Molecular control of spinal accessory motor neuron/axon development in the mouse spinal cord.
Within the developing vertebrate spinal cord, motor neuron subtypes are distinguished by the settling positions of their cell bodies, patterns of gene expression, and the paths their axons follow to exit the CNS. The inclusive set of cues required to guide a given motor axon subtype from cell body to target has yet to be identified, in any species. This is attributable, in part, to the unavailability of markers that demarcate the complete trajectory followed by a specific class of spinal motor axons. Most spinal motor neurons extend axons out of the CNS through ventral exit points. In contrast, spinal accessory motor neurons (SACMNs) project dorsally directed axons through lateral exit points (LEPs), and these axons assemble into the spinal accessory nerve (SAN). Here we show that an antibody against BEN/ALCAM/SC1/DM-GRASP/MuSC selectively labels mouse SACMNs and can be used to trace the pathfinding of SACMN axons. We use this marker, together with a battery of transcription factor-deficient or guidance cue/receptor-deficient mice to identify molecules required for distinct stages of SACMN development. Specifically, we find that Gli2 is required for the initial extension of axons from SACMN cell bodies, and that netrin-1 and its receptor Dcc are required for the proper dorsal migration of these cells and the dorsally directed extension of SACMN axons toward the LEPs. Furthermore, in the absence of the transcription factor Nkx2.9, SACMN axons fail to exit the CNS. Together, these findings suggest molecular mechanisms that are likely to regulate key steps in SACMN development.
Dillon
Allison K
AK
Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Fujita
Shinobu C
SC
Matise
Michael P
MP
Jarjour
Andrew A
AA
Kennedy
Timothy E
TE
Kollmus
Heike
H
Arnold
Hans-Henning
HH
Weiner
Joshua A
JA
Sanes
Joshua R
JR
Kaprielian
Zaven
Z
D000055:Accessory Nerve / Q000166:cytology / Q000196:embryology* / Q000378:metabolism*; D000818:Animals; D001369:Axons / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology; D005260:Female; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009046:Motor Neurons / Q000166:cytology / Q000378:metabolism*; D009124:Muscle Proteins / Q000096:biosynthesis; D009687:Nuclear Proteins / Q000096:biosynthesis; D011247:Pregnancy; D013116:Spinal Cord / Q000196:embryology / Q000378:metabolism; D015534:Trans-Activators / Q000096:biosynthesis
C486558:Gtf2ird1 protein, mouse; D009124:Muscle Proteins; D009687:Nuclear Proteins; D015534:Trans-Activators