Receptor Allostery Promotes Context-Dependent Sonic Hedgehog Signaling During Embryonic Development

Area of Science:

• Developmental Biology
• Molecular Biology
• Biochemistry

Background:

• Sonic Hedgehog (SHH) signaling is essential for embryonic development, patterning diverse tissues.
• The signal transducer Smoothened (SMO) is activated by ligands including sterols, oxysterols, and arachidonic acid (AA).
• Allosteric regulation of SMO by combinatorial ligand binding is suggested by in vitro studies, but in vivo evidence is lacking.

Purpose of the Study:

• To investigate the in vivo role of arachidonic acid (AA) binding in Smoothened (SMO) allosteric regulation.
• To elucidate the functional consequences of disrupted AA binding to SMO during embryogenesis.
• To determine the impact of compromised SMO-AA interaction on SHH pathway activity and tissue development.

Main Methods:

• Mapping of an AA binding pocket within the 7-transmembrane (7TM) bundle of SMO.
• Generation and analysis of a knockin mouse model with compromised AA binding to SMO.
• Assessment of SHH pathway induction and developmental phenotypes in mutant mice.

Main Results:

• Disruption of the AA binding pocket attenuates SHH and sterol-stimulated SMO induction.
• Homozygous mutant mice exhibit cyanosis, high perinatal lethality, and congenital heart disease.
• Surviving mutants display pulmonary maldevelopment and failure to thrive, while neurodevelopment remains unaffected.

Conclusions:

• Arachidonic acid (AA) binding to SMO is critical for SHH pathway activation in vivo.
• Context-dependent allosteric regulation of SMO by AA is essential for proper cardiopulmonary development.
• Compromised SMO-AA interaction leads to severe developmental defects, highlighting the pathway's role in heart and lung formation.