The chick oligozeugodactyly (ozd) mutant lacks sonic hedgehog function in the limb

Area of Science:

• Developmental Biology
• Genetics
• Molecular Biology

Background:

• Limb development is a complex process regulated by signaling pathways.
• Sonic hedgehog (Shh) is a key signaling molecule in vertebrate limb patterning.

Purpose of the Study:

• To characterize a novel chicken limb mutant, oligozeugodactyly (ozd).
• To investigate the role of Shh signaling in chicken limb development.

Main Methods:

• Analysis of a spontaneous chicken limb mutant (ozd).
• Recombination experiments to identify the defective tissue layer.
• Molecular analysis of gene expression (Shh, Ptc1, Gli1, Bmp2, dHAND, Hoxd, Fgf).
• Limb bud grafting and protein/retinoic acid rescue experiments.

Main Results:

• The ozd mutant exhibits postaxial limb defects, lacking posterior zeugopod elements and most digits.
• Limb mesoderm is identified as the defective tissue in ozd mutants.
• Absence of Shh expression in ozd limb buds, with normal Shh expression in other organs.
• Downregulation of Ptc1, Gli1, and altered Hoxd and Fgf expression.
• Shh protein or ZPA grafts restore normal limb patterning, while retinoic acid does not induce Shh.

Conclusions:

• Shh signaling is essential for chicken limb development distal to the elbow/knee joints.
• The ulna, fibula, and all but digit 1 of the leg are Shh-dependent.
• The ozd mutation likely results from a defect in a limb-specific Shh regulatory element.