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Anterior visceral endoderm SMAD4 signaling specifies anterior embryonic patterning and head induction in mice

Cuiling Li1, Yi-Ping Li, Xin-Yuan Fu

  • 1Mammalian Genetics Section, Genetics of Development and Disease Branch, National Institutes of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, 10/9N105, 10 Center Drive, Bethesda, MD 20892, USA.

International Journal of Biological Sciences
|October 14, 2010
PubMed

Insights

SMAD4 is crucial for early embryonic development. Its absence in the visceral endoderm prevents head formation, while epiblast SMAD4 is vital for later patterning, not initial mesoderm induction.

Area of Science:

  • Developmental Biology
  • Molecular Biology
  • Genetics

Background:

  • SMAD4 mediates transforming growth factor-beta (TGF-β) superfamily signaling.
  • SMAD4-null mice exhibit early embryonic lethality (E6.5) due to mesoderm induction and extraembryonic defects.
  • The specific roles of SMAD4 in distinct embryonic germ layers are not fully understood.

Purpose of the Study:

  • To elucidate the functions of SMAD4 in the visceral endoderm and epiblast during early mouse embryogenesis.
  • To investigate the impact of SMAD4 disruption on mesoderm induction, anterior-posterior patterning, and gastrulation.

Main Methods:

  • Utilized a Cre-loxP system to specifically disrupt SMAD4 in the visceral endoderm (Smad4(Co/Co);TTR-Cre) and epiblast.
  • Analyzed embryonic development, gene expression (Hex1, Cer1, Lim1), and response to TGF-β in SMAD4-deficient embryos and embryoid bodies.

Main Results:

  • SMAD4 deficiency in the visceral endoderm (Smad4(Co/Co);TTR-Cre) led to embryonic lethality (E7.5-E9.5) with absent anterior structures and reduced expression of key anterior visceral endoderm (AVE) genes.
  • SMAD4-deficient embryoid bodies showed impaired TGF-β signaling responses.
  • Epiblast-specific SMAD4 disruption resulted in normal mesoderm and head-fold induction but caused significant later gastrulation patterning defects.

Conclusions:

  • SMAD4 signaling in the visceral endoderm is essential for anterior embryonic patterning and head induction via regulation of AVE genes.
  • SMAD4 signaling in the epiblast is dispensable for initial mesoderm induction but critical for later gastrulation patterning and head development.
  • These findings highlight distinct roles for SMAD4 in different germ layers during early embryogenesis.
Keywords:
AVESMAD4TGF-betaepiblastmesoderm patterning

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