Mouse patched1 controls body size determination and limb patterning

Area of Science:

• Developmental biology
• Molecular genetics
• Genetics

Background:

• Hedgehog (Hh) proteins are crucial for embryonic development, regulating cell fate and proliferation.
• Patched1 (Ptc1) is an Hh-binding protein that antagonizes Hh signaling by repressing target gene transcription.
• Sonic hedgehog (Shh) plays a key role in vertebrate limb patterning and growth, but the function of Ptc1 in later development is unclear due to early embryonic lethality in ptc1(-/-) mice.

Purpose of the Study:

• To investigate the role of Patched1 (Ptc1) in later stages of embryonic development, particularly in limb development.
• To understand the mechanism by which Ptc1 regulates Sonic hedgehog (Shh) expression in the limb bud.

Main Methods:

• Generation of partially rescued ptc1 homozygous mutant mouse embryos using a metallothionein promoter driving Ptc1 expression.
• Analysis of embryonic morphology, focusing on limb development and anterior digit formation.
• Assessment of Shh expression patterns in the limb bud of wild-type and mutant embryos.

Main Results:

• Transgenic Ptc1 expression in a wild-type background resulted in reduced animal size and loss of anterior digits.
• Partially rescued ptc1 homozygotes survived to E14 with some morphological defects, including midbrain overgrowth.
• Partially rescued embryos exhibited exencephaly, polydactyly, and branched digits, preceded by anterior limb bud Shh transcription.

Conclusions:

• Patched1 (Ptc1) functions to repress Sonic hedgehog (Shh) expression in the anterior limb bud.
• Dysregulation of Ptc1 leads to developmental abnormalities in limb patterning and digit formation.
• Ptc1 is essential for controlling Shh expression and ensuring proper limb development.