Neural regulation of body polarities in nereid worm regeneration.

Nerve dependence in regeneration has been established more than 200 years ago but the mechanisms by which nerves are necessary to regeneration remain to be fully elucidated. Aside from their direct impact in stimulating cellular growth, nerves also have a role on the establishment of body polarities (antero-posterior and dorso-ventral patterns) and this has been particularly well studied in nereid annelid worms. Nereids can regenerate appendages (parapodia) and the tail (body segments). In both parapodia and tail regeneration, the presence of the nerve cord is necessary to the establishment of body polarities. In this review, we will detail the experimental procedures which have been conducted in nereids to elucidate the role of the nerve cord in the establishment of the antero-posterior and dorso-ventral polarities. Most of the studies reported here were published several decades ago and based on anatomical and histological analyses; this review should constitute a knowledgebase and an inspiration for needed modern-time explorations at the molecular levels to elucidate the impact of the nervous system in the acquisition of body polarities.