Meeting Abstract

P3.75  Friday, Jan. 6  MAPK activation and early development in the calyptraeid gastropods LESOWAY, M.P.*; COLLIN, R.; ABOUHEIF, E.; HENRY, J.J.; McGill University, Montreal and Smithsonian Tropical Research Institute (STRI), Panama; STRI, Panama; McGill University, Montreal; U. of Illinois, Urbana

The calyptraeid gastropods have undergone numerous transitions in mode of development with little apparent phylogenetic constraint. The developmental mechanisms underlying these transitions remain unknown, but in other groups such as echinoderms, similar transitions are associated with shifts in the timing of axis specification. Mitogen activated protein kinases (MAP kinases; or extracellular signal-related kinases, ERK) have been implicated in early signaling events in the D quadrant of spiralian lophotrochozoans, the lineage responsible for dorso-ventral axis patterning and mesoderm specification. Previous work with the indirectly developing calyptraeid gastropod, Crepidula fornicata, has shown that MAPK activation is consistent with the timing of D quadrant specification. Embryos of the direct developing calyptraeids C. convexa, (a direct developer with large eggs) and C. cf. onyx Panama (a direct developer with nurse embryos) were immunologically stained for activated MAPK. The pattern of MAPK activation was similar to that described for C. fornicata, with MAPK activated in the 3D cell at the 24-cell stage and the 4d cell at the 25-cell stage in both species. The direct developer with large eggs showed an earlier arrest in MAPK activation, perhaps due to slower cleavage times associated with increased egg size. Staining in the nurse embryo developer was uneven, and it remains unclear how organizer activity is related to formation of nurse embryos.