Fig. 3. Organization of the endosomal recycling system in polarized epithelial cells. The SAC/CE is accessible both to apical and basolateral early-endosome-derived transport pathways. Its most distal part is defined as the ARE and is considered an integral subcompartment whose stability is dependent on microtubules. This subcompartment is involved in relaying molecules to the apical surface as the final step in the overall basolateral-to-apical transcytotic pathway. For further details, see text. Colored arrows depict apical or basolateral transport routes. AEE, apical early endosome; AJ, adherens junctions; ARE, apical recycling endosome; BEE, basolateral early endosome; CE, common endosome; dIgA, dimeric immunoglobulin A/pIg-receptor complex; GlcCer, glucosylceramide; SAC, subapical compartment; SM, sphingomyelin; TfR, transferrin receptor; TJ, tight junctions.