Components of the reelin signaling pathway are expressed in the spinal cord

The Reelin signaling pathway in the brain involves the binding of Reelin to very-low-density lipoprotein receptors (VLDLR) and apolipoprotein E receptor 2 (ApoER2). After Reelin binds the lipoprotein receptors on migrating neurons, the intracellular adaptor protein Disabled-1 (Dab1) becomes phosphorylated, ultimately resulting in the proper positioning of cortical neurons. Previous work showed that Reelin also affects the positioning of sympathetic preganglionic neurons (SPN) in the spinal cord (Yip et al. [2000] Proc Natl Acad Sci USA 97:8612-8616). We asked in the present study whether components of the Reelin signaling pathway in the brain also function to control SPN migration in developing spinal cord. Results showed that Reelin and reelin mRNA are found adjacent to migrating SPN. In addition, dab1 mRNA and protein are expressed by migrating SPN, and dab1-null mice show abnormal SPN migration similar to that seen in reeler. Finally, vldlr and apoER2 are also expressed in migrating SPN, and mice lacking both vldlr and apoER2 show aberrant SPN location that is identical to that of reeler and dab1-null mice. Because molecules known to be involved in Reelin signaling in the brain are present in the developing spinal cord, it is likely that the Reelin signaling pathways in the brain and spinal cord function similarly. The relative simplicity of the organization of the spinal cord makes it a potentially useful model system with which to study the molecular and cellular function of the Reelin signaling pathway in control of neuronal migration.