title: Apoptosis of tail muscle during amphibian metamorphosis involves a caspase 9-dependent mechanism.
abstract: The climax of amphibian metamorphosis is marked by thyroid hormone-dependent tadpole tail resorption, implicating apoptosis of multiple cell types, including epidermal cells, fibroblasts, nerve cells, and muscles. The molecular cascades leading to and coordinating the death of different cell types are not fully elucidated. It is known that the mitochondrial pathway, and in particular the Bax and XR11 genes, regulates the balance between apoptosis and survival in muscle. However, the down-stream factors modulated by changes in mitochondrial permeability have not been studied in a functional context. To investigate further the mitochondrial-dependent pathway, we analyzed the regulation and the role of caspase 9 in Xenopus tadpoles. We report that caspase 9 mRNA is expressed in the tail before metamorphosis and increases before and during climax. Similarly, at the protein level, the production of active forms of caspase 9 increases in muscle tissue as metamorphosis progresses. To assess the functional role of caspase 9, we designed a dominant-negative protein. Overexpression of this dominant-negative abrogates both Bax-induced cell death in vitro and muscle apoptosis in vivo during natural metamorphosis. These findings consolidate a model of metamorphic muscle death that directly implicates the mitochondrial pathway and the apoptosome.
authors.affiliation: Evolution des Régulations Endocriniennes, Muséum National d'Histoire Naturelle, UMR-CNRS 5166, Paris, France.
authors.forename: Isaline
authors.initials: I
authors.lastname: Rowe
authors.forename: Karine
authors.initials: K
authors.lastname: Le Blay
authors.forename: David
authors.initials: D
authors.lastname: Du Pasquier
authors.forename: Karima
authors.initials: K
authors.lastname: Palmier
authors.forename: Giovanni
authors.initials: G
authors.lastname: Levi
authors.forename: Barbara
authors.initials: B
authors.lastname: Demeneix
authors.forename: Laurent
authors.initials: L
authors.lastname: Coen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology*; D053453:Caspase 9; D020169:Caspases / Q000235:genetics / Q000502:physiology*; D018014:Gene Transfer Techniques; D007814:Larva / Q000254:growth & development; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000502:physiology*; D009154:Mutation; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D013623:Tail / Q000502:physiology*; D014981:Xenopus; D051028:bcl-2-Associated X Protein
chemical_list: D019253:Proto-Oncogene Proteins c-bcl-2; D011993:Recombinant Fusion Proteins; D051028:bcl-2-Associated X Protein; D053453:Caspase 9; D020169:Caspases