Figure 2.

Morphogentic field formation and cytonemes.

(a) The Hh gradient is influenced by number of cytonemal contact points between cytonemes. (b) The Wnt gradient in the neural plate in zebrafish is regulated by the number of cytoneme contact sites. In addition, the expansion of the target tissue ensures long-range signalling. (c) The Fgf signalling gradient in air sac primordium cells in Drosophila is determined by the number of cytonemes and a positive-feedback loop regulation as Fgf signalling enhances cytoneme formation. The red graphs illustrate the intial gradient, whereas the yellow curves illustrate the gradient after the indicated alterations in cytoneme emergence.