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Failure of egg cylinder elongation and mesoderm induction in mouse embryos lacking the tumor suppressor smad2
1Laboratory of Biochemistry and Metabolism, National Institute of Diabetes and Digestive and Kidney Diseases, 10/9N105, 10 Center Drive, National Institutes of Health, Bethesda, MD 20892, USA.
Abstract:
smad genes constitute a family of nine members whose products serve as intracellular mediators of transforming growth factor beta signals. SMAD2, which is a tumor suppressor involved in colorectal and lung cancer, has been shown to induce dorsal mesoderm in Xenopus laevis in response to transforming growth factor beta and activins. The smad2 gene is expressed ubiquitously during murine embryogenesis and in many adult mouse tissues. Animals that lacked smad2 died before 8.5 days of development (E8.5). E6.5 homozygous mutants were smaller than controls, lacked the extraembryonic portion of the egg cylinder, and appeared strikingly similar to E6.5 smad4 mutants. This similarity was no longer evident at E7.5, however, because the smad2 mutants contained embryonic ectoderm within their interiors. Molecular analysis showed that smad2 mutant embryos did not undergo gastrulation or make mesoderm. The results demonstrate that smad2 is required for egg cylinder elongation, gastrulation, and mesoderm induction.
Insights
The smad2 gene is crucial for early mouse development, regulating gastrulation and mesoderm formation. Its absence leads to developmental failure before embryonic day 8.5.
Area of Science:
- Developmental Biology
- Molecular Biology
- Genetics
Background:
- Smad proteins are key intracellular mediators of transforming growth factor beta (TGF-β) signaling.
- SMAD2 is a tumor suppressor implicated in colorectal and lung cancers.
- SMAD2 induces dorsal mesoderm in Xenopus laevis.
Purpose of the Study:
- To investigate the role of the smad2 gene during early murine embryogenesis.
- To determine the consequences of smad2 gene loss on embryonic development.
Main Methods:
- Analysis of smad2 homozygous mutant mice at various embryonic stages (E6.5, E7.5, E8.5).
- Phenotypic characterization of mutant embryos.
- Molecular analysis of gastrulation and mesoderm induction in mutants.
Main Results:
- smad2 homozygous mutants exhibited developmental arrest before E8.5.
- At E6.5, mutants were smaller and lacked the extraembryonic portion of the egg cylinder, resembling smad4 mutants.
- At E7.5, smad2 mutants showed internal embryonic ectoderm, indicating a failure in gastrulation and mesoderm formation.
Conclusions:
- smad2 is essential for egg cylinder elongation, gastrulation, and mesoderm induction in mouse embryos.
- Loss of smad2 function severely disrupts early embryonic patterning and development.
- These findings highlight the critical role of smad2 in TGF-β pathway-mediated developmental processes.
