Differential expression of the GDNF family receptors RET and GFRα1, 2, and 4 in subsets of motoneurons: A relationship between motoneuron birthdate and receptor expression

Abstract

Previous studies have demonstrated the expression of specific members of the glial cell line-derived neurotrophic factor (GDNF) receptor family α (GFRα) in subsets of motoneurons (MNs) in the developing mouse spinal cord. We examined the expression pattern of GFRα and RET in the avian lumbar spinal cord during the period of programmed cell death (PCD) of MNs by using double labeling in situ hybridization and immunohistochemistry. In the lateral motor column (LMC) of the lumbar spinal cord, a laminar organization of GFRα expression was observed: GFRα1-positive MNs were located in the medial LMC; GFRα1-, 2-, and 4-positive MNs were situated in the lateral LMC; and GFRα4-positive MNs were located in the intermediate LMC. The species of GFRα receptor that was expressed in MNs was found to be related to their birthdates. The expression of subpopulation-specific transcriptional factors was also used to define MNs that express a specific pattern of GFRα. This analysis suggests that motor pools as defined by these transcriptional factors have unique expression patterns of GFRα receptor. Early limb bud ablation did not affect the expression of GFRα in the spinal cord, indicating that regulation of receptor expression is independent of target-derived signals. Finally, GDNF mRNA expression was found in the limb during the PCD period of MNs. In conclusion, these results indicate that time of withdrawal from the mitotic cycle may specify the expression pattern of GFRα in subsets of MNs and that GDNF may function as a target-derived neurotrophic factor for specific subpopulations of MNs. J. Comp. Neurol. 456:245–259, 2003.