Practice question

Sonic hedgehog secreted from Hensen's node and left paraxial mesoderm plays pivotal role in left-right asymmetry, not just dorsoventral neural patterning. Shh induces Caronte, a Cerberus family BMP antagonist, on left side near node. Caronte inhibits BMP signaling locally, relieving BMP-mediated repression of Nodal in left lateral plate mesoderm via FoxH1 transcription. Right side FGF8 maintains BMP activity blocking Nodal. This Shh-Caronte-Nodal-Pitx2 cascade drives heart looping and gut coiling. Loss of asymmetric Shh randomizes situs, demonstrating crucial role in left-right asymmetry specification beyond neural tube closure.