Fig. 2. Local activation of phenoloxidase in the Drosophila clot. Drosophila hemolymph clots were prepared as described (Bidla et al., 2005) and examined with phase-contrast (A,C,E) and bright field microscopy (B,D,F). Melanization is mostly restricted to cell fragments (asterisks) and folds in the clot matrix (arrowheads indicate clot folds, the arrows indicate plasmatocytes). Bars, 10 µm. (E,F) Plasmatocytes inside the clot (filled arrows) show melanization beginning on their surface. Plasmatocytes outside the clot (open arrow) are not melanized. (G,H) Overexpression of Spn27A (da-GAL4 driven) leads to complete loss of melanization, although clot fibers are formed (visible in phase-contrast, also visible in bright field images G,H). The insets in B and H show PO activity analyzed with a dot-blot assay (see Materials and Methods).