Cellular and molecular bases of arm regeneration in Brittlestars

We have studied arm regeneration in a range of brittlestars with a particular emphasis on the nervous system. Regeneration is common in this group of echinoderms and forms part of their normal life-pattern where body parts may be lost following predator or hydrodynamic stress. Our approach has been to combine laboratory studies with an analysis of naturally regenerating animals from the field. Regeneration is a remarkably rapid process with as much as l-2mm of re-growth recorded in Amphiura filiformis over 10 days at 10-11°C. As in crinoids the process involves the formation of a blastema. This is produced by the active proliferation of cells, which accumulate at the end of the radial nerve cord. Following blastema formation the arms appear to extend from the tip with segmental maturity occurring in a temporally regulated fashion and proximal-distal (disk to tip) direction. An advantage of A. filiformis is its natural bioluminescence and this feature has allowed us to assess the extent of functional recovery in the regenerate. Initial results suggest that this system is capable of extensive and rather rapid reformation with function in the regenerated part restored just over one week following ablation. We are also investigating the role of growth factors in this process as well as the expression of patterning genes and are currently analysing cDNA libraries prepared from both regenerating and normally growing arms.