Integrity of developing spinal motor columns is regulated by neural crest derivatives at motor exit points.
Spinal motor neurons must extend their axons into the periphery through motor exit points (MEPs), but their cell bodies remain within spinal motor columns. It is not known how this partitioning is established in development. We show here that motor neuron somata are confined to the CNS by interactions with a neural crest subpopulation, boundary cap (BC) cells that prefigure the sites of spinal MEPs. Elimination of BC cells by surgical or targeted genetic ablation does not perturb motor axon outgrowth but results in motor neuron somata migrating out of the spinal cord by translocating along their axons. Heterologous neural crest grafts in crest-ablated embryos stop motor neuron emigration. Thus, before the formation of a mature transitional zone at the MEP, BC cells maintain a cell-tight boundary that allows motor axons to cross but blocks neuron migration.
Vermeren
Matthieu
M
MRC Centre for Developmental Neurobiology, Guy's Campus, King's College London, SE1 1UL, London, United Kingdom.
Maro
Géraldine S
GS
Bron
Romke
R
McGonnell
Imelda M
IM
Charnay
Patrick
P
Topilko
Piotr
P
Cohen
James
J
D000818:Animals; D001369:Axons / Q000502:physiology; D002465:Cell Movement / Q000502:physiology; D002642:Chick Embryo; D004268:DNA-Binding Proteins / Q000235:genetics; D003714:Denervation; D051379:Mice; D008817:Mice, Mutant Strains; D008866:Microsurgery; D009046:Motor Neurons / Q000502:physiology* / Q000648:ultrastructure; D009432:Neural Crest / Q000166:cytology* / Q000196:embryology* / Q000637:transplantation; D000072041:PAX3 Transcription Factor; D051761:Paired Box Transcription Factors; D011784:Quail; D013116:Spinal Cord / Q000166:cytology* / Q000196:embryology*; D013126:Spinal Nerve Roots / Q000166:cytology / Q000196:embryology; D014157:Transcription Factors
D004268:DNA-Binding Proteins; D000072041:PAX3 Transcription Factor; D051761:Paired Box Transcription Factors; D014157:Transcription Factors; C068686:Pax3 protein, mouse