Meeting Abstract

S2-2.2  Thursday, Jan. 3  Is Segmental Organization Presaged In or Imposed Upon Craniofacial Mesenchymal Populations? NODEN, Drew M.; Cornell University dmn2@cornell.edu

Many of the debates concerning segmental organization of the vertebrate head have centered upon issues of if, how, and when craniofacial mesenchymal populations such as cephalic paraxial mesoderm and the neural crest exhibit metameric organization. Throughout much of the head, these two populations share an expansive and dynamic interface, one that acts as a deterrent to movement for some cells and is readily penetrated by others. This interface provides the possibility that morphogenetic patterning in either population might result from influences emanating from or conveyed by the other. But is there evidence that such influences either depend upon or instill a segmental organization? Data from cell lineage analyses in several species combined with increasing information of patterns of gene expression within these mesenchymal populations warrant a re-examination of the classical models of head organization. Focusing on the mesoderm-crest interface, this presentation will highlight the locations and nature of cell:cell relations between these two populations, comparing the behaviors of several lineages and exploring the interactions that promote both the differentiation of these lineages and the morphogenesis of tissues that they form. Both phylogenetic and ontogenetic changes in the location of these interfaces, in the timing of interactions among or between them, and in the qualitative character of signals passing between will be discussed, with the goal of better understanding the diversity of outcomes evident in vertebrate craniofacial morphology. Data from avian cell lineage analyses using quail-chick transplantations and plasmid/retroviral infections to follow crest and mesodermal lineages will be integrated with the results of murine transgenic studies using tissue-specific reporter genes, and the utility of these data in clarifying underlying organizational strategies, e.g., segmentation, discussed.