Figure 3.
How to establish an informative morphogen gradient. (a) Morphogens diffusing from a localized source (magenta) establish an exponentially decaying gradient over tissue space (l). A characteristic decay length (λ) can be defined as where the gradient amplitude (A) drops to its one by eth value. (b) Cell membrane is spatio-temporally organized as saturated lipids (green) phase separate into liquid-ordered nanodomains (i.e. rafts) in between unsaturated lipids (blue). Certain HSPGs, such as glypicans (yellow) associate with ordered nanodomains trapping morphogens and providing them to receptors (orange). Ligand-bound receptors undergo endocytosis. (c) Endocytic block results trapping of morphogens in extracellular space by receptors until reaching receptor saturation levels. This prohibits establishment of a gradient and diffusion of morphogens beyond a space. (d) Removal/absence of HSPGs results gradients to become shallow and unable to provide a positional information.