Conserved requirement for EGF-CFC genes in vertebrate left-right axis formation

Area of Science:

• Developmental Biology
• Genetics
• Molecular Biology

Background:

• Left-right (L-R) axis specification in vertebrate embryos depends on positional information transfer from the node to the lateral plate mesoderm, leading to asymmetric gene expression.
• The Epidermal Growth Factor-Cysteine-Rich Factor (EGF-CFC) family of extracellular factors are known to play roles in embryonic development.

Purpose of the Study:

• To investigate the role of the EGF-CFC family, specifically murine Cryptic and zebrafish one-eyed pinhead (oep), in establishing L-R axis asymmetry.
• To determine if EGF-CFC activity is required for the transfer of L-R positional information from the node to the lateral plate mesoderm.

Main Methods:

• Targeted disruption of the Cryptic gene in mice.
• Partial rescue of zebrafish oep mutants via mRNA injection.
• Analysis of L-R asymmetric gene expression patterns (Nodal, Lefty, Pitx2) in mutant embryos.

Main Results:

• Cryptic disruption in mice led to L-R laterality defects, including randomized situs, hyposplenia, pulmonary right isomerism, and abnormal embryo turning/cardiac looping.
• Zebrafish oep mutants exhibited heterotaxia, such as randomized heart looping and pancreas location.
• In both Cryptic and oep mutants, L-R asymmetric expression of Nodal, Lefty2/antivin, and Pitx2 was absent in the lateral plate mesoderm.
• Asymmetric Nodal expression at the node remained in Cryptic mutants, indicating L-R specification occurred in the node but not transferred effectively.

Conclusions:

• The evolutionarily conserved activity of EGF-CFC family members is essential for L-R lateral asymmetry.
• A signaling pathway involving Nodal and EGF-CFC activities is critical for transferring L-R positional information from the node to the lateral plate.
• Defects in this pathway result in significant L-R laterality defects in vertebrate embryos.