Exciting break-through studies have shown that femto-second laser surgery can sever individual C. elegans neuronal processes in the living animal without damaging the surrounding tissue (Yanik MF et al., Nature 432:822; Gabel, C.V., Chuang, C., Samuel, A.D.T., Chang, C., Axon regeneration in adult neurons requires novel regulation of axon guidance molecules. Submitted, 2007). Interestingly, some severed neurons have the ability to regenerate. For example, when we used femto-second laser pulses to axotomize ALMs touch neurons visualized by p<sub>
mec-4</sub>::GFP, we observed ALM axon regeneration consequent to microsurgery. Axonal regeneration after injury requires the remodeling of cytoplasmic and membranous components, formation of a growth cone, and axon extension. The distal axon and some of the proximal axon generated by the surgery appear to degenerate. These initial observations have set the stage for dissection of regeneration genetics in physiological context in C. elegans. Cell death genes are well documented to orchestrate cellular demise. However, even key cell death executors such as conserved cysteine protease caspases can "behave well" to contribute to fundamental biological processes that are distinct from cell killing (Campbell DS et al., Neuron. 37(6):939). We wondered whether cell death genes contribute to neuronal regeneration, possibly by impacting the degenerative aspects of this process. To test for roles of cell death genes in regeneration, we have been severing ALM axons and observing their regeneration in genetic backgrounds altered for necrosis, apoptosis, and cell corpse elimination. We found that
ced-3(
n2452) exhibits significantly diminished regeneration capacity. Since
ced-3(
n2452) is a deletion that takes out multiple genes, we also tested
ced-3 allele
n2433, which encodes a single amino acid substitution that disrupts the caspase active site. We find that
ced-3(
n2433) is also impaired for regeneration, supporting that
ced-3 caspase activity is critical for efficient neuronal regrowth consequent to injury. Our work constitutes the first in vivo survey of how specific death genes alter the ability of individual neurons to reconnect. We will present details of regeneration time lapse data and results from our more extensive genetic survey of death genes at the meeting.