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their signal by binding to a fibroblast growth factor receptor (FGFR) which has an intracellular protein tyrosine kinase domain. The tyrosine kinase domain is activated upon FGF binding, resulting in the activation of a transcription factor by means of a signal transduction cascade (Gilbert2000). Specifically, it has been demonstrated that FGF10 signaling is required for limb bud initiation (Min et al. 1998). Also, it has been demonstrated that FGF8 is necessary to define the hindbrain and forebrain in early chick development (2000).
Another paracrine factor, Sonic hedgehog (SHH), is crucial to many developmental processes such as the dorsal-ventral specification of the neural tube, limb development, lung development, and craniofacial development. SHH functions by binding to a transmembrane receptor, Patched (Ptc). In the presence of SHH, Ptc initiates a signal transduction cascade bythat ultimately results in the transcriptional activity of a target gene (Gilbert 2000). Inhibiting SHH signaling using cyclopamine results in the cyclopia, the fusion of frontal facial processes.
Chicks were exposed to SU5402, a fibroblast growth factor inhibitor, to study the effects on development. During chick embryo development, sonic hedgehog and FGF signals work in a feedback loop which allows for development in various areas, especially the craniofacial region. Since FGF is a major chemical signal in development and closely associated with SHH, developmental defects were expected when exposed to the inhibitor. Chick eggs were injected after 2 days of incubation with a control solution, DMSO and Howard Ringer's Solution,

©Cebra-Thomas, 2001

Last Modified: 2 August 2001

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