Morphogenesis of the nerve cord

Nodal is a secreted protein that affects the behavior of other cells through specific binding to the cell surface receptors.
Overexpression or inhibition of Nodal resulted in impaired morphogenesis of the dorsal neural tube.
These results indicate that Nodal is required for morphogenesis of the neural tube.
Nodal の機能阻害
(n) Normal embryo.  (o) Inhibition of  the Nodal signaling causes defects in neural tube formation.
Nodal は cdx の転写を活性化する
Nodal activates the expression of the cdx gene.
(Left) Expression of the cdx mRNA in normal embryo.  
(Center) Overexpression of Nodal ectopically activated cdx (red arrowheads).
(Right) Inhibition of the Nodal signaling suppressed cdx (blue arrowheads).

Inhibition of the cdx function, by using a dominant-negative form of cdx, resulted in abnormal morphogenesis of the neural tube.

In the figure on the right side, the top panel shows a normal tailbud embryo, viewed from the dorsal side.  Neural tube was stained in purple.  The bottom panel shows the embryo where the function of cdx was disturbed.  Neural tube cells were not converged to the dorsal midline.

This result suggest that cdx is required for mediating the Nodal signling during neural tube morphogenesis.  
cdx の機能阻害

Like cdx, Nodal activates many other genes, as revealed by a microarray analysis.
The Nodal target genes include those encoding the extracellular matrix proteins, cell adhesion
molecules.  These proteins may be directly involved in morphogenetic movement of neural tube cells.
We are now trying to examine whether these genes really contribute to neural tube formation.

*Mita, K., Koyanagi, R., Azumi, K., Sabau, S.V. & Fujiwara, S. (2010) Identification of genes downstream of Nodal in the Ciona intestinalis embryo. Zoological Science 27, 69-75.
*Mita, K. & Fujiwara, S. (2007) Nodal regulates neural tube formation in the Ciona intestinalis embryo.  Dev. Genes Evol. 217: 593-601.