Lrrn1 is required for formation of the midbrain-hindbrain boundary and organiser through regulation of affinity differences between midbrain and hindbrain cells in chick

►Lrrn1 is expressed in midbrain cells but not in anterior hindbrain cells. ►Lrrn1 is down-regulated in anterior hindbrain by FGF8. ►Lrrn1 creates a differential affinity between midbrain and hindbrain compartments. ►This forms a sharp compartment boundary at the midbrain-hindbrain interface. ►Lrrn1 is required for formation of the mid-hindbrain boundary.