Fig. 9. -adaptin is associated with IgA-containing endosomes. (A) In a medial plane of polarized cells, immunolocalized -adaptin associates with multiple intracellular compartments. Punctate compartments correspond to endosomes (see below) while larger tubular structures are likely to be elements of the trans-Golgi network. Treatment of cells with BFA both dissociates -adaptin from intracellular compartments, and also tubulates endosomes, as shown in the medial plane of a field of cells pretreated with BFA for 15 minutes, then incubated with Alexa488-Tf for 40 minutes in the continued presence of BFA (B,C). A medial plane of control cells incubated with Alexa488-Tf shows a limited colocalization of Tf with -adaptin (D-F). In contrast, cells incubated with Alexa488-IgA show a close correspondence between the distributions of IgA and -adaptin. This colocalization is particularly apparent in apical planes, where the patterns of the two closely match in AREs and punctate endosomes (G-I), but also in the focal plane of the same cells collected 6 microns lower (J-L), where the two colocalize in medial endosomes. A few examples of IgA-containing endosomes associated with -adaptin are noted with arrows. Scale bar, 10 µm.