Initial axon growth rate from embryonic sensory neurons is correlated with birth date

Anthony R Horton,Alun M Davies

doi:10.1002/dneu.22743

Abstract

Axon growth rate from different populations of sensory neurons is correlated with the distance they have to grow to reach their targets in development: neurons with more distant targets extend axons at intrinsically faster rates. With growth of the embryo, later‐born neurons within each population have further to extend their axons to reach their targets than early‐born neurons. Here we examined whether the axon growth rate is related to birth date by studying the axon growth from neurons that differentiate in vitro from precursor cells isolated throughout the period of neurogenesis. We first showed that neurons that differentiated in vitro from different precursor cell populations exhibited differences in axon growth rate related to in vivo target distance. We then examined the axon growth rate from neurons that differentiate from the same precursor population at different stages throughout the period of neurogenesis. We studied the epibranchial placode precursors that give rise to nodose ganglion neurons in the chicken embryo. We observed a highly significant, threefold difference in axon growth rate from neurons that differentiate from precursor cells cultured early and late during the period of neurogenesis. Our findings suggest that intrinsic differences in axon growth rate are correlated with the neuronal birth date.

Highlights

In the developing vertebrate peripheral nervous system, newly differentiated neurons initially survive independently of neurotrophins when their axons are growing to their targets and become dependent on target-derived neurotrophins for survival when their axons reach their targets (Davies, 1987)
If dissociated cultures of different populations of sensory neurons are established when their axons are starting to grow to their targets in vivo, initial axon growth rate is correlated with target distance; the further axons have to grow, the faster they grow
To examine the possibility that initial axon growth rate is correlated with birth date, we focused on the neurons of the chicken embryo nodose ganglion

Summary

Introduction

In the developing vertebrate peripheral nervous system, newly differentiated neurons initially survive independently of neurotrophins when their axons are growing to their targets and become dependent on target-derived neurotrophins for survival when their axons reach their targets (Davies, 1987). If dissociated cultures of different populations of sensory neurons are established when their axons are starting to grow to their targets in vivo, initial axon growth rate is correlated with target distance; the further axons have to grow, the faster they grow.

Results

Conclusion