The isthmic organiser, located at the boundary between the midbrain and hindbrain, secretes a morphogen that patterns the cerebellum and induces Engrailed gene expression in adjacent neuroepithelium. Which molecule does it secrete?

• A Retinoic acid
• B Endothelin 1
• C Noggin
• D FGF8 ✓

Explanation

The isthmic organiser at the midbrain-hindbrain boundary secretes FGF8, which maintains Engrailed expression and coordinates development of the midbrain tectum and the cerebellum. Ectopic FGF8 beads induce duplicate midbrain-cerebellar structures. Retinoic acid patterns the hindbrain rhombomeres posteriorly, Noggin is a BMP antagonist acting in neural induction, and endothelin 1 functions in pharyngeal arch and cardiovascular patterning.

Reference: Larsen's Human Embryology, 5th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.