Wednesday, February 2, 2000

K. Itoh and S. Sokol, 1999. Axis determination by inhibition of Wnt signaling in Xenopus. Genes Dev 13:2328-2336.

General discussion questions:

1. What was the major question addressed?
2. What did the author(s) conclude?
3. What experimental evidence and arguments did the author(s) use to justify this conclusion?
4. What experimental techniques were used to generate this evidence?
5. What are your criticisms of this paper? (positive and/or negative)
6. What did you not understand about this paper?

Specific discussion questions:

1. Personally, I'm comfused about what type of molecule is being used in the experiment. For example, the article refers to the form of Xwnt8 used as mRNA, other times as a ligand. Does  Xwnt8 mRNA had different effects on the embryo than adding the Xwnt8 ligand?  ISn't the mRNA just tranlated into protein form anyway?

2. In the paper Itoh and Sokol mention that the effect of ECD8 mRNA was dose dependent.  Could these different doses of ECD8 mRNA, which in turn changed the effect on axes, be considered a threshold/gradient model of signaling?

3. Why do WNT ligands act to suppress dorsalization in ventral blastomeres but do not have this effect in dorsal blastomeres, only aiding in elongation in dorsal sections of the embryo?

4. I had trouble following the part about ECD8 and Xwnt8 activating markers by different mechansims, so what are the differences between the mechanisms used?

5. At one point in the article, the authors write that "exogenous Xwnt8 and ECD8 stimulate dorsal developement via different molecular pathways." Is this sentence implying that Xwnt8 stimulates dorsal development (I understood it did the complete opposite) or that both proteins have an effect on dorsalization - although their effects are different.

6. What effect does ECD8 have on Wnt in mammal embryos?  Also does ECD8 have further effects after the axises have been established?

7.What role does the Wnt signalling pathway play in the anteroposterior axis formation and through what mechanisms does the ECD8 moderate the Wnt

8.What inhibits the activation of organizer markers and muscle specific actin in animal pole cells compared to ventral marginal zone cells when both are
treated with equal doses of ECD8, know to stimulate dorsoanterior ectoderm development?