Abstract
Sonic hedgehog (SHH) is a vertebrate homologue of the secreted Drosophila protein hedgehog and is expressed by the notochord and floor plate in the developing spinal cord. Sonic hedgehog provides signals relevant for positional information, cell proliferation and possibly cell survival, depending on the time and location of expression. Although the role of SHH in providing positional information in the neural tube has been experimentally proven, the underlying mechanism remains unclear. In this study, in ovo electroporation was employed in the chicken spinal cord during chicken embryo development. Electroporation was conducted at stage 17 (E2.5), after electroporation the embryos were continued incubating to stage 28 (E6) for sampling, tissue fixation with 4% paraformaldehyde and frozen sectioning. Sonic hedgehog and related protein expressions were detected by in situ hybridization and fluorescence immunohistochemistry and the results were analysed after microphotography. Our results indicate that the ectopic expression of SHH leads to ventralization in the spinal cord during chicken embryonic development by inducing abnormalities in the structure of the motor column and motor neuron integration. In addition, ectopic SHH expression inhibits the expression of dorsal transcription factors and commissural axon projections. The correct location of SHH expression is vital to the formation of the motor column. Ectopic expression of SHH in the spinal cord not only affects the positioning of motor neurons, but also induces abnormalities in the structure of the motor column. It leads to ventralization in the spinal cord, resulting in the formation of more ventral neurons forming during neuronal formation.
Highlights
During central nervous system development, many factors can be controlled to ensure normal development
We focus on the role of Sonic hedgehog (Shh) in motor neuron positioning in the spinal cord during chicken embryo development by inducing its misexpression in the embryonic spinal cord
After 36, 60, and h following electroporation, GFP-positive embryos were collected at stage 24-26 (E4-E6), and the overexpression of Shh was clearly observed using in situ hybridization (Fig. 1A-C, arrows [→] indicate the areas of Shh overexpression)
Summary
During central nervous system development, many factors can be controlled to ensure normal development. The notochord and floor plate at the ventral midline of the neural tube determine, in part, the organization of the developing spinal cord (Pringle et al, 1996) These structures emit signals that can induce the development of distant motor neurons (Yamada et al, 1991, 1993; Tanabe et al., 1995). HB9 is expressed in all somatic MN, whereas Foxp, Lim, and Islet are all expressed in lateral motor column MN at high levels (Vermot et al, 2005; Bonanomi and Pfaff, 2010; Santiago et al, 2014; Luxey et al, 2015) All these transcription factors have been shown to contribute to the establishment of MN organization in the spinal cord
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