Regeneration neurohormones and growth factors in echinoderms

There has been much recent interest in the presence and biological function s of growth regulators in invertebrates. In spite of the different distribu tion patterns of these molecules in different phyla (from molluscs, insects , and annelids to echinoderms and tunicates), they seem always to be extens ively involved in developmental processes, both embryonic and regenerative. Echinoderms are well known for their striking regenerative potential and m any can completely regenerate arms that, for example, are lost following se lf-induced or traumatic amputation. Thus, they provide a valuable experimen tal model for the study of regenerative processes from the macroscopic to t he molecular level. In crinoids as well as probably all ophiuroids, regener ation is rapid and occurs by means of a mechanism that involves blastema fo rmation, known as epimorphosis, where the new tissues arise from undifferen tiated cells. In asteroids, morphallaxis is the mechanism employed, replace ment cells being derived from existing tissues following differentiation an d (or) transdifferentiation. This paper focuses on the possible contributio n of neurohormones and growth factors during both repair and regenerative p rocesses. Three different classes of regulatory molecules are proposed as p lausible candidates for growth-promoting factors in regeneration: neurotran smitters (monoamines), neuropeptides (substance P, SALMFamides 1 and 2), an d growth-factor-like molecules (TGF-beta (transforming growth factor beta), NGF (nerve growth factor), RGF-2 (basic fibroblast growth factor)).