Apoptosis of tail muscle during amphibian metamorphosis involves a caspase 9-dependent mechanism
Isaline Rowe1, Karine Le Blay, David Du Pasquier
1Evolution des Régulations Endocriniennes, Muséum National d'Histoire Naturelle, UMR-CNRS 5166, Paris, France.
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.
Insights
Thyroid hormone triggers tadpole tail resorption via apoptosis. Caspase 9 (a key protein) is crucial for muscle cell death during amphibian metamorphosis, involving the mitochondrial pathway.
Area of Science:
- Developmental Biology
- Cellular Biology
- Molecular Biology
Background:
- Amphibian metamorphosis involves tadpole tail resorption, a process driven by thyroid hormone and apoptosis.
- The molecular mechanisms coordinating cell death during metamorphosis are not fully understood.
- The mitochondrial pathway, involving genes like Bax, is known to regulate muscle cell apoptosis.
Purpose of the Study:
- To investigate the regulation and functional role of caspase 9 in the mitochondrial-dependent apoptosis pathway during Xenopus tadpole metamorphosis.
- To elucidate downstream factors modulated by mitochondrial permeability changes in metamorphic muscle death.
Main Methods:
- Analysis of caspase 9 mRNA expression in tadpole tails before and during metamorphosis.
- Quantification of active caspase 9 protein levels in muscle tissue.
- In vitro and in vivo functional studies using a dominant-negative caspase 9 protein to inhibit apoptosis.
Main Results:
- Caspase 9 mRNA expression increases in the tail prior to and during climax.
- Active caspase 9 protein levels rise in muscle tissue as metamorphosis progresses.
- Overexpression of dominant-negative caspase 9 inhibits Bax-induced cell death and muscle apoptosis during metamorphosis.
Conclusions:
- Caspase 9 is a key regulator of muscle apoptosis during amphibian metamorphosis.
- The findings support a model where the mitochondrial pathway and the apoptosome are directly involved in metamorphic muscle cell death.
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