Kwon, H.B., Fukuhara, S., Asakawa, K., Ando, K., Kashiwada, T., Kawakami, K., Hibi, M., Kwon, Y.G., Kim, K.W., Alitalo, K., and Mochizuki, N. (2013) The parallel growth of motoneuron axons with the dorsal aorta depends on Vegfc/Vegfr3 signaling in zebrafish. Development (Cambridge, England). 140(19):4081-4090.
Blood vessels and neurons grow often side by side. However, the molecular and cellular mechanisms underlying their parallel
development remain unclear. Here, we report that a subpopulation of secondary motoneurons extends axons ventrally outside
of the neural tubes and rostrocaudally as a fascicle beneath the dorsal aorta (DA) in zebrafish. We tried to clarify the mechanism
by which these motoneuron axons grow beneath the DA and found that Vegfc in the DA and Vegfr3 in the motoneurons were essential
for the axon growth. Forced expression of either Vegfc in arteries or Vegfr3 in motoneurons resulted in enhanced axon growth
of motoneurons over the DA. Both vegfr3 morphants and vegfc morphants lost the alignment of motoneuron axons with DA. In addition, forced expression of two mutant forms of Vegfr3 in
motoneurons, potentially trapping endogenous Vegfc, resulted in failure of growth of motoneuron axons beneath the DA. Finally,
a vegfr3 mutant fish lacked the motoneuron axons beneath the DA. Collectively, Vegfc from the preformed DA guides the axon growth
of secondary motoneurons.