Evolutionarily conserved function of Gbx2 in anterior hindbrain development.

The amino acid sequence across the DNA-binding homeodomain of Gbx2 is highly conserved across multiple species. In mice, Gbx2 is essential for establishment of the midbrain-hindbrain boundary (MHB), and in development of anterior hindbrain structures, rhombomeres (r) 1-r3, and the r2/r3-derived cranial nerve V. In contrast, studies in zebrafish have implicated gbx1 in establishment of the MHB. Therefore, we tested potential roles for gbx2 in anterior hindbrain development in zebrafish. gbx2 knockdown with antisense morpholino results in increased cell death in r2, r3, and r5 and a truncation of the anterior hindbrain, similar to the defect in Gbx2(-/-) mice. Moreover, there is abnormal clustering of cranial nerve V cell bodies in r2 and r3 indicative of defects in aspects of anterior hindbrain patterning. These phenotypes can be rescued by expression of the mouse GBX2 protein. These results suggest that gbx2/Gbx2 has an evolutionarily conserved role in anterior hindbrain development.