Figure 7

Model of apoC-II secretion. Dotted lines separate different developmental time points and, for each time point, the presented distal epithelial structures are co-observed in the same lung tissue sections. ApoC-II-containing secretory granules (dots) are observed in distal epithelia with no or small lumina from GD 16.5 to PN 0, but not in the distal epithelia with a large lumina between GD 18.5 and PN 0. These observations suggest that apoC-II secretion is delayed until apparition of the lumina. After its secretion, apoC-II can reach LPL molecules localized on the luminal surface of capillaries to activate LPL activity and fatty acid recruitment. According to this hypothesis, it could be difficult to detect apoC-II after its secretion because of the nature of its association with the tissue.