Regulation and regeneration in the ctenophore Mnemiopsis leidyi

Lobate ctenophores (tentaculates) generally exhibit a remarkable ability to regenerate missing structures as adults. On the other hand, their embryos exhibit a highly mosaic behavior when cut into halves or when specific cell s are ablated. These deficient embryos do not exhibit embryonic regulation, and generate incomplete adult body plans. Under certain conditions, howeve r, these deficient animals are subsequently able to replace the missing str uctures during the adult phase in a process referred to as "post-regenerati on." We have determined that successful post-regeneration can be predicted on the basis of a modified polar coordinate model, and the rules of interca lary regeneration, as defined by French et nl. (V. French, P. J. Bryant, an d S. V. Bryant, 1976, Science 193, 969-981.) The model makes certain assump tions about the organization of the ctenophore body plan that fit well with what we have determined on the basis of cell lineage fates maps, and their twofold rotational ("biradial") symmetry. The results suggest that cells c omposing the ctenophore adult body plan possess positional information, whi ch is utilized to reconstruct the adult body plan. More specifically, we ha ve found that the progeny of three specific cell lineages are required to s upport post-regeneration of the comb rows (the e(1), e(2), and m(1) microme res). Furthermore, post-regeneration of the comb rows involves a suite of c ell-cell inductive interactions, which are similar to those that take place during their embryonic formation. The significance of these findings is di scussed in terms of the organization of the ctenophore body plan, and the m echanisms involved in cell fate specification. This situation is also contr asted with that of the atentaculate ctenophores, which are unable to underg o post-regeneration. (C) 2000 Academic Press.