Evaluation of Signaling Molecules in the Post-Autotomy Initiation Phase of Tail Regeneration in the Lizard Hemidactylus flaviviridis

Epimorphic regeneration, as exemplified by lizard tail, involves the formation of regeneration blastema as a pre-requisite for replacement growth. The formation of blastema is preceded by many regressive changes like tissue demolition, histolysis, inflammation, wound closure, de-differentiation, cell migration and proliferation. Induction of signaling molecules would be crucial in the molecular biology of immediate post-autotomy period in providing the trigger for the initiation of regeneration. It is in this behest that the levels of the cAMP, cGMP and NO have been assayed during the first 72 hr post caudal-autotomy in the lizard Hemidactylus flaviviridis. The influence of exaggerated exogenous induction of NO as well as prolonged action of cGMP by the use of PDE5 inhibitor (sidenafil citrate) have also been evaluated in terms of the number of days taken to complete wound healing and form a blastema as well as the length of tail regenerated at the end of 20 days. cAMP-mediated PKA activation and downstream signaling cascades appear to be the principal mechanism as against cGMP-mediated mechanisms. Controlled NO generation appears to be of pivotal significance in minimizing apoptotic cell loss as substantiated by the reduced caspase 3 activity. Exaggerated induction of NO and prolongation of cGMP action appear to promote apoptotic cell loss resulting in retarded regenerative growth. It can be concluded from the present observations that cAMP- and PKA-mediated events occur first and that minimizing cell apoptosis by controlled NO generation is important in the formation of robust regeneration blastema.