Multiple inductive signals are involved in the development of the ctenophore Mnemiopsis leidyi

Ctenophores possess eight longitudinally arrayed rows of comb plate cilia. Previous intracellular cell lineage analysis has shown that these comb rows are derived from two embryonic lineages, both daughters of the four e(1) m icromeres (e(11), and e(12)) and a single daughter of the four m(1) microme res (the m(12) micromeres). Although isolated e(1) micromeres will spontane ously generate comb plates, cell deletion experiments have shown that no co mb plates appear during embryogenesis following the removal of e(1) descend ents. Thus, the m(1) lineage requires the inductive interaction of the e(1) lineage to contribute to comb plate formation. Here we show that, although m(12) cells are normally the only m(1) derivatives to contribute to comb p late formation, m(12) cells are capable of generating comb plates in the ab sence m(12) cells. The reason that m(11) cells do not normally make comb ro ws may be attributable either to their more remote location relative to cri tical signaling centers (e.g., e(1) descendants) or to inhibitory signals t hat may be provided by other nearby cells such as sister cells m(12). In ad dition, we show that the signals provided by the e(1) lineage are not suffi cient for m(1)-derived comb plate formation. Signals provided by endomesode rmal progeny of either the E or the M lineages (the 3E or 2M macromeres) ar e also required. (C) 2001 Academic Press.