Specification and Patterning of the Animal-Vegetal Axis

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0110532WikramanayakeDepletion of nuclear beta-catenin in early sea urchin embryos affects thefates of multiple cell lineages along the animal-vegetal (A/V) axis. It isknown that the micromeres, which form the early signaling center thatspecifies mesendoderm, require nuclear beta-catenin to become competent tocarry out their inductive functions. Beta-catenin signaling is alsorequired in the veg2 lineage for these cells to respond to micromeresignals and to become specified as mesendoderm. Identifyingtranscriptional targets of beta-catenin and elucidating their functionswould be a critical step in defining the molecular basis of mesendodermspecification. This proposal will focus on SUWnt8, a nuclearbeta-catenin-sensitive Wnt gene that is activated in the micromerescoincident with the entry of beta-catenin into the nuclei of these cellsand in the veg2 tier shortly after transit of beta-catenin into the nucleiof this cell tier. Four proposed specific aims will define the function ofSUWnt8 in these cell lineages and will further the understanding ofmesendoderm specification in the sea urchin embryo. These aims are: (1) Todetermine the role of cell interactions in regulating early SUWnt8expression in the mesendoderm domain. This will provide insight into therelative roles of cell autonomous and non cell-autonomous mechanisms inearly mesendoderm specification. (2) To determine how SUWnt8 participatesin early mesendoderm specification by elucidating its role in themicromeres and the veg2 tier by blocking its activity using morpholinoantisense oligonucleotide-mediated translational inhibition. Additionally,a possible role for SUWnt8 in maintaining nuclear beta-catenin levels invegetal cells and in suppressing the activity of animalizing transcriptionfactors in vegetal cells will be determined. (3) While nuclearbeta-catenin is required for normal mesendoderm specification, there isevidence that micromeres can induce mesendoderm in animal half blastomeresin the absence of detectable nuclear beta-catenin. It will be determinedif SUWnt8 can signal through the planar cell polarity pathway via theDisheveled protein to participate in mesendoderm specification in parallelwith the beta-catenin pathway. (4) The unique expression pattern of SUWnt8makes it a powerful reagent for studying the transcriptional basis ofmesendoderm specification. The trans-acting factors that mediate SUWnt8expression in the micromeres and the veg2 tier will be identified.Together, these studies will further our understanding of how the seaurchin A/V axis is specified and patterned and may provide insight intothe evolution of the A/V axis in bilaterians.