Gene expression profiling reveals that peripheral nerve regeneration is a consequence of both novel injury-dependent and reactivated developmental processes.

One of the most striking features of the injured mature peripheral nervous system is the ability to regenerate. The lesioned peripheral nervous system displays stereotypic histopathological reactions indicating the activation of a co-ordinated lesion-induced gene expression programme. Previous research has already identified molecular components of this axonal switch from a mature transmitting to a regenerative growth mode. The observed alterations in gene expression within the lesioned distal nerve stump were largely attributed to recapitulated developmental processes. However, to our knowledge, this hypothesis has not been proven systematically. Most of the stereotypic molecular and cellular reactions during nerve development and repair can be assigned to specific time windows. Consequently, we have compared gene expression profiles of both paradigms at six different time-points each by means of cDNA array hybridization. Our data identified injury-specific molecular reactions and revealed to what extent developmental mechanisms are reactivated in response to nerve lesion. Ninety-one genes (47% of the regeneration-associated genes) were found to be significantly regulated in both paradigms, suggesting that regeneration only partially recapitulates development and that approximately half of the regulated genes are part of a regeneration-dependent programme. Interestingly, mainly genes encoding signal transducers or factors involved in processes such as cell death, immune response, transport and transcriptional regulation showed injury-specific gene expression.