Mutations in a Human <i>ROBO</i> Gene Disrupt Hindbrain Axon Pathway Crossing and Morphogenesis

TLDR

Axon guidance mechanisms, especially the midline crossing of corticospinal and somatosensory axons in the hindbrain, are essential for establishing contralateral motor and sensory pathways. The study identified mutations in the ROBO3 gene in HGPPS patients, linking this gene—homologous to roundabout axon‑guidance genes in model organisms—to hindbrain axon midline crossing. Patients with HGPPS show uncrossed motor and sensory projections, indicating disrupted hindbrain axon midline crossing.

Abstract

The mechanisms controlling axon guidance are of fundamental importance in understanding brain development. Growing corticospinal and somatosensory axons cross the midline in the medulla to reach their targets and thus form the basis of contralateral motor control and sensory input. The motor and sensory projections appeared uncrossed in patients with horizontal gaze palsy with progressive scoliosis (HGPPS). In patients affected with HGPPS, we identified mutations in the ROBO3 gene, which shares homology with roundabout genes important in axon guidance in developing Drosophila, zebrafish, and mouse. Like its murine homolog Rig1/Robo3, but unlike other Robo proteins, ROBO3 is required for hindbrain axon midline crossing.