File:SHH signaling model.png

State-space diagram and network architecture for the Overshoot model

(A) The state-space diagram consistent with the Overshoot model is divided into four territories (I–IV) defined by the expression levels of ptc (or col) and dpp, consistent with the data in Figure 5. All cells in the anterior compartment are initially in Territory I (ptc OFF; dpp OFF), but only cells relatively far from the AP boundary, in which signaling levels are below the switching threshold, δ, remain in this territory (red trajectory). During the formation of the Hh gradient, cells located sufficiently close to the AP boundary visit transiently Territory II and express ptc, but not dpp. From the subset of cells that enter Territory II, those that remain exposed to the signal will continue expressing ptc and will eventually express dpp when crossing to Territory III (blue trajectory). However, cells in which Hh signaling ceases (for example, as a result of gradient refinement after the overshoot) will maintain dpp expression, but will stop expressing ptc. These cells will cross to Territory IV and remain there (gray trajectory). Note that Territory IV is not simply connected to Territory I (see boundary line demarcated by X's) as it is only accessible from Territory III. An additional territory (V) may be considered to include engrailed in the state-space model (see Figure S6G).

(B) The Overshoot model is inherent within the Hh network architecture.

The overshoot of Hh depends exclusively on Hh-dependent Ptc up-regulation (“Overshoot” module). However, distinct ptc/col and dpp can only be realized if dpp (but not ptc and col) expression is maintained in cells in which exposure of Hh is only transient. One way in which this can be effected at the molecular level is if a “Memory” module operates in the network. For example, dpp expression can be maintained specifically if a stable protease “X” that degrades the repressor form of Ci (Ci75) is up-regulated in response to Hh signaling; “Z” represents a Hh-independent activator that supports dpp expression (see Discussion).

Original File name: Journal.pbio.1000202.g007.png

Reference

Nahmad M & Stathopoulos A. (2009). Dynamic interpretation of hedgehog signaling in the Drosophila wing disc. PLoS Biol. , 7, e1000202. PMID: 19787036 DOI.

Copyright

© 2009 Nahmad, Stathopoulos. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Cite this page: Hill, M.A. (2024, April 27) Embryology SHH signaling model.png. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:SHH_signaling_model.png

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