We've recently encountered a problem trying to fix embryos produced by females that over-express oskar (mat-alpha-tubulin-GAL4 driven expression of UAS-osk). We routinely process embryos for a variety of applications by bleach dechorionation (50% bleach:water) followed by fixation in heptane:formaldehyde mix (pretty standard protocol). However, following dechorionation, the embryos from UAS-osk mat-alpha-tubulin-GAL4 females are very sticky and aggregate, refusing to dissociate in either heptane or the aqueous fix phase. As a result the embryos don't fix or stain properly. We've tried rinsing the embryos in PBT (0.1% triton) after dechorionation, but that has minimal effect on embryo aggregation. Has anyone else seen this (with any genotype)? Better yet, does anyone have a suggestion/solution?