Figure 1. Apical extracellular matrices of Caenorhabditis elegans, Drosophila melanogaster, and the vertebrate inner ear.

a. Cartoon of adult C. elegans cuticle, longitudinal section. The cuticle consists of an outer surface coat (gold), a lipid-rich epicuticle (red), collagenous cuticle proper (divided into cortical [blue], medial [gray], fibrous [purple], and basal [navy] layers). The cuticle is secreted by the underlying cellular epidermis (green), internal to which is a basement membrane (burgundy). b. Cartoon of D. melanogaster cuticle, consisting of an outer lipid-rich envelope (red), glycoprotein-rich epicuticle (yellow), and the chitinous procuticle (blue), formed in the assembly zone at the apical surface of the underlying epidermis (green). Pore canals form channels through the cuticle layers to the surface. c. Cartoon of D. melanogaster mature tracheal cuticle, showing taenidial folds (blue). Envelope and epicuticle are not shown for simplicity. d. The vertebrate tectorial membrane (blue) is shown in cross section, attached to the underlying epithelial ridge of the organ of Corti at its medial edge and to the stereocilia of the outer hair cells at its lateral edge. The underlying basement membrane is known as the basilar membrane.