Specification and Patterning of the Animal-Vegetal Axis

University Of Hawaii, Honolulu

Investigators

Abstract

0110532 Wikramanayake Depletion of nuclear beta-catenin in early sea urchin embryos affects the fates of multiple cell lineages along the animal-vegetal (A/V) axis. It is known that the micromeres, which form the early signaling center that specifies mesendoderm, require nuclear beta-catenin to become competent to carry out their inductive functions. Beta-catenin signaling is also required in the veg2 lineage for these cells to respond to micromere signals and to become specified as mesendoderm. Identifying transcriptional targets of beta-catenin and elucidating their functions would be a critical step in defining the molecular basis of mesendoderm specification. This proposal will focus on SUWnt8, a nuclear beta-catenin-sensitive Wnt gene that is activated in the micromeres coincident with the entry of beta-catenin into the nuclei of these cells and in the veg2 tier shortly after transit of beta-catenin into the nuclei of this cell tier. Four proposed specific aims will define the function of SUWnt8 in these cell lineages and will further the understanding of mesendoderm specification in the sea urchin embryo. These aims are: (1) To determine the role of cell interactions in regulating early SUWnt8 expression in the mesendoderm domain. This will provide insight into the relative roles of cell autonomous and non cell-autonomous mechanisms in early mesendoderm specification. (2) To determine how SUWnt8 participates in early mesendoderm specification by elucidating its role in the micromeres and the veg2 tier by blocking its activity using morpholino antisense oligonucleotide-mediated translational inhibition. Additionally, a possible role for SUWnt8 in maintaining nuclear beta-catenin levels in vegetal cells and in suppressing the activity of animalizing transcription factors in vegetal cells will be determined. (3) While nuclear beta-catenin is required for normal mesendoderm specification, there is evidence that micromeres can induce mesendoderm in animal half blastomeres in the absence of detectable nuclear beta-catenin. It will be determined if SUWnt8 can signal through the planar cell polarity pathway via the Disheveled protein to participate in mesendoderm specification in parallel with the beta-catenin pathway. (4) The unique expression pattern of SUWnt8 makes it a powerful reagent for studying the transcriptional basis of mesendoderm specification. The trans-acting factors that mediate SUWnt8 expression in the micromeres and the veg2 tier will be identified. Together, these studies will further our understanding of how the sea urchin A/V axis is specified and patterned and may provide insight into the evolution of the A/V axis in bilaterians.