I as measured by relaxation of supercoiled DNA, stabilization of the covalent topoisomerase I-DNA complex (in the presence of camptothecin), and phosphorylation of SR protein splicing factor ASF/SF2. Furthermore, topoisomerase I sediments at a higher molecular weight in the presence of p53 as revealed by sucrose density gradient analysis in the absence of DNA. Finally, p53 modifies the thermal stability of topoisomerase I, protecting it from heat denaturation. Taken together, our results show that topoisomerase I and p53 form molecular complexes in vitro as in vivo, and we suggest that the p53-mediated response to DNA damage may, at least in part, involve activation of topoisomerase I.

Animals↗

PubMed1996

Specific phosphorylation of SR proteins by mammalian DNA topoisomerase I.

Several metazoan splicing factors are characterized by ribonucleoprotein (RNP) consensus sequences and arginine-serine repeats (RS domain) which are essential for their function in splicing. These include members of the SR-protein family (SC35, SF2/ASF), the U1 small nuclear (sn) RNP protein (U1-70K) and the U2 snRNP auxiliary factor (U2AF). SR proteins are phosphorylated in vivo and the phosphorylation state of U1-70K's RS domain influences its splicing activity. Here we report the purification of a protein kinase that is specific for SR proteins and show that it is DNA topoisomerase I. This enzyme lacks a canonical ATP-binding motif but binds ATP with a dissociation constant of 50 nM. Camptothecin and derivatives, known to be specific inhibitors of DNA topoisomerase I, strongly inhibit the kinase activity in the presence of DNA and affect the phosphorylation state of SR proteins. Thus, DNA topoisomerase I may well be one of the SR protein kinases operating in vivo.

Adenosine Triphosphate↗

PubMed1996

Early regionalized expression of a novel Xenopus fibroblast growth factor receptor in neuroepithelium.

A cDNA encoding a novel Xenopus fibroblast growth factor receptor, XFGFR4B, has been cloned. XFGFR4B mRNA is detected throughout embryogenesis. However, from the late gastrula stage on, XFGFR4B transcripts are expressed in two defined areas of the anterior neural plate. Interestingly, these two regions are fated to become parts of the retina, midbrain, hindbrain, and otic vesicle, all of which continue to express XFGFR4B mRNA in tailbud stage embryos and early tadpoles. Expression of XFGFR4B mRNA can be maintained at neurula stage in isolated blastula ectoderm in response to mesodermal induction by activin or neural induction by noggin, suggesting that XFGFR4B expression might be regulated by early cell interactions. Distribution of XFGFR4B mRNA suggests that XFGFR4B might serve an important function during patterning of neuroepithelium.

Amino Acid Sequence↗

PubMed1996

From amsacrine to DACA (N-[2-(dimethylamino)ethyl]acridine-4-carboxamide): selectivity for topoisomerases I and II among acridine derivatives.

A number of acridine derivatives, including the clinical antileukaemia agent amsacrine and the experimental agent DACA (N-[2-(dimethylamino)ethyl]acridine-4-carboxamide), target the enzyme topoisomerase II. We demonstrate here that DACA induces DNA cleavage in the presence of topoisomerase I as well as of topoisomerase II. We also investigate a series of acridine derivatives which link amsacrine to DACA in terms of DNA binding, topoisomerase poisoning and biological activity. The presence of an acridine 4-linked N-2-(dimethylamino)ethyl group provides both a pronounced G-C preference for DNA binding and activity towards topoisomerase I. The removal of the anilino side chain of amsacrine, in combination with the presence of the N-2-(dimethylamino)ethyl group, provides in vitro biological activity against "atypical" multidrug resistant leukaemia lines with low topoisomerase II activity. Among these compounds, suppression of the ionisation of the acridine nitrogen to produce the compound DACA is associated with experimental activity against solid tumours. The addition of an acridine 2-chloro substituent to DACA suppresses the stimulation of topoisomerase II-dependent DNA cleavage but increases stimulation of topoisomerase I cleavage. 2-Substitution also increases activity against the "atypical" multidrug resistant cell lines. Overall, the results suggest that augmentation of topoisomerase I-dependent activity in this series by appropriate chemical substitution in this series leads to circumvention of topoisomerase II-mediated multidrug resistance.

Acridines↗

PubMed1996

Salen-anthraquinone conjugates. Synthesis, DNA-binding and cleaving properties, effects on topoisomerases and cytotoxicity.

A series of amidoethylamino-anthraquinone derivatives bearing either one or two salen (bis(salicylidene)ethylenediamine) moieties complexed with CuII or NiII have been synthesized, and their DNA-binding and cleaving properties examined. The effects of the mono- and di-substituted anthracenedione-salen conjugates on DNA cleavage mediated by topoisomerases I and II have also been determined, as well as their cytotoxicity toward human KB cells. The anthraquinone-salen. NiII conjugates bind to GC-rich sequences in DNA, but do not cleave the macromolecule. By contrast, the anthraquinone-salen. CuII hybrids do not recognize particular nucleotide sequences but efficiently induce single-strand breaks in DNA after activation. The 5,8-dihydroxy-anthraquinone conjugates are more cytotoxic and more potent toward topoisomerase II than the non-hydroxylated analogues, but they are less cytotoxic than the salen-free anthraquinones. The attachment of a salen. CuII complex to the anthraquinone chromophore can confer DNA cleaving properties in vitro, but this is at the expense of cytotoxic activity. Anthraquinone-salen. CuII complexes may find useful employ as footprinting probes for investigating ligand-DNA interactions.

Anthraquinones↗

PubMed1996

Preclinical evaluation of CPT-11 and its active metabolite SN-38.

CPT-11 (irinotecan) is a water-soluble analogue of camptothecin (CPT), an antitumor drug extracted from the Chinese tree Camptotheca acuminata. SN-38 is an active metabolite of CPT-11 that contributes significantly to its activity. The antitumor effects of CPT-11 and SN-38 are exerted through a novel mechanism of action; inhibition of DNA topoisomerase I. CPT-11 and its metabolite have demonstrated potent inhibitory activity against a variety of cancer cell lines in vitro and against several murine and human tumors grafted in mice in vivo, including those that express multidrug resistance. CPT-11 has also shown synergistic activity in combination with 5-fluorouracil and cisplatin in vitro. No irreversible or unusual toxicities were observed with CPT-11 in animal toxicity studies. In summary, the preclinical profile of CPT-11 confirmed this drug to be an attractive candidate for clinical development.

Animals↗

PubMed1996

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 combination of orthotopic grafting and fluorescent lineage tracers has led to precise early gastrula mesoderm fate maps. It is now clear that there are no sharp boundaries between germ layers at the onset of gastrulation but rather diffuse transition zones. The coordination of cell movements during gastrulation is closely related to the establishment of dorsoventral polarity. Ventralization by U.V. irradiation or dorsalization by lithium treatment modifies the capacity for autonomous migration on the fibronectin coated substratum of marginal zone cells accordingly. It is now firmly established that mesodermal cells need to adhere to a fibrillar extracellular matrix (ECM) to undergo migration during gastrulation. Extracellular fibrils contain laminin and fibronectin (FN). Interaction of cells with ECM involves receptors of the beta 1 integrin family. A Pleurodeles homolog of the alpha v integrin subunit has been recently identified. Protein alpha v expression is restricted to the surface of mesodermal cells during gastrulation. Integrin-mediated interactions of cells with FN are essential for ECM assembly and mesodermal cell migration. Intracellular injection of antibodies to the cytoplasmic domain of beta 1 into early cleavage embryos causes inhibition of FN fibril formation. Intrablastocoelic injections of several probes including antibodies to FN or integrin alpha 5 beta 1, competitive peptides to the major cell binding site of FN or the antiadhesive protein tenascin all block mesodermal cell migration. This results in a complete arrest of gastrulation indicating that mesodermal cell migration is a major driving force in urodele gastrulation. It is now possible to approach the role of fibroblast growth factor (FGF) during cell interactions taking place in urodele embryos. Four different FGF receptors (FGFR) have been cloned in Pleurodeles. Each of them has a unique mRNA expression pattern. FGFR-1, FGFR-3, and the variant of FGFR-2 containing the IIIb exon are maternally expressed and might be involved in mesodermal induction. During gastrulation, FGFR-3 and FGFR-4 have a restricted pattern of expression, whereas FGFR-1 mRNA is nearly uniformly distributed. Splicing variants FGFR-2IIIb and FGFR-2IIIc have exclusive expression patterns during neurulation. IIIb is expressed in epidermis and IIIc in neural tissue, suggesting a function in the differentiation of ectodermal derivatives.

Animals↗

PubMed1995

Effects of two distamycin-ellipticine hybrid molecules on topoisomerase I and II mediated DNA cleavage: relation to cytotoxicity.

Two distamycin-ellipticine conjugates were examined for their ability to modulate topoisomerase I and topoisomerase II-DNA cleavable complex formation in vitro. Hybrid molecules Distel (1+) and Distel (2+) both contain a DNA-intercalating chromophore and a tris-pyrrole element capable of binding within the minor groove of DNA. The two drugs differ only in the nature of the side chain attached to the distamycin moiety. The monocationic hybrid Distel (1+) is a dual topoisomerase I and II inhibitor with characteristics differing from those of the parent compounds distamycin and ellipticine. By contrast, the biscationic hybrid Distel (2+) exerts no significant effects on either topoisomerase I or II. The cytotoxic properties of the two drugs towards P388 leukaemic cells sensitive and resistant to camptothecin correlate with topoisomerase inhibitory properties but not with DNA-binding properties.

Animals↗

PubMed1995

Preclinical evaluation of docetaxel (Taxotere).

Progress in cancer chemotherapy has been made owing to the discovery and development of drugs that have new structures, new mechanisms of action, and high levels of experimental antitumor activity. Docetaxel (Taxotere; Rhône-Poulenc Rorer, Antony, France) is prepared by semisynthesis from 10-deacetyl baccatin III, an inactive taxoid precursor extracted from the needles of the European yew Taxus baccata. Docetaxel has been found to promote tubulin assembly in microtubules and to inhibit their depolymerization. As predicted by its unique biochemical mechanism of action, docetaxel acts as a mitotic spindle poison and induces a mitotic block in proliferating cells. In vitro, the docetaxel concentrations required to reduce murine and human cell survival by 50% range from 4 to 35 ng/mL, and the cytotoxic effects are greater on proliferating cells than on nonproliferating cells. Docetaxel also is cytotoxic at clinically relevant concentrations against fresh human tumor biopsy specimens (breast, lung, ovarian, colorectal cancer, melanoma) in a soft agar cloning system. Docetaxel has significant in vivo antitumor activity in the different models generally used for the preclinical evaluation of drugs. Eleven of 12 murine transplantable tumors in syngeneic mice have been found to be sensitive to intravenous docetaxel with complete regressions of advanced-stage tumors. Activity also has been observed with human tumor xenografts in nude mice at an advanced stage. In combination studies, synergism has been observed in vivo with 5-fluorouracil, cyclophosphamide, etoposide, vinorelbine, and methotrexate. Preclinical toxicity in mice and dogs has been evaluated by using one and five daily intravenous doses, respectively. The dog was found to be the more sensitive species. The dose-limiting toxicities are hematologic and gastrointestinal in both species. Neurotoxicity also has been observed at high dosages in mice.

Animals↗

PubMed1995

Synthesis and biological evaluation of amino-substituted benzo[f]pyrido[4,3-b] and pyrido[3,4-b]quinoxalines: a new class of antineoplastic agents.

In order to study the structure-activity relationships in the series of new intercalating polycyclic agents, 1-amino-substituted pyrido[3,4-b]quinoxalines, benzo[f]pyrido[4,3-b]quinoxaline derivatives bearing a dibasic side chain and their benzo[f]pyrido[3,4-b] isomers have been synthesized. Biological evaluation was carried out for topoisomerase I and II inhibition, and for in vitro and in vivo antitumor properties in several models. Results demonstrate that appropriately substituted benzo[f]pyrido[4,3-b]quinoxaline derivatives are inhibitors of topoisomerase I and II, and have significant antitumor properties in various experimental models. In addition, the most active compounds appear to be minimally recognized by tumor cells expressing the multidrug resistance phenotype.

Animals↗

PubMed1994

Synthesis and structure-activity relationships of new antitumor taxoids. Effects of cyclohexyl substitution at the C-3' and/or C-2 of taxotere (docetaxel).

Synthesis and cytotoxicity of the new analogs (11-13) of docetaxel possessing cyclohexyl groups instead of phenyl groups at the C-3' and/or C-2 benzoate positions are described. The C-2 cyclohexanecarboxylate analog of paclitaxel (15) is also synthesized for comparison. The potency of these new taxoids were examined for their inhibitory activity for microtubule disassembly and also for their cytotoxicity against murine P388 leukemia cell line as well as doxorubicin-resistant P388 leukemia cell line (P388/Dox). It is found that 3'-dephenyl-3'-cyclohexyldocetaxel (11) (0.72T) and 2-(hexahydro)docetaxel (12) (0.85T) possess strong inhibitory activity for microtubule disassembly equivalent to docetaxel (0.7T), which is more potent than paclitaxel (1.0T). The results clearly indicate that phenyl or an aromatic group at C-3' or C-2 is not a requisite for strong binding to the microtubules. This finding has opened an avenue for development of new nonaromatic analogs of docetaxel and paclitaxel. 3'-Dephenyl-3'-cyclohexyl-2-(hexahydro)docetaxel (13) (2T) turns out to be a substantially weaker inhibitor. The cytotoxicities of 11-13 against P388 are, however, in the same range that is 8-12 times weaker than docetaxel and 4-6 times weaker than paclitaxel, i.e., 13 shows equivalent cytotoxicity to that of 11 or 12 in spite of much lower microtubule disassembly inhibitory activity. The cytotoxicities of these new taxoids against the P388/Dox cell line are only 2-2.5 times lower than that of docetaxel. The potency of 2-(hexahydro)paclitaxel (15) for these assays is much lower than the docetaxel counterpart 12. The significant loss of activity in vivo against B16 melanoma is observed for 11-13, i.e., 11 is only marginal (T/C = 38% at 20 mg/kg/day), and 12 and 13 are inactive (T/C = 76% and 79%, respectively). This could be ascribed to faster metabolism, faster excretion or other bioavailability problems.

Animals↗

PubMed1994

Molecular interactions of DNA-topoisomerase I and II inhibitor with DNA and topoisomerases and in ternary complexes: binding modes and biological effects for intoplicine derivatives.

Molecular interactions of intoplicine, dual DNA-topoisomerases (Topo) I and II inhibitor, with topoisomerases, plasmid DNA, in ternary cleavable complexes with enzymes and plasmid DNA, and in the reversed cleavable complexes were examined by means of surface-enhanced Raman scattering (SERS) and CD spectroscopy and by biochemical techniques. Detailed spectral analysis of intoplicine derivatives allowed us to assign SERS vibrational modes of chromophores and to propose the models for these complexes. Intoplicine was found to be able to interact specifically with the Topo II alone, but with Topo I only when in the presence of DNA. It shows at least two modes of binding to the DNA: the first was found to be dominant for its derivative 1c (most potent Topo I inhibitor), and the second was dominant for derivative 2a (most potent Topo II inhibitor). The possibility of forming these two types of complexes simultaneously is suggested to be one of the main factors enabling the drug to be a dual Topo I and Topo II inhibitor. The "deep intercalation mode" of the drug from the DNA minor groove with the long axis of the chromophore oriented roughly parallel to the dyad axis has been suggested to be responsible for induction of distortions of the DNA structure by the intercalating drug. Being involved in the formation of Topo I-mediated cleavable ternary complex, the molecules participating in the deep intercalation mode within the DNA do not change their molecular interactions as compared with their complex with the DNA alone. The stabilization of the Topo I-mediated cleavable complex was shown to be followed by the local denaturation of DNA in the AT-rich regions of the helix. When the ternary cleavable complex was reversed, the drug was shown to be in the complex with the plasmid. The "outside binding mode" from the DNA major groove via the hydroxyl group of the A-ring of the chromophore has been suggested to be responsible for Topo II inhibition. These molecules did not induce significant distortions of the DNA structure. Being involved in the formation of Topo II-mediated cleavable ternary complex, the drug changed its molecular interactions as compared with the complex with DNA alone.(ABSTRACT TRUNCATED AT 400 WORDS)

Binding Sites↗

PubMed1994

Control of somitic expression of tenascin in Xenopus embryos by myogenic factors and Brachyury.

Tenascin is a large glycoprotein which is expressed in a restricted pattern in the extracellular matrix (ECM) of vertebrate embryos. Tenascin interferes with cell-fibronectin interactions in vitro, and may play a role in the control of cell migration and differentiation during development. In Xenopus, tenascin immunoreactivity is first detected at the early tailbud stage in the ECM of the most anterior somite. Thereafter, it is distributed dorsally along neural crest cell migration pathways. In this paper, we report that tenascin mRNA is most abundant in dorsal mesoderm at the neurula stage and in somites at the early tailbud stage, indicating that the initial accumulation of tenascin in the ECM is due to secretion from paraxial mesoderm. To understand how tenascin expression in somitic mesoderm is controlled, we have expressed Xbra and the myogenic factors XMyoD and XMyf5 in blastula animal cap tissue. The tenascin gene is activated by all three transcription factors. Interestingly, expression of tenascin mRNA, and accumulation of the protein in the ECM, can occur without formation of muscle. Our results suggest that tenascin regionalization in early Xenopus embryos depends on tenascin RNA expression by somitic mesoderm, where it is likely to be activated by myogenic factors.

Animals↗