The neurotrophic effects of glial cell line-derived neurotrophic factor on spinal motoneurons are restricted to fusimotor subtypes.
Glial cell line-derived neurotrophic factor (GDNF) regulates multiple aspects of spinal motoneuron (MN) development, including gene expression, target selection, survival, and synapse elimination, and mice lacking either GDNF or its receptors GDNF family receptor alpha1 (GFRalpha1) and Ret exhibit a 25% reduction of lumbar MNs at postnatal day 0 (P0). Whether this loss reflects a generic trophic role for GDNF and thus a reduction of all MN subpopulations, or a more restricted role affecting only specific MN subpopulations, such as those innervating individual muscles, remains unclear. We therefore examined MN number and innervation in mice in which Ret, GFRalpha1, or GDNF was deleted and replaced by reporter alleles. Whereas nearly all hindlimb muscles exhibited normal gross innervation, intrafusal muscle spindles displayed a significant loss of innervation in most but not all muscles at P0. Furthermore, we observed a dramatic and restricted loss of small myelinated axons in the lumbar ventral roots of adult mice in which the function of either Ret or GFRalpha1 was inactivated in MNs early in development. Finally, we demonstrated that the period during which spindle-innervating MNs require GDNF for survival is restricted to early neonatal development, because mice in which the function of Ret or GFRalpha1 was inactivated after P5 failed to exhibit denervation of muscle spindles or MN loss. Therefore, although GDNF influences several aspects of MN development, the survival-promoting effects of GDNF during programmed cell death are mostly confined to spindle-innervating MNs.
Gould
Thomas W
TW
Laboratory for Neuronal Differentiation and Regeneration, RIKEN Center for Developmental Biology, Kobe 650-0047, Japan. tom.gould@oceaniamed.org
Yonemura
Shigenobu
S
Oppenheim
Ronald W
RW
Ohmori
Shiho
S
Enomoto
Hideki
H
D000818:Animals; D000831:Animals, Newborn; D053148:Caspase 3 / Q000378:metabolism; D004622:Embryo, Mammalian; D018507:Gene Expression Regulation, Developmental / Q000235:genetics; D051100:Glial Cell Line-Derived Neurotrophic Factor / Q000172:deficiency / Q000502:physiology*; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors / Q000172:deficiency; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006614:Hindlimb / Q000196:embryology / Q000254:growth & development / Q000294:innervation; D051379:Mice; D018345:Mice, Knockout; D009046:Motor Neurons / Q000145:classification* / Q000502:physiology*; D009470:Muscle Spindles / Q000196:embryology / Q000254:growth & development / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism; D017354:Point Mutation; D051096:Proto-Oncogene Proteins c-ret / Q000172:deficiency / Q000235:genetics; D013116:Spinal Cord / Q000166:cytology*; D050494:Vesicular Acetylcholine Transport Proteins / Q000235:genetics / Q000378:metabolism
D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; C493460:Slc18a3 protein, mouse; D050494:Vesicular Acetylcholine Transport Proteins; D049452:Green Fluorescent Proteins; D051096:Proto-Oncogene Proteins c-ret; C494999:Ret protein, mouse; D053148:Caspase 3