The Relationship Between Embryonic and Adult Pattern Regulation

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9315653 Martindale Ctenophores are the first extant phylum of metazoan organisms whose body plan displays bilateral symmetry and evolved prior to the divergence of the protostomes and deuterostomes. Abundant evidence now exists which indicates that the major pattern forming mechanisms were in place prior to the protostome-deuterostome radiation. Ctenophores undergo a highly stereotyped mode of development in which the normal fate of individual blastomeres can be precisely predicted. Adult structures derived from deleted blasotmeres are not replaced by surviving blastomeres during subsequent embryogenesis. Adult ctenophores on the other hand are capable of regenerating vast regions of their body, including all pattern elements and cell types. Dr. Martindale's prior work has shown that ctenophore embryos are not mosaics of individual parts but that they have "organizing centers" analogous in their function to the dorsal lip in vertebrate embryos and the D quadrant in spiralian embryos. The deletion of this organizing center in ctenophore embryos results in abnormal development of several different structures to which these deleted cells themselves make no direct contribution. This implies that, as in adult regeneration, the embryo requires intercellular signaling. The experiments proposed here will advance our understanding of the mechanistic basis of this pattern regulation both in the ctenophore embryo and adult. The specific aims are: 1) To generate an accurate fate map of the ctenophore embryo to identify the origins of all known cell types, with special reference to the origins of nerve cells, mesenchymal cells, muscle cells, components of tentacle sheathes, and the pluripotent stem cells involved in adult regenerative ability, 2) to identify the spatial and temporal characteristics of inductive interactions which operate to establish global symmetry properties and cell type determination in the ctenophore embryo, 3) To finish a systematic study of the r ole of individual cell types on the ability of ctenophores to regenerate, and 4) To determine the role of cell division in the ability to regenerate adult pattern elements. Additionally, tools will be developed for the study of homeodomain transcription factor genes expressed in ctenophore embryos. ***