May’s Issue of CSH Protocols features a set of methods for Fluorescent In Situ Hybridization (FISH) from a group of scientists at Ludwig-Maximilians University Munich. While In Situ Hybridization dates back to 1969 (when several groups independently worked out methods), non-radioactive means of labeling probes didn’t come to the forefront until the 1980s.

We scientists who are of a certain age will remember how we used to have to schedule our week’s experiments around the day that the radioactive isotopes, usually 32P or 35S would arrive (”Are the hots in yet?”). Thankfully, colorimetric and fluorescent methods have since replaced the use of radioactive probes for most purposes. While many feel that the radioactive methods are still the gold standard for specificity and clarity of signal, the trade-offs (lower cost, lower health hazards, and not having to deal with paperwork and disposal of radioactive waste) have generally been worth it. Non-radioactive techniques also allow for whole-mount in situ methods, often more informative than trying to piece together data from histological sections.

One of this month’s featured protocols, Muller et al., describes methods for incorporating both fluorochromes and non-fluorescing haptens into DNA probes. The fluorescent probes are visualized directly, while the hapten-labeled probes are indirectly visualized using fluorescently labeled antibodies or proteins. You’ll also find protocols for FISH on histological sections and cultured mammalian cells.