Figure 1.

Structure and biogenesis of SJs. (A) Diagram of a polarized epithelium, showing the location of the adherens junction (AJ) and the septate junction (SJ). Apical is to the top. Note that the septa do not completely encircle the cell but are discontinuous, generating an extended path from the apical to basal side of the epithelium. (B) Electron micrograph of the epidermis in a stage 17 wild type embryo showing the electron dense extracellular septa in the SJ. (C,D) Diagram of the anterior portion (including a salivary gland) of a stage 14 (C) and a stage 17 (D) wild type embryo that had been injected with a 10-kDa rhodamine-labeled dextran (pink). The labeled dextran can cross the salivary gland epithelium and enter the lumen in a stage 14 embryo, but not in a stage 17 embryo due to the formation of the SJ. (E–G) Confocal micrographs of hindguts from w¹¹¹⁸ stage 13–16 embryos stained with antibodies against the AJ protein E-cadherin (in magenta) and the SJ protein Mcr in cyan. (E’–G’) Inverted images of the Mcr channel from (E–G). Mcr localizes all along the lateral membrane in stage 13 embryos (arrows) and begins to be enriched at the SJ (asterisk) with some lateral expression (arrow) and punctate cytoplasmic expression in stage 14 (arrow in inset). By stage 16, Mcr is tightly localized to the region of the SJ (asterisks) and is clearly basal to the AJ protein E cadherin.