Molecular guidance cues necessary for axon pathfinding from the ventral cochlear nucleus.
During development, multiple guidance cues direct the formation of appropriate synaptic connections. Factors that guide developing axons are known for various pathways throughout the mammalian brain; however, signals necessary to establish auditory connections are largely unknown. In the auditory brainstem the neurons whose axons traverse the midline in the ventral acoustic stria (VAS) are primarily located in the ventral cochlear nucleus (VCN) and project bilaterally to the superior olivary complex (SOC). The circumferential trajectory taken by developing VCN axons is similar to that of growing axons of spinal commissural neurons. Therefore, we reasoned that netrin-DCC and slit-robo signaling systems function in the guidance of VCN axons. VCN neurons express the transcription factor, mafB, as early as embryonic day (E) 13.5, thereby identifying the embryonic VCN for these studies. VCN axons extend toward the midline as early as E13, with many axons crossing by E14.5. During this time, netrin-1 and slit-1 RNAs are expressed at the brainstem midline. Additionally, neurons within the VCN express RNA for DCC, robo-1, and robo-2, and axons in the VAS are immunoreactive for DCC. VCN axons do not reach the midline of the brainstem in mice mutant for either the netrin-1 or DCC gene. VCN axons extend in pups lacking netrin-1, but most DCC-mutant samples lack VCN axonal outgrowth. Stereological cell estimates indicate only a modest reduction of VCN neurons in DCC-mutant mice. Taken together, these data show that a functional netrin-DCC signaling system is required for establishing proper VCN axonal projections in the auditory brainstem.
Howell
David M
DM
Sensory Neuroscience Research Center, West Virginia University, Morgantown, West Virginia 26506, USA.
Morgan
Warren J
WJ
Jarjour
Andrew A
AA
Spirou
George A
GA
Berrebi
Albert S
AS
Kennedy
Timothy E
TE
Mathers
Peter H
PH
D000596:Amino Acids; D000818:Animals; D001306:Auditory Pathways / Q000196:embryology / Q000502:physiology*; D001369:Axons / Q000502:physiology*; D017626:Cochlear Nucleus / Q000166:cytology* / Q000196:embryology; D000075389:DCC Receptor; D004622:Embryo, Mammalian; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000235:genetics; D007150:Immunohistochemistry / Q000379:methods; D017403:In Situ Hybridization / Q000379:methods; D051379:Mice; D018345:Mice, Knockout; D009414:Nerve Growth Factors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D000075388:Netrin-1; D009474:Neurons / Q000166:cytology* / Q000502:physiology; D011247:Pregnancy; D011956:Receptors, Cell Surface / Q000172:deficiency; D011971:Receptors, Immunologic / Q000235:genetics / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D000097905:Roundabout Proteins
D000596:Amino Acids; D000075389:DCC Receptor; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins; D000075388:Netrin-1; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D025521:Tumor Suppressor Proteins; D000097905:Roundabout Proteins; C501910:Dcc protein, mouse; C000617353:Ntn1 protein, mouse; C498888:Robo2 protein, mouse; C120010:Slit1 protein, mouse; C098463:dolaisoleucine