Improved preservation of ultrastructure in difficult-to-fix organisms by high pressure freezing and freeze substitution: I. Drosophila melanogaster and Strongylocentrotus purpuratus embryos.

In this study, we have applied the techniques of high pressure freezing and freeze substitution to embryonic cell types which are usually difficult to fix properly for electron microscopy. In both Drosophila and Strongylocentrotus purpuratus, we see improved preservation of both membrane systems and cytoskeleton when compared to published results on the same cells using conventional electron microscope (EM) fixation methods. Finally, we have seen that postembedding labelling of sections is possible even after light osmium fixation during freeze substitution.