The PI is interested in the maternal mechanisms that regulate the specification of the animal-vegetal (A/V) axis in the sea urchin embryo, and in elucidating how this maternal information is used in germ layer segregation. One of the first molecular asymmetries seen along the A/V axis is the entry of B-catenin into vegetal cell nuclei. Nuclear B-catenin, which is the transducer of the canonical Wnt signal, is essential for specification of endomesoderm, and also for pattern formation along the A/V axis. Elucidating how canonical Wnt signaling is activated in vegetal cells will provide insight into the mechanisms that specify this axis. Work done during the previous granting period has shown that the Dishevelled (Dsh) protein becomes localized to vegetal vesicular cortical structures following fertilization. Dsh interaction with these membrane vesicles then regulates the nuclear entry of B-catenin and activation of canonical Wnt signaling. An early nuclear target of B-catenin in vegetal cells is the signaling molecule SpWnt8. Results from the previous granting period have shown that SpWnt8 is required for primary mesenchyme differentiation and the continued specification of the endomesoderm. These data suggests that SpWnt8 has an early function to maintain nuclear B-catenin levels in vegetal cells, and a late function at the late blastula stage to regulate endomesoderm gene expression and gastrulation. The late function of SpWnt8 appears to require a non-canonical Wnt signaling pathway that also involves Dsh.
To further understand Dsh and SpWnt8 regulation and function in the sea urchin embryo, three specific aims will be pursued: 1) To identify molecular mechanisms that regulate Dsh activity in early embryos. These studies will reveal the mechanisms that selectively activate canonical Wnt signaling in vegetal cells of the sea urchin embryo, and have the potential to reveal the molecular basis for the animal-vegetal axis; 2) To functionally analyze the role of key planar cell polarity pathway (PCP) genes animal-vegetal axis patterning. These studies will reveal if signaling through this non-canonical Wnt pathway regulates endomesoderm formation and gastrulation in the early embryo; 3) To determine the intracellular pathways activated by SpWnt8 to regulate endomesodermal cell fates. These studies will reveal if SpWnt8 can signal via the canonical and non-canonical Wnt pathways, and further, will reveal the specific PCP pathway activated by SpWnt8.
Together, these studies will increase 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. These studies will also include postdocs, graduate students and undergraduate students from groups underrepresented in science. Results from the work will also be communicated to students enrolled in the PI's Developmental Biology classes.
