|
|
|
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
|
Fig. 1. Finite element model (FEM) of the vertebrate developing neural tube.
(A) One-dimensional projection of neural tube tissue. A transverse
cross section of a stage 16 chick embryo depicts expression of shh
(green) and pax6 (red) [adapted, with permission, from Ericson et al.
(Ericson et al., 1997b)].
White labels indicate subsequent mature stage 26 cell fates. MN, motoneurons;
V1-3, distinct populations of ventral interneurons. On the right, cells A-C
are depicted with a surface membrane (orange), nuclei (dashed ovals), and
extracellular space (light gray). In the FEM mesh, each black circle
represents a mesh boundary, and each gray `x' represents a node where
concentrations are defined in the mesh. (B) The Shh core signaling
network (red dashed line with internalization labeled as I) and hypothesized
accessory mechanisms (labeled II-VI) are shown around a representative cell.
Arrows between proteins represent binding or dissociation, arrows from genes
to proteins represent expression, and arrows from proteins to genes indicate
activation or repression. Vit, vitronectin; Smo, Smoothened. At the cellular
level, Shh induces cell fate switching by interacting with its transmembrane
receptor, Patched (Ptc). In absence of Shh, Ptc represses the signaling
activity of the transmembrane protein Smo and therefore acts as a repressor of
Shh signaling as described previously (Lai
et al., 2004). gli upregulation represents positive
feedback, whereas ptc upregulation yields negative feedback.
|
