Control of programmed cell death by Rho-like GTPases-activated signalling cascades in the developing neuron

Neuronal apoptosis is an essential process occurring not only during normal development but also in pathological situations including stroke, traumatic brain injury and neurodegenerative diseases. The mechanisms underlying neuronal cell death have begun to be unravelled. Rat superior cervical ganglion neurons (SCGs) have proven to be a good study model as they die by apoptosis when withdrawn from nerve growth factor (NGF). It has previously been shown that upregulation of the c-Jun transcription factor and of its phosphorylation are essential for NGF withdrawal-induced apoptosis in SCG neurons. This thesis tries to identify the signalling molecules that mediate apoptosis of SCG neurons via the c-Jun transcriptional pathway. The Rho-like GTPases Cdc42 and Rac1 have been shown to be involved in the activation of the c-Jun-NH2-terminal kinase (JNK) pathway in other systems and therefore an investigation into the role of these GTPases was carried out. Here, it is demonstrated that Cdc42 and Rac1, but not RhoA or Ras, are required for cell death of SCG neurons and that they activate the JNK pathway, thereby inducing neuronal apoptosis. A further examination of the signalling molecules that would lie between Cdc42 and JNK on the death signaling pathway was then conducted. Here it is shown that two mitogen activated protein kinase kinase kinases (MAPKKKs), ASK1 and MLK3, are crucial elements of NGF withdrawal- induced activation of the Cdc42-c-Jun pathway and neuronal apoptosis