Rab23 GTPase is expressed asymmetrically in Hensen's node and plays a role in the dorsoventral patterning of the chick neural tube.

The mouse Rab23 protein, a Ras-like GTPase, inhibits signaling through the Sonic hedgehog pathway and thus exerts a role in the dorsoventral patterning of the spinal cord. Rab23 mouse mutant embryos lack dorsal spinal cord cell types. We cloned the chicken Rab23 gene and studied its expression in the developing nervous system. Chick Rab23 mRNA is initially expressed in the entire neural tube but retracts to the dorsal alar plate. Unlike in mouse, we find Rab23 in chick already expressed asymmetrically during gastrulation. Ectopic expression of Rab23 in ventral midbrain induced dorsal genes (Pax3, Pax7) ectopically and reduced ventral genes (Nkx2.2 and Nkx6) without influencing cell proliferation or neurogenesis. Thus, in the developing brain of chick embryos Rab23 acts in the same manner as described for the caudal spinal cord in mouse. These data indicate that Rab23 plays an important role in patterning the dorso-ventral axis by dorsalizing the neural tube.