Bid Expression Controls Neuronal Cell Fate During Avian Ciliary Ganglion Development. Gallus gallus

To elucidate molecular networks regulating important aspects of parasympathetic neuronal development, a genome-wide expression analysis was performed during multiple stages of avian ciliary ganglion (CG) development. The transcriptome data showed a well-defined sequence of events, starting from neuronal migration via neuronal fate cell determination, synaptic transmission, regulation of synaptic plasticity to growth factor associated signaling. Focusing on cell death-related changes in the transcriptome, we could characterize a series of events that starts with the activation of neuronal apoptotic processes at E7 via the cell death execution phase at E8 and E9 and ends with apoptotic cell clearance at E14. Moreover, we detected a transient up-regulation of the transcription factors TP53 and RARB that was linked to cell death. The expression of BID, a p53 target, was also found to be dynamically regulated. Using a virus-based RNAi knockdown approach, BID expression was shown to be crucial for the execution of ontogenetic programmed cell death (PCD). Therefore, this study for the first time provides a comprehensive analysis of CG neuron development on the transcriptome level, revealing a temporally well-controlled expression of genes regulating ontogenetic PCD, with BID being one of the most dynamically regulated genes during the cell death phase. The effect of BID silencing in vivo suggests an essential role of BID expression in neuronal development. Overall design: Ciliary ganglia were dissected from chicken embryos at E6,E7, E8, E9, E10 and E14. For each analyzed time point, ganglia from at least 40 embryos were pooled for RNA extraction using the Qiagen RNeasy micro kit (Qiagen, Hilden, Germany) according to manufacturer's instructions. Four replicate sample of each time point were obtained.