FIGURE 10.7. Effects of geometry and degradation on levels of secreted molecules within epithelia.

FIGURE 10.7

Effects of geometry and degradation on levels of secreted molecules within epithelia. (A, B) Two processes remove polypeptides secreted into the intercellular space of an epithelium: diffusion into underlying connective tissue (stroma) and degradation within the epithelium. Given a molecule’s rate of production, its diffusivity, its rate of uptake and degradation, and the geometry of the epithelium, one may calculate its steady-state distribution. Here, such calculations are shown graphically, for epithelia of different thicknesses (in each picture the epithelium is oriented with the apical surface at the top). Epithelial thickness (“height”) is scaled according to the decay length of the molecule of interest. The shading in each picture depicts the concentration of the secreted molecule, with black representing the limiting concentration that would be achieved in an epithelium of infinite thickness. (A) The degradation capacity of the stroma is set at one-tenth that in the epithelium. In this case, intraepithelial concentrations of secreted molecules plateau while the epithelium is very thin. (B) The stroma is treated as a strong sink, i.e., few molecules that enter it escape undegraded. Now there is a large (and more physiological) range of epithelial thickness over which the concentrations of secreted molecules grow appreciably with tissue size. This is particularly true near the basal surface of the epithelium. (C) Follistatin (FST), a molecule that binds GDF11 and activin essentially irreversibly, is present at high levels in the basal lamina (arrow) and stroma (asterisk) at El 3 OE. Size bar: 100 urn. (D, E) INPs (visualized with Ngn1 in situ hybridization) become progressively localized to the basal surface of the OE over the course of development. (D)=E12.5; (E)=E18.5. nc=nasal cavity. Size bar: 100 pi. (Adapted from Lander, A.D. et al. PLoS Biol., 7, el5, 2009.)

From: Chapter 10, Feedback Regulation of Neurogenesis in the Mammalian Olfactory Epithelium: New Insights from Genetics and Systems Biology

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The Neurobiology of Olfaction.
Menini A, editor.
Boca Raton (FL): CRC Press/Taylor & Francis; 2010.
Copyright © 2010 by Taylor and Francis Group, LLC.

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