The effect of sonic hedgehog on motor neuron positioning in the spinal cord during chicken embryo development

Abstract

Sonic hedgehog (Shh) is a vertebrate homologue of the secreted Drosophila protein 1 9 hedgehog, and is expressed by the notochord and the floor plate in the developing 2 0 spinal cord. Shh provides signals relevant for positional information, cell proliferation, 2 1 and possibly cell survival depending on the time and location of the expression. 2 2Although the role of Shh in providing positional information in the neural tube has 2 3 been experimentally proven, the exact underlying mechanism still remains unclear. In 2 4this study, we report that overexpression of Shh affects motor neuron positioning in 2 5 the spinal cord during chicken embryo development by inducing abnormalities in the 2 6 structure of the motor column and motor neuron integration. In addition, Shh 2 7 overexpression inhibits the expression of dorsal transcription factors and commissural 2 8 axon projections. Our results indicate that correct location of Shh expression is the 2 9 key to the formation of the motor column. In conclusion, the overexpression of Shh in 3 0 the spinal cord not only affects the positioning of motor neurons, but also induces 3 1 abnormalities in the structure of the motor column.