Gastrulation and Neural Induction
Jen-Yi Lee, Richard M. Harland, 2007. Actomyosin contractility and microtubules drive apical constriction in Xenopus bottle cells. Developmental Biology 311 40–52.
John B. Wallingford, Kevin M. Vogeli And Richard M. Harland, 2001. Regulation of convergent extension in Xenopus by Wnt5a and Frizzled-8 is independent of the canonical Wnt pathway. Int. J. Dev. Biol. 45: 225-227
John B. Wallingford*, et.al. & Richard M. Harland, 2000. Dishevelled controls cell polarity during Xenopus gastrulation. NATURE VOL 405.
Briefly tell us a bit about yourself, your career path over the years, and specifically what led you to begin working on gastrulation in Xenopus.
How does F-actin end up in the right area of the pre-bottle cells in order to help cause bottle cell formation?
In the discussion of the “Actomyosin in Xenopus” paper, you state that the role of adhesion and the microtubules involved in cell to cell adhesion, is largely unknown with regard to bottle cells. You also state that microtubules “affect contractility through adhesion”. What do you mean by this? What do you think is the role of cell-cell adhesion in the bottle cell formation is?
In the paper on 2007 it was said that intact but not dynamic microtubules are required in bottle cell apical construction, and that the function of microtubules was independent from actin or myosin. Based on these data can you elaborate on exactly what role you feel microtubules play in the process of bottle cell apical construction?
Both an overexpression of Xdd1 and an overexpression of Xdsh inhibited convergent extension, likewise inhibition of Xdsh disrupted convergent extension. If both inhibition and overexpression of Xdsh disrupts convergent extension, then what is the mechanism that controls/balances expression of Xdsh?
What regulates the expression of Xwnt5a and Nxfz-8 in the dorsal mesoderm of Xenopus? Is it a negative feedback pathway that occurs relative to the level of integrin-extracellular fibronectin binding during convergent extension? Or do they exist in pre-established gradients?
In the letters to nature paper entitled “Dishevelled controls cell polarity during Xenopus gastrulation”, you write in the paper that overexpression of DN-GSK3 alone in the DMZ did not significantly affect convergent extension, but in the figure directly below which is an analysis of convergent extension including a comparison of control with DN-GSK3 cells, you write that “all differences shown are statistically significant (P< 0.01),” how do you reconcile these two claims with your overall findings?
The end of the article titled “Regulation of convergent extension in Xenopus by Wnt5a and Frizzled-8 is independent of the canonical Wnt pathway” mentions the possibility of calcium playing a role in controlling convergent extension. Has your lab researched this any further? What do you think initially triggers the calcium wave? Is it started by just one cell or a group of coordinated cells? Specifically how is Wnt5a leading to Calcium release?
Since Frizzled activates a PKC pathway (as shown in Figure 1 of the 2001 paper), leading to calcium release in the cell, is it possible that this pathway is responsible for activating the apical cell’s actomyosin cytoskeleton during bottle cell constriction?
How applicable are these models of convergent extension to mammals? Is there a DSH-like pathway operating in the gastrulation of Homo sapiens (mammals), and if so how does it compare and contrast to its role in Drosophila and Xenopus? And in line with this question, why do you think two Wnt pathways have evolved (canonical versus noncanonical)?
Currently in your opinion what are the most pressing questions in the field of gastrulation, and what steps is your lab taking to address those questions?