Formaldehyde fixation of Drosophila tissues onto slides for whole-mount FISH

This protocol describes the formaldehyde fixation of Drosophila tissues other than egg chambers. It provides a general approach to fixing tissue or cells onto microscope slides in a manner compatible with whole-mount fluorescent in situ hybridization (FISH) analysis. The procedure includes a simple formaldehyde fixation in buffer, followed by postfixation in cold ethanol. Postfixation of the tissue in methanol or ethanol can markedly improve permeability. In some instances, it may be preferable to fix tissue onto coverslips, because microscope optics are usually designed to optimize imaging immediately adjacent to the coverslip. On the other hand, coverslips are much more fragile and harder to manipulate.