Extracellular matrix gene expression during arm regeneration in Amphiura filiformis.

Extracellular matrix (ECM) plays a dynamic role during tissue development and re-growth. Body part regeneration efficiency relies also on effective ECM remodelling and deposition. Among invertebrates, echinoderms are well known for their striking regenerative abilities since they can rapidly regenerate functioning complex structures. To gather insights on the involvement of ECM during arm regeneration, the brittle star Amphiura filiformis was chosen as experimental model. Eight ECM genes were identified and cloned, and their spatio-temporal and quantitative expression patterns were analysed by means of whole mount in situ hybridisation and quantitative PCR on early and advanced regenerative stages. Our results show that almost none of the selected ECM genes are expressed at early stages of regeneration, suggesting a delay in their activation that may be responsible for the high regeneration efficiency of these animals, as described for other echinoderms and in contrast to most vertebrates. Moreover, at advanced stages, these genes are spatially and temporally differentially expressed, suggesting that the molecular regulation of ECM deposition/remodelling varies throughout the regenerative process. Phylogenetic analyses of the identified collagen-like genes reveal complex evolutionary dynamics with many rounds of duplications and losses and pinpointed their homologues in selected vertebrates. The study of other ECM genes will allow a better understanding of ECM contribution to brittle star arm regeneration.