The GSL biosynthetic pathway is active in both germ line and follicle cells. The GSL biosynthetic pathway is active in both germ line and follicle cells. (A) Upon loss of brn function, the intermediate product mactosylceramide (MacCer), synthesized by Egh, cannot be extended and accumulates. This product is specifically recognized by our antibody. (B) Confocal images of brn homozygous mutant Drosophila egg chambers of the indicated stages stained with anti-MacCer antibody (blue). The asterisk marks an egg chamber that could not be staged because it is compound. MacCer staining (shown alone in the bottom row of panels) is detected in the germarium (germ) and in newly budded egg chambers. Expression disappears between stages 4 and 7. From stage 8 onward, MacCer staining is present at the membrane of follicle cells. It is also observed in nurse cells at their membranes (arrows), but mostly in intracellular aggregates. In oocytes, MacCer staining is uniform at stage 8 and shifts towards the anterior cortex between stages 9 and 10 to remain strong in the vicinity of the nucleus. Wild-type egg chambers are negative for MacCer staining (not shown). Anterior is to the left and dorsal is up. Sandrine Pizette et al. Development 2009;136:551-561 © 2009.